Reduction of Non-Revenue water as a water demand management strategy(Case Study)

Reduction of Non-Revenue Water as a Water Demand Management Tool

Dube Nkosiphile N009 5117L

FINAL YEAR PROJECT:

REDUCTION OF NON REVENUE WATER AS A WATER

DEMAND MANAGEMENT TOOL: A case study of Cowdray

Park in Bulawayo.

FACULTY OF INDUSTRIAL TECHNOLOGY

CIVIL AND WATER ENGINEERING DEPARTMENT

STUDENT : DUBE NKOSIPHILE

STUDENT NUMBER : N0095117L

SUPERVISOR : Dr. M.MAGOMBEYI

MAY 2014


Dube Nkosiphile N009 5117L

FINAL YEAR PROJECT

BY

DUBE NKOSIPHILE

(N009 5117L)

“A PROJECT SUBMITTED TO THE FACULTY OF INDUSTRIAL TECHNOLOGY,

NATIONAL UNIVERSITY OF SCIENCE AND TECHNOLOGY, IN PARTIAL

FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF

ENGINEERING HONOURS IN THE FIELD OF CIVIL AND WATER ENGINEERING”

DEPARTMEBT OF CIVIL AND WATER ENGINEERING

FACULTY OF INDUSTRIAL TECHNOLOGY

NATIONAL UNIVERSITY OF SCIENCE AND TECHNOLOGY

MAY 2014


i

DECLARATION

I ………………………………………………. Hereby declare to the Registrar of

Examinations at the National University of Science and Technology, that the work

contained in this project is the result of my own original work. With the exception of

such quotations or references that have been attributed to their authors or sources

and that all photographs, sketches, maps, plans, graphs and pictograms were made

by me except where it is acknowledged that someone is the author. To the best of my

knowledge, it has never been submitted before, for any degree or examination in any

University or Institution.

Dated this ……………… day of …………………….in the year ……………………..

Signed by:

Author: ……………………………………..

Dube Nkosiphile


ii

DEDICATIONS

To the Lord God Almighty,

Lorraine, Sthandazile, Sandile and Zoey


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ACKNOWLEDGEMENTS

BLESS THE LORD OH MY SOUL AND ALL THAT IS WITHIN ME …… NEVER

FORGET HIS BENEFITS…… (PSA 103 VS 1-5)

I would like to express my most profound gratitude to all the people who made a

contribution to my final year project. Special thanks goes to my Project supervisor

Dr. M.Magombeyi for the support, inspiration, encouragement, motivation, dedication,

comments and greatly helpful corrections. Sincere appreciation also goes to Mrs.K.G

Sibanda, Mr F.M.Nkawu, Sandile S Sibanda, the Directors, Engineers, Technicians

and the Administration staff at City Of Bulawayo who were so kind and warm to work

with as even when they were working under pressure, managed to spare time for me

whenever l made consultations with them. Their assistance is acknowledged with

grateful thanks, without them the academic journey would not have been complete.


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ANNOTATIONS

AC Asbestos Cement

AWWA American Water Works Association

CARL Current Annual Real Losses

CoB City of Bulawayo

DMA District Metered Area

ILI Infrastructural Leakage Index

IWA International Water Authority

MNF Minimum Night Flow

MoC Method of Characteristic

NRW Non-Revenue Water

PI Performance Indicator

PRV Pressure Reducing Valve

PVC Polyvinyl Chloride

UARL Unavoidable Annual Real Losses


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ABSTRACT

Chronic water losses has been the evil that the Bulawayo City Council had to face in

terms of water management over the decades, this may not have mattered much

during an era of assumed plenty. But the rapid growth of Bulawayo’s towns and cities

in particular the development of the high density area of Cowdray Park, has meant

that there is much less water in the urban centres. The loss of an estimated 1.2 million

cubic meters of treated water every year is no longer something that the water utility

can ignore. Reducing these water losses is critical to efficient resource utilization,

efficient utility management and enhanced consumer satisfaction. Wherever active

water loss reduction programs have been initiated and sustained, the gains to

consumers and utilities alike have been significant. Frauendorfer and Liemberger point

out that the costs of improved service delivery are much lower when undertaken

through investments in non-revenue water reduction rather than through investments

in capital projects to augment supply capacities.

The results show that the Non-Revenue Water (NRW) level (for Cowdray Park) is

currently estimated at 50% of the water produced as reported in the Water Balance in

International Water Association(IWA, 1996)Standard Format or 3 861.77m3/day of the

7 704.5m3/day produced by the City of Bulawayo(CoB) . Strategies employed reduced

the Current Annual Real Loss (CARL) from 2 332.8m3/day to 1 555.2m3/day

(Recovering an estimated 777.6m3/day), while the Apparent and Billing Loss (water

that is used but not billed) was reduced from approximately 1528.97m3/day to an

estimated 1443.88m3/day (Recovering an estimated 85.09m3/day).

It was then concluded that these high levels of Non-Revenue Water are a cause for

concern and should be reduced as a matter of urgency so as to effectively manage

water demand. The potential exists to further reduce the Non-Revenue water from the

40% obtained after implementing strategies to a further 10 – 15%. This can be

achieved by adoption of the recommended strategies inclusive of;

Active leak detection methods

Cutting off illegal consumers

Pressure management

Effective asset management


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Table of Contents

DECLARATION……………………………………………………………………………...i

DEDICATION…………………………………………………………………………….…..ii

ACKNOWLEDGEMENTS……………………………………………………………….....iii

ANNOTATIONS……………………………………………………………………………..iv

ABSTRACT…………………………………………………………………………………..v

TABLE OF CONTENTS…………………………………………………………………….vi

LIST OF FIGURES……………………………………………………………………….ix

LIST OF TABLES…………………………………………………………………………….x

1. INTRODUCTION……………………………………………………………………1

1.1. Problem statement: Challenge encountered by the City of Bulawayo ........... 1

1.2. Proposed solution for criterion reservoir zone ............................................... 3

1.3. Overall Objective ........................................................................................... 4

1.3.1. Specific objectives .................................................................................. 4

1.3.2. Methodology ........................................................................................... 4

1.4. Expected results ............................................................................................ 6

2. LITERATURE REVIEW ....................................................................................... 8

2.1. Water Conservation and Demand Management ........................................... 8

2.1.1. Water conservation ................................................................................. 8

2.1.2. Demand management ............................................................................ 9

2.2. The integrated Water Resource Management (IWRM). .............................. 11

2.2.1. Components and Definitions of Non-Revenue Water (NRW) ............... 11

2.3. Burst and Background Leaks. ..................................................................... 13

2.4. Water Balance ............................................................................................. 14

2.5. Introduction to BURST AND BACKGROUND ESTIMATE (BABE) CONCEPT

15

2.6. Impacts of NRW: The Vicious and Virtuous circles. .................................... 20

2.7. Strategy for Dealing with Water Losses ...................................................... 21

2.7.1. Calculation of bursts ............................................................................. 27


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2.7.2. Pressure correction .............................................................................. 27

3. Study Area ......................................................................................................... 31

3.1. Introduction ................................................................................................. 31

3.2. Water distribution system in Cowdray Park ................................................. 32

3.2.1. Service pipelines .................................................................................. 32

3.2.2. Present water supply situation .............................................................. 33

3.2.3. Existing water supply Water system and Water sources ...................... 34

3.2.4. Short term extensions of the water sources.......................................... 34

3.3. Water Treatment ......................................................................................... 35

3.4. Water delivery facilities ............................................................................... 35

3.5. Reservoirs ................................................................................................... 36

3.6. Pressure Zones ........................................................................................... 37

3.7. Water Meters ............................................................................................... 38

4. METHODOLOGY .............................................................................................. 39

4.1. STUDY DESIGN ......................................................................................... 39

4.1.1. Project Activities ................................................................................... 39

4.1.2. Sources of Data .................................................................................... 39

4.2. Sampling plan ............................................................................................. 40

4.3. Flow measurements .................................................................................... 42

4.4. Pipeline Survey ........................................................................................... 43

4.5. House inspection ......................................................................................... 43

4.6. System inventory ......................................................................................... 44

4.7. Non-Revenue Water calculation .................................................................. 44

4.7.1. Softwares .............................................................................................. 46

4.8. Water Balance ............................................................................................. 51

4.9. Calculation of Real Losses .......................................................................... 54

4.9.1. Leak Simulation .................................................................................... 54

4.9.2. Calculating Real Loss Performance Indicators ..................................... 56

4.10. Data analysis and Strategy implementation ............................................. 59

4.11. Summary of methodology: ....................................................................... 63

5. RESULTS AND DISCUSSION .......................................................................... 65

5.1. Introduction ................................................................................................. 65

5.2. Data logging ................................................................................................ 65


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5.3. System input volume (SIV) .......................................................................... 67

5.4. Apparent losses .......................................................................................... 68

5.5. Real losses.................................................................................................. 68

5.6. Water Balance ............................................................................................. 71

5.7. Strategies Implemented .............................................................................. 72

5.8. Infrastructural leakage index (ILI) ................................................................ 72

6. CONCLUSIONS AND RECOMMENDATIONS .................................................. 75

6.1. Introduction ................................................................................................. 75

6.2. Non-revenue water ...................................................................................... 76

6.3. Projections of losses ................................................................................... 76

6.4. Findings ...................................................................................................... 76

6.5. RECOMMENDATIONS ............................................................................... 77

6.5.1. Asset Management ............................................................................... 77

6.5.2. Pressure Management ......................................................................... 79

6.5.3. Active Leak Detection ........................................................................... 80

6.5.4. Efficiency in effecting Repairs ............................................................... 80

6.5.5. Capacity building .................................................................................. 81

6.5.6. Significance of the study ....................................................................... 81

REFERENCES………………………………………………………………81

APPENDICES……………………………………………………………….84


ix

LIST OF FIGURES

Figure 1.1 Water Balance for Bulawayo in International Water Association (IWA)

Standard format ........................................................................................................ 3

Figure 2.1 Paradigm shift for Water demand management ........................................ 8

Figure 2.2. Component of Non-Revenue Water ....................................................... 13

Figure 2.3. Traditional Water Balance ...................................................................... 17

Figure 2.4. BABE Water Balance Approach ............................................................. 18

Figure 2.5 Recommended BABE Water Balance Components ............................... 19

Figure 2.6 The Vicious NRW cycle ........................................................................... 20

Figure 2.7 The Virtuous NRW cycle ......................................................................... 21

Figure 2.8 Breakdown of night flow .......................................................................... 24

Figure 3.1 Summary Description of Cowdray Park Area .......................................... 31

Figure 3.2: Water Disribution in Cowdray Park ........................................................ 33

Figure 4.1 Flow and pressure measurements in a PRV using a DataLogger ........... 42

Figure 4.2 Flow and pressure measurements in households ................................... 44

Figure 4.3 Example of sensitivity analysis ................................................................ 49

Figure 4.4 Leak simulation by the Method of Characteristics (MOC) ....................... 55

Figure 4.5 Leak opening coefficient versus the square-root of the head loss across the

leak for the five leak cases ....................................................................................... 56

Figure 4.6 (c) and (d) variation of real loss with type of maintenance strategy ......... 60

Figure 4.7 Real loss reduction strategies ................................................................. 61

Figure 4.8 Methodology Flow Chart ......................................................................... 64

Figure 5.1 Consumption and pressure versus time graph measured at the District

meter ........................................................................................................................ 66

Figure 5.2 Pressure patterns at households ............................................................. 67

Figure 6.1 Pressure/ leakage relationship ............................................................... 79

Figure 6.2 The effect of time on the total volume lost .............................................. 80

file:///H:/nkosi%20proj/Final_Year_Project_Draft%5b1%5d.docx%23_Toc332369333


x

LIST OF TABLES

Table 1.1 Activities and Timeline ................................................................................ 7

Table 2.1 Standard Water Balance format .............................................................. 15

Table 4.1 Sample sizes ........................................................................................... 42

Table 4.2 The Water Balance standard format ......................................................... 53

Table 4.3 Flow rates for bursts ................................................................................. 57

Table 4.4 Flow rates for background losses ............................................................. 57

Table 4.5 ILI interpretation banding system ............................................................ 58

Table 5.1 Test house meters .................................................................................... 69

Table 5.2 Cowdray Park water balance in standard IWA format ............................. 71

Table 5.3. The ILI interpretation banding system ..................................................... 73

Table 5.4 Difference before and after implementation of strategies. ........................ 73

1

1. INTRODUCTION

With the gap closing between water demand and supply for urban areas, which comes

with the increasing human population and associated demand for resources which

require water, especially food we must not limit the solution to supply options only (that

is, to develop the next source of water), but also consider demand-side options, such

as minimising water losses, and influencing demand to more desirable levels through

structural ( for instance, retrofitting of water appliances, recycling and re-use, active or

reactive leak detection and repair), socio-cultural (for example. education and

awareness campaigns, creative and innovative presentation of utility bills), legal (e.g.

restrictions on use) and economic (for example water tariff structure policy that is

pricing) measures. (Asian Development Bank, 2010)

A readily available and applicable solution is the Reduction of Non-Revenue water. -

Revenue Water (NRW) being defined as water that is produced, but “lost” before final

consumption, and hence not billed to the end user of the service. NRW is calculated

using the Top Down approach using the Benchleak method. (www.iwapublishing.com,

undated)

It is in this light that a case study is to be undertaken by the student focusing on

Cowdray Park network; with the area being chosen on the basis of it being a

developing area hence the City of Bulawayo (CoB) has not much data on that area in

terms of Input Volume and billing database. Cowdray Park is prone to illegal

connections, frequent leaks and bursts hence it would be an ideal area to study.(City

of Bulawayo, 2012)

1.1. Problem statement: Challenge encountered by the City of Bulawayo

According to the City of Bulawayo (CoB) Master Plan Non-Revenue Water (NRW)

levels at a macro scale (Citywide) is currently estimated at 69% of the water produced

,as reported in the Water Balance in International Water Association(IWA,

http://www.iwapublishing.com/


2

1996)Standard Format below or 110Mℓ/day of the 156,43Mℓ/day produced by the CoB

(Bosch Stemele,2012). Of this, the potential exists to reduce the Current Annual Real

Loss (CARL) from approximately 59,7Mℓ/day to approximately 20,5Mℓ/day

(Recovering an estimated 39,21Mℓ/day), while the Apparent and Billing Loss (water

that is used but not billed due to under-reading meters, incorrect meter readings etc.)

may be reduced from approximately 50,32M/day to an estimated 22,47Mℓ/day

(Recovering an estimated 27,85Mℓ/day) (target as per City of Bulawayo water and

wastewater master plan). These high levels of Non-Revenue Water are a cause for

concern and should be addressed as a matter of urgency so as to effectively manage

water demand. The City already is water stressed due to prolonged droughts and low

and unreliable rainfall while water scarcity is not too distant in future as evident by

water shedding as a consequence of other dams being decommissioned (City of

Bulawayo, 2012).


3

System Input

Volume

156 425 Kℓ/day

Authorised

Consumption

69 129 Kℓ/day

Billed Authorised

Consumption

46 393 Kℓ/day

Billed Metered

Consumption

46 393 Kℓ/day

Revenue Water

46 393 Kℓ/day

Billed Unmetered

Consumption

0 Kℓ/day

Unbilled

Authorised

Consumption

22 736 Kℓ/day

Unbilled Metered

Consumption

22 636 Kℓ/day

Non-Revenue

Water(NRW)

110 032 Kℓ/day

Unbilled Unmetered

Consumption

100Kℓ/day

Water Losses

87 296 Kℓ/day

Apparent Losses

27 581 Kℓ/day

Unauthorised

Consumption

22 942 Kℓ/day

Customer Metering

Inaccuracies

4 639 Kℓ/day

Real Losses

59 715 Kℓ/day

Leakage on

Transmission and/or

Distribution Mains

16 434 Kℓ/day

Leakage and

overflows on storage

facilities

500 Kℓ/day Leakage on service

connections

42 872 Kℓ/day

Figure 2.1 Water Balance for Bulawayo in International Water Association (IWA)

Standard format (Bosche stemele, 2012)

1.2. Proposed solution for criterion reservoir zone

The fact that water is finite and its scarcity is on the increase means that the City needs

to develop effective mechanisms of managing it. The conventional approaches to

water management have been to construct elaborate dams to increase the supply in

order to meet demands (American Water Works Association, 2009). In general water

has been under-priced leading often to the abuse and inefficient use of the resource

(Kingdomet al.,2006).Given that supply is likely to diminish, and the inception of new

sources for most Cities is an expensive option, as evident by the delay in the

construction of the Gwayi-Shangani Pipeline, a strong need has arisen to explore


4

different water management strategies (Srinivas, 2001). Study will be conducted on

reduction of Non-Revenue Water (NRW) as a tool for Water Demand Management in

the CoB through the hydraulic modelling of the Magwegwe Reservoir Zone, Cowdray

Park Area so that recommendations can be suggested to the City.

1.3. Overall Objective

To quantify the amount and investigate causes of Non-Revenue Water then suggest

reduction mechanisms of Non-Revenue Water.

1.3.1. Specific objectives

The study’s specific objectives are:

1. To quantify the system input volume (SIV).

2. To quantify the amount of Non-Revenue Water (NRW).

3. To construct a water balance for the Cowdray Park Network.

4. To quantify amount of real and apparent losses in the network.

5. To establish location of highest losses in the system.

6. To create consumption billing database.

7. To suggest methods of night flow pressure reduction.

8. To formulate maintenance strategies or plans of the existing network.

1.3.2. Methodology

To efficiently handle data and results database creation for consumers (domestic,

industrial, commercial and fire) will be done and linked to the network layout on

Geographical Information Systems (G.I.S). This data handling method will lead to

effective and efficient execution of objectives. The particular methodology to be

employed includes:


5

Quantify the Input volume into the Cowdray Park Network

Water supply and distribution schematic diagrams will be compiled, with input obtained

from CoB personnel, showing the reservoir pipework layout inclusive of Magwegwe

Reservoir that services Cowdray Park network. The input volume will then be

calculated or derived according to the obtained data and by flow measurement at

specific points that border the Cowdray Park area.

Water Balance

An excel spread sheet software will be created so as to input the SIV, pressure and

losses values obtainable on site, this software will also give the output of the amount

of Non-Revenue water after combining or linking with billing database.

Reduction of Real losses

This loss is most effectively dealt with through pressure management, leak detection

and repair, prudent operation systems and, in extreme cases, infrastructure

replacement.Leak detection will be employed and remedial actions, such as

performance based contracts, Public Private Partnerships (PPPs) and emergency

response teams, will be applied for a period of three months then results will be

analysed against a control area where normal remedial actions, that is the reliance

on the public for leak reporting and use of council deployment for maintenance.

Pressure Management (Rezoning and Optimization)

A high proportion of the reticulation network is operating at above 60m maximum

pressure (Average Zone Pressure has been calculated to be 66m), and leaks appear

to be more prevalent in the high pressure areas. (Engineering Services, 2012).

Pressure management strategies such as introduction of Pressure reducing valves

(PRVs) will be employed after day and night pressure measurements have been


6

assessed.

1.4. Expected results

1. Quantified system input volume (SIV) and Non-Revenue Water (NRW).

2. Constructed water balance for the Cowdray Park Network.

3. Amount of real and apparent losses in the network.

4. Location of highest losses in the system.

5. Maintenance strategies or plans of the existing water supply and

distribution network and applicable strategies for real loss reduction and

water demand management.

6. NRW management software comprising of a billing database linked to

GIS network layout.

7. Strategies that lead to achieving performance indicators standards like

the attainment of an Infrastructure Leakage Index (ILI) value of close to

1, the ILI is defined as the ratio of Current Annual Real Losses (CARL) to

Unavoidable Annual Real Losses (UARL)

Timeline

Activities to be carried out are:

1. Data Collection

2. Data Analysis

3. Formulation of remedial strategies


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4. Execution of Pilot remedial actions

5. Production of Final Project

MONTH

ACTIVITY November December January February March April May

Data Collection

Data Analysis

Formulation of Remedial

strategies

Execution of Pilot

remedial actions

Production of Final

Project

Table 2.1 Activities and Timeline


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2. LITERATURE REVIEW

2.1. Water Conservation and Demand Management

Water conservation and water demand management are often used as synonymous

terms. Although the meaning and implications of these terms is very similar, it is

important to recognise the difference.

In terms of non-revenue water reduction Water Demand Management requires a

paradigm shift as shown in figure 1.1, moving to an approach that considers all

issues in a holistic way.

SUPPLY DRIVEN

How much water is

Pumped into the system?

DEMAND DRIVEN

How much water is

Getting to the

consumers?

Figure 2.1 Paradigm shift for Water demand management (Butle 2006)

2.1.1. Water conservation

Over time, the meaning of water conservation has varied. From the beginning of the

industrial revolution, water conservation meant dams to capture and store water so it

could be distributed as needed. These systems were designed to conserve water by

preventing the waste of water to the ocean. Over the last two decades the meaning

of water conservation became restricted to “use less water” and “protect the

environment”.


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Water conservation proposed is: “The minimisation of loss or waste, the

preservation, care and protection of water resources and the efficient and effective

use of water.”

It is important to recognise that water conservation should be both an objective in

water resource management and water services management as well as a strategy.

2.1.2. Demand management

Demand management is defined as: “The adaptation and implementation of a

strategy (policies and initiatives) by a water institution to influence the water demand

and usage of water in order to meet any of the following objectives: economic

efficiency, social development, social equity, environmental protection, sustainability

of water supply and services, and political acceptability.”

Demand management should not be regarded as the objective but rather a strategy

to meet a number of objectives. One reason why the full potential of demand

management is often not recognized is because it is often perceived or understood in

a limited context.

It is common for people to equate demand management only to programs such as

communications campaigns or tariff increases. Demand management should equate

to the development and implementation of strategies and initiatives associated to

managing water usage.

A useful comparison on the philosophy of demand management is a comparison with

the role of marketing in the commercial corporate environment. In the past marketing

in the commercial environment meant simply advertising. Currently marketing has a

much wider meaning which involves understanding the clients and their needs,

understanding the market forces and then deriving a strategy in order to set and

achieve target sales, market share and profits. The principles of demand management

are very similar to that of marketing, where the water supply institutions should set


10

water demand goals and targets by managing the distribution systems and consumer

demands in order to achieve the objectives of economic efficiency, social

development, social equity, affordability and sustainability. The water supply industry

can gain a lot by adopting marketing principles to the demand management strategies.

The scope of Water Conservation (WC)/Demand Management (DM) measures

In Southern Africa due to often complex institutional arrangements particularly in the

provision of water services, it is often difficult to distinguish what measures are

included in demand management and may vary according to which water institution’s

perspective it is viewed from. For example, the perspective of the Department of Water

Affairs and Forestry of South Africa (DWAF) in its role to manage water resources may

only include as demand management those measures that affect the overall

“consumptive” usage of water or the net water abstraction through the water supply

chain. From a Water Board’s perspective demand management will include any

measures that will reduce its total amount of water abstracted from the water source.

This will include measures to reduce losses in the purification process, the bulk

distribution system, the distribution system of the service provider and the

consumption by the end user. From a service provider’s perspective demand

management will only include measures to reduce distribution losses and the

consumption by the end consumer.

For common understanding it is proposed that the scope of demand management is

defined to include the entire water supply chain - from the point of abstraction to the

point of usage. This includes all levels of distribution management and customer

demand management. The conservation measures related to the water resources

and return flow are considered under water resource management and return flow

management respectively.


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2.2. The integrated Water Resource Management (IWRM).

The IWRM is the idea that instead of the usual sectoral approach to developing and

managing water resources, it is necessary to recognise that river basins are complex

systems, in which use of water for one purpose has important implications for other

uses.

Focusing attention on water basins (a term that includes the upper and lower areas of

the basin as well as the groundwater) enables a systematic approach, considering the

socio-economic, and human dimensions as well as the physical. Classical efficiency

considers water flowing into drains as a “loss.” But because of reuse, from a basin

perspective one person’s wasted drainage water is another’s vital source. While

efficiencies at field level may be low, in the same basin the overall effective efficiency

of a basin may be quite high, and the “real” opportunities to save water by improving

“efficiency” may therefore be limited.

This will be particularly so in the case of “closed” water systems. As population and

economic growth increase the demand for water basins evolve from being “open”

(where unused water is still available for additional uses) to being “closed” (where all

useable flows are captured and distributed). Most water basins in arid areas and many

basins even in non-arid areas are becoming closed basins. This has very important

policy implications, as noted. For example, as upstream uses reduce the quality or

quantity of flows downstream, different users become increasingly interdependent.

Managing this interdependency is an important public function, which few developing

countries are equipped to do. It is very difficult to develop effective institutional

mechanisms to manage water systems, particularly were political or administrative

boundaries do not coincide with watershed boundaries, or where competing partisan

interests are powerful and entrenched.

2.2.1. Components and Definitions of Non-Revenue Water (NRW)

In order to come to better understanding and set the framework for in-depth research

into the current topic, it was necessary to find out the various components and their

definitions as they relate to the topic. Various literatures were identified. But the one


12

which seemed to have dealt with the issue of non-revenue water to a greater extent in

recent times and to which most writers and researchers kept referring to was the

document which has been developed by the International Water Association (IWA)

Water Loss Task Forces for concepts and methodologies for quantifying and

definitions of the components of non-revenue water. Most of the following definitions

are therefore quoted from this document.

Non-Revenue Water (NRW) in a water distribution network, which has been recently

introduced by the IWA instead of Unaccounted For Water (UFW) (Farley and Trow,

2003), is defined as the difference between total inflow to the system and total

metered and authorized un-metered consumptions. NRW is divided into two parts,

apparent and real losses. Apparent losses include human, management and metering

errors and lead to consumption of water without charging. Real losses are some

amount of water which is wasted from the network. Real losses are categorized to

water losses from reported an unreported bursts, background losses, reservoir

leakage and overflow and leakage from valves and pumps. The components of NRW

are determined by a field study with investigation of all properties in the study area

and all the components of water distribution network (such as reservoir, pumps, valves

and pipes).

The main contributors to NRW as depicted in figure 1.2 are thus:

1. Un-billed Authorised Consumption includes water used by the utility for

operational purposes, water used for fire fighting, water used to scour

lines, clean reservoirs, fill lines after repairs. Can also include

unmetered public standpipes, or unbilled services to informal areas, and

water provided for free to certain consumer groups.

2. Apparent or Commercial loss (water that is used but not billed) such as

under-reading meters, incorrect meter readings, data-handling errors,

and theft of water in various forms.

3. Physical or Real loss comprises leakage from all parts of the system

through bursts and leaks and reservoir overflows at the utility’s storage

tanks. These occur as a result of poor operation and maintenance, the

lack of active leakage control, and poor quality of underground assets

and appurtenances. It is “any leakage downstream of a production


13

source and upstream of the consumer revenue meter” (UNEP/IETC

1999:221)

WATER SUPPLY

SYSTEM

Own sources

Water imports

Water exports

Billed consumption

Unbilled consumption

Apparent Losses

Real Losses

Figure 2.2. Component of Non-Revenue Water (Liemberger, 2005)

2.3. BURST AND BACKGROUND LEAKS.

In the course of the UK research into leakage management the leaks found in any

water supply system were split into two types – those large enough to warrant serious

attention with regards to location and repair and those too small to warrant such

attention. The larger more serious leaks that warrant direct attention are referred to

as bursts while those too small to deserve such attention are referred to as background

leaks. The threshold between bursts and background leaks is not fixed and can vary

from country to country. In the UK a threshold limit of 0.5 m3/h is used while in South

Africa a lower limit of 0.25 m3/h is adopted. In other words:

Leaks > 0.25 m3/h = Bursts

Leaks < 0.25 m3/h = Background Leaks


14

In all water supply systems there are likely to be both bursts and background leaks

since it is not possible to develop a system completely free from leakage.(McKenzie

et al, 2001)

2.4. WATER BALANCE

Only by quantifying NRW and its components, calculating appropriate performance

indicators, and turning volumes of lost water into monetary values, can the NRW

situation be properly understood and the required actions taken.

The first step in reducing NRW is to develop an understanding of the ‘big picture’ of

the water system, which involves establishing a water balance (also called a ‘water

audit’).

The sum of all water quantities that go into the water supply system compared with

the sum of all water quantities that leave the system. ‘Input’ minus ‘output’ should be

equal to zero.

Water losses depict the volume of water lost between the points of supply and the

customer due to various reasons. The components of NRW can be determined by

conducting a water balance. This is based on the measurement or estimation of water

produced, imported, exported, consumed or lost – the calculation should balance. The

water balance calculation provides a guide to how much is lost as leakage from the

network (‘real’ losses), and how much is due to ‘apparent’ or non-physical losses.

Because of the wide diversity of formats and definitions used for water balance

calculations internationally (often within the same country), there has been an urgent

need for a common international terminology. Drawing on the best practice from many

countries, IWA Task Forces on Water Losses and Performance Indicators have

produced an international best practice approach for water balance calculations,

including definitions of its components, and for comparing performance between utility

operators.

This process helps utility managers to understand the magnitude, sources, and cost

of NRW. The International Water Association (IWA) has developed a standard

international water balance structure and terminology that has been adopted by

national associations in many countries across the world (Figure 2.3).


15

System

Input

Volume

Authorised

Consumption

Billed Authorised

Consumption

Billed Metered

Consumption

Revenue Water

Billed Unmetered

Consumption

Unbilled Authorised

Consumption

Unbilled Metered

Consumption

Non-Revenue

Water(NRW)

Unbilled Unmetered

Consumption

Water Losses

Apparent Losses

Unauthorised

Consumption

Metering

Real Losses

Leakage on

Transmission and/or

Distribution Mains

Leakage and

overflows on storage

facilities

Leakage on service

connections

Table 2.1 Standard Water Balance format (IWA, 2003)

2.5. INTRODUCTION TO BURST AND BACKGROUND ESTIMATE (BABE) CONCEPT

In 1991, a National Leakage Initiative was established in the UK by the Water Services

Association and the Water Companies Association to update and review the

guidelines concerning leakage control that had been in use since 1980. It was agreed

by all organisations involved in potable water supply that the guidelines required

updating in view of the considerable progress that had been made over the previous

ten-year period. As a result of new water legislation, it became necessary for all water

suppliers to demonstrate to the regulators that they fully understood their position on

leakage. This did not imply that all water suppliers had to demonstrate the lowest


16

achievable leakage levels, but simply that they were applying correct and appropriate

economic and resourcing principals. To this end, it was agreed that all water suppliers

would adopt a straightforward and pragmatic approach to leakage levels. This was

achieved through the development of various techniques that became known as the

Burst and Background Estimate (BABE) methodology.(Lambert A, 1994)

The BABE procedures were developed over a period of approximately four years by

a group of specialists selected from several of the major water supply companies

based in England and Wales. The group was instructed to develop a systematic and

pragmatic approach to leakage management that could be applied equally well to all

of the UK water supply utilities. The result of this initiative was a set of nine reports

published by the UK Water Industry (WRc) on the subject of managing leakage. The

nine WRc reports cover the following topics:

Report A: Summary Report, Report B: Reporting Comparative Leakage Performance,

Report C: Setting Economic Leakage Targets, Report D: Estimating Unmeasured

Water Delivered, Report E: Interpreting Measured Night Flows, Report F: Using Night

Flow Data, Report G: Managing Water Pressure, Report H: Dealing with Customers

Leakage, Report J: Leakage Management Techniques, Technology and Training.

The intention of the reports was not to be prescriptive, but to provide a “tool kit” to the

water industry to enable the water supply manager to evaluate leakage levels and to

manage the system.

In order to address leakage it was considered necessary to first understand the various

components making up the water balance for a typical water supply network. The

previous approach as shown in figure 2.3` was to consider three main components,

namely: Authorised metered, authorised unmetered and the remainder which

represents all unaccounted-for water, and is often referred to as the real and apparent


17

losses. Further details on real and apparent losses are provided later in this section

and are also shown in figure 2.5.

Figure 2.3. Traditional Water Balance (McKenzie, 2002)

In view of the large portion of the traditional water balance that was usually

represented by the real and apparent losses, the whole water balance approach was

revised by breaking the balance down into smaller components that could either be

measured or estimated. In this manner it was possible to gain a greater understanding

of the different components and also of their significance to the overall water balance.

A typical example of the BABE water balance is provided in Figure 1.4. It should be

AuthorisedUnmeteredDelivered

Authorised Metered

Delivered

Real and Apparent Losses


18

noted that the water balance need not be restricted to the components shown in this

figure and conversely it can be split into a greater number of components or perhaps

different components. Every system is different and it is the general approach that

should be applied and not a specific and rigid framework.(Lambert A, 1994)

Figure 2.4. BABE Water Balance Approach (McKenzie, 2002)

The BABE water balance approach has now been widely accepted worldwide and is

also incorporated in much of the latest South African water legislation. It is not a highly

technical or complicated approach; on the contrary, it is extremely simple and logical.

The typical components that can be included in any particular water balance were

established at the International Water Supply Association Workshop held in Lisbon in

May 1997. The water balance components identified at the workshop are shown in


19

figure 2.5. It should be noted that the components shown in this figure also include

the losses associated with the bulk water system as well as the purification system.

For municipalities supplying only the water on the distribution side of the bulk supply

system, many of the items shown in figure 2.5 can be omitted. Similarly, in many of

the municipalities in South Africa, the internal plumbing losses (LP) dominate the

whole water balance although such losses are represented by only a small block in

the figure. In such cases it may not be necessary to undertake a full and detailed

water balance until the plumbing losses are under control.

Figure 2.5 Recommended BABE Water Balance Components (Lambert, 2002)

Figure 1.5 provides a breakdown of the most important components that can be

included in a water balance for a specific water supplier. It is important to note that

the losses have been broken down into real and apparent losses. Real losses are

those where the water has in fact left the system and has not been utilised in any way.

If such losses can be reduced, the total water required by the supplier will also be

reduced. Apparent losses on the other hand are simply “paper” losses that do not


20

represent a loss from the system. They are usually due to illegal connections, and

meter and billing errors. If such losses are eliminated, the total water required by the

supplier may not change, however, the “unaccounted-for” component in the water

balance will be reduced. In such cases certain other components such as “authorised

metered” or even “authorised unmetered” will increase as the apparent losses are

reduced.(Bhagwan 1995)

2.6. IMPACTS OF NRW: THE VICIOUS AND VIRTUOUS CIRCLES.

The ‘Vicious Circle’ of NRW (Figure 2.7) is one of the key reasons for poor company

performance and results in both physical and commercial losses. Physical losses, or

leakages, divert precious water from reaching customers and increase operating

costs. They also result in larger investments than necessary to augment network

capacity. Commercial losses, caused by customer meter inaccuracies, poor data

handling, and illegal connections, reduce income and thereby financial resource

generation.

WATER UTILITY NEEDS TO

MEET INCREASING DEMAND

WATER UTILITY RECEIVES

LESS REVENUE HENCE

REDUCED EXPENDITURE

NRW

INCREASES

THE VICIOUS NRW CYCLE

Figure 2.6 The Vicious NRW cycle (Farley, 2003)


21

The challenge for water utility managers is to transform the Vicious Circle into the

‘Virtuous Circle’ (Figure 2.8). In effect, reducing NRW releases new sources of both

water and finances. Reducing excessive physical losses results in a greater amount

of water available for consumption and postpones the need for investing in new

sources. It also lowers operating costs. Similarly, reducing commercial losses

generates more revenues

WATER UTILITY RECEIVES MORE

REVENUE AND FINANCIAL

CAPACITY

WATER UTILITY INVESTS IN

NRW REDUCTION

NRW

REDUCES

THE VIRTUOUS NRW CYCLE

Figure 2.7 The Virtuous NRW cycle(Farley, 2003)

2.7. STRATEGY FOR DEALING WITH WATER LOSSES

The two most important components of NRW are the real losses and the apparent

losses. These components are the ones which need much resource in terms of

logistics, staffing and finance in order to control water losses. The third component,

unbilled authorised consumption can be controlled fairly well without much resource.

It is therefore important to develop the appropriate strategies for controlling water

losses especially through real and apparent losses if meaningful achievements are to


22

be made and the outcome would justify the efforts put in. The starting point to deal

with water losses in any water utility, according Butler and Mamon (2006:143), is to

understand the network system of the utility.

Butler and Mamon (2006:143), suggest that certain questions should be posed about

the water utility with regard to the characteristics, the production process, and the

operating practices, and using the available tools and mechanisms within the water

utility to answer these questions form the first step in the right direction to deal with the

prevailing situation.

In the process of trying to answer these questions, better understanding of the network

system of the water utility would now be obtained, which would then form the basis for

the formulation of strategies for dealing with water losses.

Butler and Mamon (2003:143) suggest the following questions:

1. How much water is being lost?

2. Where is it being lost from?

3. Why is it being lost?

A few methodologies have been developed to assess the NRW in water distribution

systems, however most of them just concentrate on the real losses concept, and have

no emphasis on the apparent losses, which is so important in most undeveloped and

developing countries.

As a pioneer, WRc (1980) published the Report 26 in which a methodology to

determine the UFW and leakage was included. After a decade and based on

comprehensive summarizing of many case studies, Report 26 was revised by the UK

Water Industry (1994). As an output, nine reports were published on leakage

management concept. At the same time, some research results were presented to

Leakage 2005 - Conference Proceedings where a Software Tool for Non-Revenue

Water Calculations in Conjunction with Hydraulic and GIS Models was introduced with

new methodologies and terminologies for better understanding of the leakage

components.


23

Lambert (1994) and May (1994) presented the concepts of bursts and background

losses estimation (BABE) and Fixed and Variable Area Discharge (FAVAD),

respectively. These two concepts were applied in many countries to resolve the

problem, regarding real losses and leakage management. Several models have been

developed to evaluate real losses and leakage management schemes, which mostly

investigate the leakage calculation, pressure management, optimal leakage level, etc.

A list of these models can be obtained from Asadiani (2004). Recently a few software

for leakage modelling have been developed which are described as follows.

1. SANFLOW model (Mackenzie, 1999) uses the Minimum Night Flow (MNF)

method based on the inflow measurement at the MNF time. This model suffers

from two major shortcomings. First one is use of estimated values for reported

and unreported bursts and the second one is calculation of the total daily

leakage by multiplying the leakage rate at the MNF time by 24. However, it is

clear that arithmetic average cannot represent the total daily leakage,

realistically.

In this approach, the minimum night flow is considered to consist of three

main components namely:

Normal legitimate night use

Background losses

Burst pipes.


24

Figure 2.8 Breakdown of night flow (IWA, 2003)

Normal domestic night use

Normal domestic night use represents the water used during the night in a

household and is predominantly due to toilet use. Use of water for making

coffee or tea represents a very small portion of the overall household use and

is effectively ignored. In some areas of South Africa, garden watering or the

filling of swimming pools may be of importance, however, in most cases such

water use is minimal between the hours of 00:00 and 04:00 when the night-flow

monitoring is undertaken.

Experience in various parts of the world has shown that approximately 6% of

the population are active (POPACT) during each hour and that the water use is

in the order of 10 l /head.h (POPUSE). POPACT is expressed as a percentage


25

of the population (POP) and should not be confused with the number of

properties. The value of POPUSE is based on a standard 10 l toilet cistern and

may vary from one country or region to another. The normal household night

use is therefore easily estimated from the product of the active population (i.e.

POPACT * POP) and the average use per hour (POPUSE).

HNORUSE = (POPACT * POP) * POPUSE

From various studies undertaken in different parts of the world it is suggested

that the normal household use is based on either 1.7 l per household per hour

or 0.6 l per person per hour (WRc, Report E).

Background leakage

Background leakage is the cumulative leakage from all relatively small leaks

and seepage that are individually less than 250 l/h at 50 m of pressure. Such

leaks occur from valves, joints, hydrants, stop-taps, meters, dripping taps, toilet

cisterns, roof tanks etc. Individually such leaks are generally uneconomic to

find and repair with the result that background leakage is accepted as a fact of

life within certain limits.

In general, background leakage can be split into three main components

namely:

Background leakage from mains (BLMAIN)

Background leakage from connections (BLCONN)

Background leakage from installations (BLINST)

Background leakage from mains (BLMAIN)

There will always be some Background Leakage from any distribution system,

some of which occurs from the water mains. Small leaks often occur at the pipe

joints or from small cracks or holes in the pipes and the magnitude of the


26

leakage is dependent upon the condition of the infrastructure and the operating

pressure.

For the purpose of the background night flows model, all process parameters

are given at the standard operating pressure of 50 m with the result that the

parameter describing the background leakage from mains (BLMAIN) varies

only with the condition of the infrastructure. Suggested values from the WRc

Report E indicate an average value of 40 l/km of mains per hour with a range

of 50 % (that is. 20 l/kmh to 60 l/kmh).

Background leakage from connections (BLCONN)

Poor workmanship coupled with general wear and tear often results in leaks

from pipe connections. In general there will be one pipe connection to each

property and the background leakage from connections (BLCONN) is therefore

expressed as an average loss per connection where the number of connections

is usually estimated directly from the number of properties. Connection leakage

is considered as the leakage occurring from the connection at the water main

to the water meter at the property or to the property boundary in cases where

no meters exist. In most water distribution systems, the connection losses are

often the major source of loss from the system.

Suggested values of background leakage from connections are provided in the

WRc Report E

l/proph to 4.5 l/proph) depending on the condition of the infrastructure.

Background leakage from installations (BLINST)

The installation refers to all pipe-work, plumbing, fittings and fixtures both inside

and outside the building located on the consumer side of the billing meter. It

does not include the meter that generally remains the property of the water

supply utility.

A certain portion of background leakage occurs on the individual properties from

either the pipe entering the dwelling from the water meter or from the various


27

plumbing fittings inside the building. In most cases such leakage will be lower

than that occurring from the mains connection (as discussed in the previous

section). In South Africa, however, there are occasions where the leakage from

the installations is dominant and in fact represents the largest form of leakage

from the system.

Unless more reliable information is available to suggest higher (or lower)

leakage rates, the value recommended in the WRC Report E (Table 4.1) is 1.0

l per property per hour with a range of 50 % (i.e. 0.5 l/proph to 1.5 l/proph)

depending on the condition of the infrastructure. The leakage is usually

assumed to be equally divided between the pipe from the meter to the building

and the internal plumbing fittings.

2.7.1. Calculation of bursts

Having measured or estimated the various components of normal night use and

background night use, the two figures are added together and then subtracted

from the measured minimum night flow. The difference is the unexplained

losses that are attributable to either unreported bursts or to errors in the

assumptions made during the calculation. The possibility of errors in the

assumptions will be dealt with separately and the remainder of this section will

consider the difference to be leakage.

2.7.2. Pressure correction

One of the most important factors influencing leakage is pressure.

Considerable work has been undertaken over the past 10 years in many parts

of the world to establish how leakage from a water distribution system reacts

to pressure.

It is generally accepted that flow from a hole in a pipe will react to pressure in

accordance with normal hydraulic theory that indicates a square root power

relationship between flow and pressure.


28

FlowP2 = FlowP1 x PCF where:

P1 = Pressure 1 (m)

P2 = Pressure 2 (m)

FlowP1 = Flow at pressure P1 (m3/h)

FlowP2 = Flow at pressure P1 (m3/h)

PCF = Pressure correction factor = (P1/P2) POW

pow = power exponent.

This implies that if pressure doubles, the flow will increase by a factor of 1.4

(i.e. PCF = 2 0.5). This has been tested and found to be realistic irrespective of

whether the pipe is above ground or buried. The problem arises because in

many systems the leakage has been found to react by a factor greater than 1.4.

This has caused considerable debate and confusion especially when trying to

establish the likely savings through pressure reduction measures.

Although there are still various opinions concerning the explanation for the

larger than expected influences of pressure on leakage in many systems, at

least one plausible theory has been suggested. In 1997, John May in the UK

first suggested the possibility of fixed area and variable area discharges

(FIVAD). He carried our considerable research on this topic and has found that

systems will react differently to pressure depending upon the type of leak being

considered. If the leak is a corrosion hole for example, the size of the opening

will remain fixed as the pressure in the system changes on a daily cycle. In

such cases, the water lost from the hole will follow the general square root

principle as outlined above. This type of leak is referred to as a fixed area leak.


29

If, however, the leak is due to a leaking joint, the size of the opening may in fact

increase as the pressure increases due to the opening and closing of the joint

with the changing pressure. In such cases the flow of water will increase by

much more than the fixed area leak. Research suggests that in such cases, a

power exponent of 1.5 should be used instead of the 0.5 used for the fixed area

cases. This suggests that if the pressure doubles, the leakage will increase by

a factor of 2.83 (i.e. PCF = 21.5).

In the case of longitudinal leaks, the area of leak may increase both in width as

well as length as is often the case with plastic pipes. In such cases the power

exponent can increase to 2.5. In other words, if the pressure doubles, the flow

through the leak will increase by a factor of 5.6 (i.e. PCF = 2 2.5).

The problem faced by the water distribution engineer is to decide what factor

should be used when estimating the influence of pressure on leakage flow. In

general, it is recommended that a power exponent of 0.5 should be used for all

burst flows since a burst pipe is usually a fixed area discharge. In the case of

the background losses, however, the leaks are likely to be variable area

discharges in which case a larger power exponent should be used. A power

exponent of 1.5 is usually used for the background losses, which is considered

to represent a collection of leaks that have factors of between 0.5 and 2.5. If

all of the pipe work is known to be plastic, a higher value may be appropriate

and conversely, if the pipes are made from cast-iron, a lower value (e.g. 1.0)

should be used.

The influence of the power exponent used in the analysis can be seen in

Table 3.1 where the factors given relate to a basic pressure of 50 m. From

the Table it can be seen that if the pressure is reduced from 50 m to 20 m, the

leakage will decrease to 0.25 of the original value, i.e. a four-fold reduction in

leakage.

2. PRESMAC model (Mackenzie, 2001) is applied for pressure management

purposes. As a disadvantage, this model does not use any hydraulic model and


30

pressure is calculated with some simplifications which lead to high uncertainty

especially in complex networks.

3. ECONOLEAK (Mackenzie and Lambert, 2002) calculates real losses using the

annual water balance method in which, apparent losses are considered as a

percentage of total NRW. Then using the BABE concept, the leakage

components are evaluated. Therefore, it just uses estimated values to calculate

the NRW components.

1. BENCHLEAK model (Mackenzie et al., 2002) was written in an excel

environment to calculate the NRW components using the water balance

method. To resolve the abovementioned weaknesses of the existing leakage

models, this paper aims to develop comprehensive software to evaluate both

apparent and real losses and their components. The model is able to be linked

to hydraulic and GIS models to determine values of nodal and pipe leakage.

The results can be represented in the GIS environmental to perform further

analyses by decision makers


31

3. STUDY AREA

3.1. Introduction

The Cowdray Park high density area that covers an area of 16,5km2 lies in the North

Western part of the City of Bulawayo as depicted in Annexure A; it was developed in

the year 1992 after the need for housing increased in the City. This area was ideal for

study due to the existence of all the parameters required to study Non-Revenue water,

these are inclusive of–

Illegal connections.

Above average, frequent and high rate bursts.

New developments by private developers.

Lack of a complete billing database that then leaves more research to be done.

The description of the area is given according to values obtained from Google earth,

ArcGIS 10.1 and drawings acquired from the Bulawayo City Council. Summary

description of the area is given in the table below.

PARAMETER VALUE

Estimated Population 64 500 people

Total Properties 21 500 properties

Properties connected to water system 8 566 properties

Area 16,5 km2

Total length of distribution network 147,38km

Average consumption 7 704,5m3/day

Figure 3.1 Summary Description of Cowdray Park Area


32

3.2. Water distribution system in Cowdray Park

The distribution system (total 147 380 km mains and distribution pipework) consists of

pipes from 50 to 600 mm. 80 % of the pipes are made from Polyvinyl Chloride (PVC)

the remaining pipes are asbestos cement (AC) and steel, both galvanised and bitumen

coated.

The primary distribution system and trunk mains are of diameter 300 – 600 mm. The

primary distribution includes interconnection between the ring mains, which are

located around the area. The system is very complicated and difficult to understand

and operate since it was designed and constructed by numerous Contractors. The

reservoir level at Magwegwe (the supply for Cowdray Park) can be read remotely by

an old system using telephone lines and manually dialling each reservoir, but for this

exercise an insertion meter was used to obtain the reservoir level.

3.2.1. Service pipelines

Consumers are connected to the distribution system through service pipelines.

Domestic meters are fitted on the service pipeline to measure the consumption to each

consumer. The part of the service pipeline from the main distribution pipe to the meter

is the responsibility of Bulawayo City Council. Repair of leaks and replacement of

these service pipelines have to be carried out by BCC. The part of the service pipeline

from the meter to the house installations is private, and the responsibility of the house

owner.

In the high density areas the meter is normally fitted near the house or on the wall of

the house. Council is therefore responsible for the total service pipeline crossing the

private plot to the house, normally 10-18 m.


33

.

3.2.2. Present water supply situation

Due to the precipitation received, the precarious situation for Bulawayo water Supply

has been alleviated. The current volume in the dams is 78 % of the total full capacity

(current dam storage is 306,118,957 m3). This will cover the water demand for

approximately 37 months provided the specific consumption per person does not

increase.

However, there should not be a feeling of complacency. The good rainy season has

given BCC some needed time to implement water conservation measures so

Bulawayo will be better prepared for years with much less rainfall.

Figure 3.2: Water Disribution in Cowdray Park


34

3.2.3. Existing water supply Water system and Water sources

The water sources in Bulawayo consist of 6 dams at the Southern Catchment and a

groundwater scheme of 68 boreholes commissioned in 1993. Annexure A shows the

Water Sources and the Primary system in Bulawayo.

The present total capacity of Bulawayo’s water supply dams is approximately414

million cubic meters. Traditionally dam yields for raw water abstraction in Zimbabwe

have been based on the 4% yield principle. Effectively by this means that the dam is

assessed to provide an abstraction rate equal to or above the nominated yield for 96

years out of 100.

All of Bulawayo’s water supply dams are in the Southern Water Catchment Area

(Matabeleland South) are characterised by average rainfall of 594 mm per year.

However, the catchment area has experienced repeated droughts the last 25 years

and is therefore relying on the storage capacity of the water.

Nyamandlovu Aquifer-The groundwater supply from the Nyamandlovu aquifer was

established as an emergency drought relief project in 1992 to ease the supply situation

when the water supply sources was on the verge of drying up. Total installed well

capacity at Nyamandlovu is 25,000 m3/d of underground water. However, later

assessment of the aquifer concludes that the abstractions from the current well field

should be restricted to 9000 – 12000 m3 per day to preserve its long term integrity.

3.2.4. Short term extensions of the water sources

The Mtshabezi dam was constructed in 1994, it has been connected to the water

supply system. A pipeline connection from this dam to the Mzingwane pipeline to

Ncema Treatment works exists. This provides an average of 7 000 m3per day in the

stead of the proposed capacity of 17ML.

At the Nyamandlovu aquifer investigations are underway with the aim of extending the

well field to the north west of the current one to bring the production up to the capacity


35

of the Nyamandlovu – Bulawayo pipeline of 26 000 m3 per day. Ten deep boreholes

have been drilled and are being pump tested to determine their safe yields. The

boreholes will be connected to the existing network.

3.3. Water Treatment

The water treatment plants Criterion and Ncema have today an estimated capacity of

respectively 181,000 and 30,000 m3/d, a total of 211.000 m3/d.

Both Ncema and Criterion has a treatment process consisting of:

1. Pre pH correction using lime (rarely used)

2. Flocculation using alum and polyelectrolyte

3. Clarification

4. Rapid sand filters

5. Disinfection by chlorination and chloramination (ammonia)

6. Post pH correction using lime (rarely used)

For additional disinfecting chlorine is added at the reservoirs Tuli, Magwegwe and Rifle

Range.

The water treatment plants are in fairly good condition, but some equipment at Ncema

is out of order.

3.4. Water delivery facilities

Southern Catchment-The Southern Catchment has the following basic delivery

facilities:

1. Treated Water Pumping Main from Ncema Waterworks to Tuli Hill reservoir that

will convey 83,000m3/d.


36

2. Twin Raw Water Pumping Mains from Ncema Dam to Criterion Waterworks;

that will convey 180,000 m3/d.

The delivery facilities are designed normally to convey the average daily flow in a Peak

Week (usually in November). Bulawayo have mitigated this demand in part by

constructing a large raw water reservoir at Criterion Waterworks.

Northern Catchment-The abstracted water from the Nyamandlovu aquifer is pumped

to the Bulawayo water distribution system in two steps, one pumping station at

Rochester near the well field and the next station at Cowdray Park. The capacity of

the water transmission system is 26 000 m3 per day.

A schematic presentation of the existing water delivery facilities including the

reservoirs and the main trunks is showed in Annexure B.

3.5. RESERVOIRS

The water reservoirs in the system are as follows:

Treated water reservoirs and respective capacities:

Hillside 45,000m3

Magwegwe 108,000m3

6 J 45,000m3

Rifle Range 67,500m3

Criterion 90,000m3

Tuli Hill 90,000m3

Woodville 2,250m3

Total treated water storage 447,750m3

Raw Water Reservoir:


37

Criterion- 1,400,000 m3

Reservoirs are required for two primary reasons:

1. To supply excess consumption on peak days compared with supply capacity of

peak week.

2. To provide supply continuity in the event of power failures

Bulawayo has a treated water reservoir storage capacity of 4 –5 days of Treatment

Works Annual Average Daily Consumption. This is more than normal design in similar

systems, and thus regarded as sufficient. The condition of the reservoirs needs to be

checked.

3.6. Pressure Zones

The distribution system for Bulawayo is divided into approximately 30 pressure zones

supplied from the reservoirs and using pressure reducing valves (PRV’s) to set the

pressure in each zone. The pressure reducing valves in the network are of size 100

mm to 400 mm.

In addition there are 8 booster pumping stations serving the high level areas

surrounding the reservoirs. In absence of the hydraulic network model the operational

staff control the pressure zoning in an ad hoc manner.

The pressure zoning is not optimal and a new structured pressure-zoning plan has to

be established early in the work program. The difference in elevation of the supply

areas is 200 m and many zones will be required to maintain pressure at the level of 2

–3 bars in residential areas and 4 –6 bar in the city areas.

The city currently operates passive leakage control although active methods were

employed for the purpose of this project.

The meter readers from the Billing section (City Treasurers Department) read the

meters every month.


38

The records of repairs to water mains obtained for Cowdray Park in the past 6 months

of 2013-2014 show the following:

Bursts on Mains No’s

50mm 12

75mm 50

100mm 39

150mm 27

225mm 12

Stopcocks and service lines 332

Valves 10

Hydrants 58

Total (6 months) 540

Leaks in service lines of galvanised steel (GI), 88% of the repairs due to corrosion of

GI pipes. Changing to other material for service pipes (polythene) should therefore be

considered. The entire system operates at 24-hour full pressure.

3.7. Water Meters

Meters are of vital importance in a water supply system both for operation of the

primary system and in leakage control operation.

The Cowdray Park area exists as a District Metered Area (DMA), implying it has its

own meter and pressure reducing valve (PRV) that is not linked to any other area and

about 7 553 consumers are metered. The water workshop has two testing facilities for

small and large meters. The smaller meters up to 50 mm are of rotary piston type and

larger meters are of the turbine type.


39

4. METHODOLOGY

4.1. STUDY DESIGN

The research methodology involves the assessment of the water distribution system

of the Cowdray Park area. This distribution system constitutes the water sources that

supply Cowdray Park and their corresponding conveyance pipelines and

appurtenances associated with this supply network. Various parameters were

quantitatively determined inclusive of pressure, flows and water losses.

4.1.1. Project Activities

The Project’s activities are grouped as follows:-

Desk studies- This involved the collection of primary data on quantity of water

supplied to the area and the billing data (showing the consumption per month

and respective amounts charged) from the local authority’s files and records.

Field studies- This encompassed carrying out interviews with key personnel

involved with running the water distribution system at the Bulawayo City

Council. It included an assessment of the distribution network, obtaining

pressure and flow data utilising the Data Logger (Sensus, undated).

Data Analysis-Quantitative data from the desk studies and field studies is

analysed.

4.1.2. Sources of Data

The data sources for the network layout, study area and information regarding the

losses are:

The Water Branch files containing reports regarding the distribution network

and developments in Cowdray Park

Water books and drawings from BCC.

Documents and reports from the BCC water workshops


40

Various documents and reports prepared by other companies and institutions

on the subject of Non-Revenue Water on and for the City of Bulawayo.

Field Flow and pressure measurements made during the current project

Billing Database from the Billing section of Bulawayo City Council that shows

the total number of households being billed for the water utilised and the

revenue collected therein.

4.2. Sampling plan

One of the goals of the research was to obtain a quantitative analysis of the non-

revenue water brought about by the three NRW contributors (Real and apparent

losses and Unbilled authorised consumption). To meet this objective a sampling plan

was developed. The questions raised in the sampling plan were:

1. From where within the target population should samples be collected

2. What type of samples should be collected

3. How many samples should be analysed

The Cowdray Park area which has a total number of 22 686 units being billed was

divided into 6 sub areas by the method of stratified sampling according to the

Contractors who designed and installed the water reticulation system and these are:

Hawkflight (2 500 units)

Glencoe (1 300 units)

The Government (Garikai/Hlalani Kuhle) (6 050 Units)

Bulawayo Home Seekers Consortium Trust (BHSCT) (3 300 Units)

Bulawayo City Council (8 490 Units)

Other developers (1 046)

These formulated strata were further sampled systematically for more data to be

collected like meter tests, pressure tests and state of connection at individual

connections.


41

For this purpose simple random sampling technique was adopted for a 95%

confidence interval (Farley, 2008). This is to give 95% representation of the total

population this is so because a sample giving 100% confidence was not feasible with

regards to the time frame and the availability of resources or their lack thereof.

𝑛 =𝑁

1 + 𝑁𝑒2

Yamane (1967:886)

The above formula was used to calculate the sample sizes in Tables 4.1 below

Where n: Sample size

N: Total population

e: level value of precision

Size of Population Sample Size (n) for Precision (e) of:

±3% ±5% ±7% ±10%

500 a 222 145 83

600 a 240 152 86

700 a 255 158 88

800 a 267 163 89

900 a 277 166 90

1,000 a 286 169 91

2,000 714 333 185 95

3,000 811 353 191 97

4,000 870 364 194 98

5,000 909 370 196 98

6,000 938 375 197 98

7,000 959 378 198 99

8,000 976 381 199 99

9,000 989 383 200 99

10,000 1,000 385 200 99

15,000 1,034 390 201 99

20,000 1,053 392 204 100


42

25,000 1,064 394 204 100

50,000 1,087 397 204 100

100,000 1,099 398 204 100

>100,000 1,111 400 204 100

a = Assumption of normal population is poor (Yamane, 1967). The entire population

should be sampled.

Table 4.1 Sample sizes (Yamane, 1967)

4.3. Flow measurements

Accumulated field flow measurements in Cowdray Park were carried out using

PrimeLog and Sensus Data Loggers which were installed with assistance from

Bulawayo Council staff on Pressure Reducing Valves and meters as shown in figure

4.1(a) and (b) below. Each Logger was read for a minimum period of 48 hours

recording cumulative flow records and existing pressure. It also recorded the Minimum

night flow (MNF) and hourly peaks.

Figure 4.1 Flow and pressure measurements in a PRV using a DataLogger


43

4.4. Pipeline Survey

Pipeline surveys were carried out and a combination of visual inspection and sounding

of the systems was used to find leaks where flow and pressure measurements

indicated losses. Tasks performed during the pipeline survey:

Inspection of the distribution system for visual leaks

Used listening devices (Farley, 2008) to locate and pinpoint leaks with assistance

from Bulawayo council staff.

Observed leaks were repaired

4.5. House inspection

A door-to-door survey was carried out at selected sampling households, physical

inspection of various installations and leaks and wastage were identified. Wastage

was defined as the case where water is lost due to negligence on the part of the

consumer (leaking taps, open taps, watering etc.)

Tasks performed during inspection included:

Examination of service pipelines for visual leaks by walking along the pipelines.

Inspection of water meters and stopcocks for leaks.

Inspection of household plumbing including water taps for leaks.

Examination of water storage tanks and overhead storage tanks for leaks or

malfunctioning float valves causing overflow of tanks.

Testing water meters using a portable test meter for functionality and accuracy.


44

Figure 4.2 Flow and pressure measurements in households

4.6. System inventory

A system inventory was developed using information from Engineering Services

Department (maps, information from engineers, foremen, plumbers, etc.) and the

billing system in conjunction with field survey work. Data collected includes number

of households, the type, size and length of distribution pipes, number of valves (main

and service), fire hydrants, this data was utilised as input into SANFLOW and Aqualite

softwares to give the amount of Non-Revenue water and its various contributors .

4.7. Non-Revenue Water calculation

Combination of the Top-Down and Bottom-Up approaches were applied with the

utilisation of existing softwares (Farley, 2008)

Top-Down approach starts from the water distribution system input point (since

the Cowdray Park area is a discrete District Metered Area it therefore contains


45

a Pressure Reducing Valve (PRV) and a meter hence flow and pressure were

measured at this point), to the consumer point.

In this approach the System Input Volume was determined then the route of water flow

was traced to the premises that obtain the highest and lowest pressures, respectively.

Leaks and bursts along the route were determined and water lost was quantified by

measuring flow before and after the leak or burst per unit time. This facilitated the

quantification of real losses.

Bottom-Up approach relies on the minimum night flow (MNF). This is because

during the night period the real losses are at their maximum percentages of the

total flow evident by the drop in pressure due to water loss since minimal or no

water is used by the consumer. This approach starts from the consumer

working up to the water distribution system input point by measuring the

pressure at consumer point and input point then asses any pressure reduction

along the network to locate the leaks.

The total households billed were queried utilising the database of domestic and

commercial consumers and their respective amounts paid to the Billing Section

at BCC to facilitate the quantification of apparent losses.

Metering inaccuracies were determined by taking meter readings showing the

amount of water being consumed during the study period by the households

and meter tests to determine the functionality and accuracy of the meters.

Although the whole area was not covered in this respect, appropriate samples

were taken according to the sampling methods articulated later in the chapter.

Utilising the data of households billed for water and revenue obtained from the

billing section, households that use water but are not in the database were

investigated to reveal the illegal connections that relate to the unauthorised

consumption.


46

4.7.1. Softwares

Values from field measurements were taken to be inputs to numerous Water Demand

Management softwares. Softwares utilised include:

Aqualite (Lambert) - creates a water audit for a specific water supply system. The

model was used to create an annual water balance based on the available network

data and the breakdown of the water that can be accounted for by the supplier as

authorised consumption. It provides a selection of performance indicators (ILI and

Financial indicators) which were used to evaluate the levels of leakage as well as the

effectiveness of the management of the system in terms of NRW reduction.

Sanflow (Lambert) -the South African Night Flow Analysis Model assists in the

determination of the level of leakage in a particular District metered area (DMA) from

the analysis of recorded minimum night flows.

Inputs

Column 1 contains a reference name or number for each specific night-flow analysis.

The reference is input to the model through the VARIABLES menu.

Date

This column contains the date for the specific night-flow analysis and is also input

through the VARIABLES form.

Average Zone Night Pressure (AZNP)

This column contains the measured or estimated average zone night pressure in units

of meters for each night-flow analysis. The AZNP is input to the model through the

VARIABLES form.

Measured minimum night flow

Column 4 provides the measured minimum night flow for each night-flow analysis in

units of m3/h. The value is input to the program through the VARIABLES form.


47

Background losses

Column 5 provides the total estimated background loss in units of m3/h for each night-

flow analysis. The breakdown of the background night flow can be examined by

viewing the background loss form – i.e. by clicking on the Background Loss button

(see below for details).

Normal night use

Column 6 provides the total estimated normal night use for each night-flow analysis.

Details of how the figure is calculated can be examined by viewing the Normal Night

Flow form that can be accessed by clicking the Normal Night Use button (see below

for details).

Expected minimum night flow

Column 7 provides details of the expected minimum night flow that is simply the sum

of columns 5 and 6 and represents the night flow that would occur if there are no burst

pipes in the zone.

Excess night flow

Column 8 provides details of the excess night flow in the zone and is simply the

difference between the expected minimum night flow and the measured minimum

night flow. The resulting figure is an indication of the unexplained leakage in the zone

and if a negative value appears, it suggests that there is no serious leakage problem

and that some of the base parameters have been estimated incorrectly.

Equivalent service pipe bursts

Column 9 provides an estimate of how many equivalent service pipe bursts are in the

zone for each night-flow analysis. The pressure is taken into account and this column

enables the different night-flow analyses for the zone to be compared on an equitable

basis since the variability due to operating pressure has been removed from the

calculation.


48

Outputs

Graphs can be produced showing the distribution of the various loss components over

time together with a plot of the equivalent service pipe bursts. Brief reports are also

produced for each night-flow analysis

Sensitivity analysis

Sensitivity analysis has the ability to test the sensitivity of the result to any or all of the

various parameters used in the calculation (McKenzie, 1999) The estimation of the

equivalent service pipe bursts is based on 16 different variables. These 16 variables

are generally estimated from experience, or are selected based on their default values.

In either case there is some uncertainty about the value selected for each variable.

The problem is to identify the magnitude of the uncertainty and to evaluate the

significance on the end result.

In order to quantify the uncertainty of the overall result (i.e. the number of equivalent

service pipe bursts) it is first necessary to estimate the uncertainty associated with

each of the 16 variables. Each variable can be viewed as a random variable with a

particular distribution. A normal distribution would usually be selected; however, in

this case it was decided to use a simple triangular distribution (McKenzie, 1999). The

triangular distribution was selected because it is realistic and practical, since the user

must simply supply three parameters namely:

The lower bound

The upper bound

The best estimate (as supplied through the main program).

In other words, the user must simply provide a lower and upper estimate for each

variable. Such parameters can usually be estimated based on feeling or judgment

and if the user is unsure of a particular variable, a wide range should be specified by

the user to highlight the uncertainty. For ease of use the model selected default upper

and lower bounds based on the best estimate plus and minus 20% respectively.


49

The uncertainty of the number of equivalent service pipe bursts is then quantified from

the distribution of possible values based on a computer simulation of 50 000 estimates.

In each case, a random number generator is used 16 times, once for each variable.

In this manner a random value following the particular triangular distribution is created

for each individual variable. These values are then used to produce one possible

result for the number of equivalent service pipe bursts.

At the end of the simulation there are 50 000 possible estimates of the number of

equivalent service pipe bursts and these are ranked into a format that can be clearly

understood from a graph. The resulting graph not only indicates the most likely

number of equivalent service pipe bursts, but also the range in possible values.

The output from the sensitivity analysis is a distribution curve as shown in figure 4.3,

which indicates the probability of exceeding a particular number of equivalent service

pipe bursts. If the user wishes to alter any value in the table, this can be achieved by

selecting the particular number to be changed and typing over with a new value.

Figure 4.3 Example of sensitivity analysis (McKenzie, 2002)


50

The sensitivity analysis was repeated by changing the input values in the table. For

example, the lower estimate of the Average Zone Night Pressure (AZNP) can be

changed from 57.6 m (the default value of 72 – 20%) to 40 m and the upper estimate

changed from 86.4 m to 80.0 m.

CDLwin/PrimeLog - for programming, downloading and evaluating data (for instance,

flow rate and pressure) measured and recorded simultaneously using a Data Logger.

The pressure and flow rate relationship gives a detailed picture of the situation in the

pipeline. If, for example, the water pressure drops without the water meter registering

any flow, there is probably a leak up stream of the meter.

Water Demand Management Scorecard (WDM) (McKenzie, 1999) - for the

assessment of Water distribution systems to ascertain the Status quo of these systems

and evaluate the potential for Water Conservation / Water Demand Management

(WC/WDM) measures be implemented in these systems. The scorecard is to assess

the current situation regarding losses and levels of wastage in all water supply systems

by giving scores to the particular technical and managerial issues in the card. The

initiative provides the mechanism whereby the Water utility can identify areas where

WC/WDM is not being addressed properly to ensure that appropriate measures

are taken to encourage efficient use of water and the elimination of wastage. The

scorecard is based on a number of key issues which all water service providers must

address as part of normal management. Items in the Scorecard are inclusive of:

Development of Standard Water Balance – is there an existent water

balance for the utility that is frequently updated?

Effective Billing System- is the billing system and data management

system effective?

Network (leakage) complaints system-is there a leakage reporting and

data capturing system in place.


51

Billing and metering complaints system-is there a setup that allows

consumers to make complaints with regards to bills and meter reading

they query.

Asset Register for Water Reticulation system-is the network system

properly documented in terms of drawings and network information like

pipe size and length.

Asset management – are Capital, operations and maintenance works

efficient and effective.

Active leakage control-are leaks actively controlled or passive method is

employed.

Pressure management and maintenance of pressure reducing valves-

are pressure zones frequently managed as new developments come up

and are the existing PRV functional and properly maintained.

Regulations and bylaws-are these properly documented and distributed

to all interested parties.

Newspaper and radio articles plus posters and leaflets for distribution to

the public as an awareness method of the implication and consequences

of high levels of Non-revenue water.

4.8. WATER BALANCE


52

A water balance tracks every component of water that is delivered to and subtracted

from a supply system within a defined period of time. The standard format from IWA

(Table 4.1 below) was utilised to give the NRW and the steps are outlined below.

A B C D E

System Input

Volume

Authorized

Consumption

Billed

Authorized

Consumption

Billed Metered

Consumption

Revenue Water

Billed Unmetered

Consumption

Unbilled

Authorised

Consumption

Unbilled Metered

Consumption

Non-Revenue

Water(NRW)

Unbilled

Unmetered

Consumption

Water Losses

Apparent

Losses

Unauthorised

Consumption

Customer

Metering

Inaccuracies

Real Losses

Leakage on

Transmission

and/or

Distribution

Mains

Leakage and

overflows on

storage

facilities


53

A B C D E

Leakage on

service

connections

Table 4.2 The Water Balance standard format (IWA, 2003)

i. Entered System Input Volume Column A.

ii. Entered Billed Metered Consumption and Billed Unmetered Consumption in

Column D and enter total in Billed Authorised Consumption (Column C) and

Revenue Water (Column E)

iii. Calculated the volume of Non-Revenue Water (Column E) as System Input

Volume (Column A) minus Revenue Water (Column E)

iv. Determined Unbilled Metered Consumption and Unbilled Unmetered

Consumption in Column D then transfer total to Unbilled Authorised

Consumption in Column C

v. Added volumes of Billed Authorised Consumption and Unbilled Authorised

Consumption in Column C; enter sum as Authorised Consumption (top of

Column B)

vi. Calculated Water Losses(Column B) as the difference between System Input

Volume (Column A) and Authorised Consumption (Column B)

vii. Assessed components of Unauthorised Consumption and Metering

Inaccuracies (Column D) by best means available, add these and enter sum in

Apparent Losses(Column C)

viii. Calculated Real Losses(Column C) as Water Losses (Column B) minus

Apparent Losses(Column C)

ix. Assessed components of real losses (Column D) by best means available

(night flow analysis, burst frequency/flow rate/duration calculations, modelling),

add these and cross-check with volume of Real Losses in Column. C which

was derived from Step 8.


54

4.9. CALCULATION OF REAL LOSSES

The hydraulic equation for flow rate (L) through a hole of area A subject to pressure P

is;

L = Cd x A x (2gP) 0.5

Cd is a discharge coefficient and g is acceleration due to gravity. The effective area

(Cd x A) can be pressure-dependent for some types of individual leakage path. This

relationship uses the FAVAD (Fixed and Variable Area Discharge) concept and N1

exponent.

4.9.1. Leak Simulation

The method of real-time leak simulation utilised herein is based on the solution of

unsteady pipe flow by the Method of Characteristics (MOC) (Hayase et.al, 1995). The

general leak forms are:

1. Circumferential crack.

2. Loose weldment crack between two pipes.

3. Multiple small cracks

4. Longitudinal long crack

5. Loose union.

Leak is simulated by considering a flow diversion at the desired leak location as shown

in Figure 4.4. However, the leak must be considered at a computational section (NL).

Thus, the continuity equation at the leak location takes the following form:

QP1 − QP2 − qL = 0

Where Qp1 is the discharge just upstream of the leak location;

Qp2 is the discharge just downstream of the leak location and

qL is the leak flow rate.


55

Figure 4.4 Leak simulation by the Method of Characteristics (MOC) (Liemberger,

2007)

Due to the apparent analogy between a leak from pipe through-crack and an orifice

flow with respect to the head drop and flow rate relationship, the orifice equation is

used to compute the flow rate through leak and is given by:

𝑞𝐿 = 𝐶𝐿√𝐻𝐿

Where

qL is the leak rate;

CL is the dimensional leak opening coefficient; and

HL is the head at the leak location and is the head drop across the leak opening.

The drop in pressure along the pipeline HL was determined by measuring the upstream

pressure at the inlet valve or fire hydrant and the downstream pressure at a proxy

household.

The dimensional leak opening coefficient was determined from the graph shown in

Figure 5.3


56

Figure 4.5 Leak opening coefficient versus the square-root of the head loss

across the leak for the five leak cases (Liemberger, 2007)

4.9.2. Calculating Real Loss Performance Indicators

The new and most advanced real loss indicator (recommended by the IWA and the

AWWA) utilised is the Infrastructure Leakage Index (ILI). The ILI is a measure of how

well a distribution network is managed for the control of real losses, at the current

operating pressure. It is the ratio of Current Annual volume of Real Losses (CARL) to

Unavoidable Annual Real Losses (UARL).

ILI = CARL / UARL

Being a ratio, the ILI has no units and thus facilitates comparisons between countries

that use different measurement units (U.S., metric or imperial). But what are

unavoidable losses and how are they calculated? Leakage management practitioners

around the world are well aware that Real Losses will always exist - even in new and

well managed systems (Farley, 2008). It is just a question of how high these

unavoidable losses will be. The complex initial components of the UARL formula were

converted to a ‘user friendly’ pressure-dependent format for practical use (Farley,

2008):


57

UARL (litres/day) = (18 x Lm + 0.8 x NC + 25 x LP) x P

Where Lm = mains length (km);

NC = number of service connections;

LP = total length of private pipe, property boundary to customer meter (km);

P = average pressure (m).

CARL (litres/day)= Number of bursts x average flow rate x leak duration

The IWA water loss task force recommends the average flow rate as given in tables4.2

and 4.3below.

Reported Bursts Unreported Bursts

Location Flow rate l/hr./m pressure Flow rate l/hr./m pressure

Mains 240 120

Service Connection 32 32

Table 4.3 Flow rates for bursts

Location Flow rate l/km/d/m pressure

Mains 9.6

Service Connection 16

Table 4.4 Flow rates for background losses


58

The ILI is then interpreted according to the World Bank Institute banding system as

shown in the different categories in table 4.5 below

CATEGORY ILI RANGE DESCRIPTION

Developed

Countries

Developing

Countries

A <2 <4 Further loss reduction is uneconomic (unless

shortages); careful analysis needed to find effective

leakage

management

B 2 to 4 4 to 8 Potential for further improvement; consider pressure

management, active leakage control or maintenance

C 4 to 8 8 to 16 Poor leakage management, only OK if resource is

plentiful; even then, analyse leakages, intensify

reduction efforts

D >8 >16 Very inefficient use of resources, indicative of poor

maintenance and system condition in general, leakage

reduction programmes imperative (high priority)

Table 4.5 ILI interpretation banding system (World Bank, 2004)

The infrastructure leakage index

Is a non-dimensional performance indicator.

Measures how well the leakage management strategy of a water utility is

implemented.

Indicates the potential for further reduction of real losses.

Allows overall infrastructure management performance to be assessed

independently of the influence of current operating pressure.

Allows for comparison of different systems.


59

4.10. Data analysis and Strategy implementation

Analysis of the collected data was done; this involved the obtaining of the amount of

Non-Revenue Water through the water balance formation and losses calculation.

Strategies were then implemented over a period of 60 days so as to ascertain their

effectiveness as water demand management strategies. The strategies were run

concurrently.

The variation of real losses with time with respect to the action done to asset

management is shown in Figure 4.6 below. The various conditions from (a) to (d) show

how the real loss varies if there is no maintenance to the assets like pipelines and

valves up to condition oriented maintenance. This therefore instigated the need to

apply various strategies so as to reduce the NRW.

Figure

4.6 (a).

(b)


60

Figure 4.6 (c) and (d) variation of real loss with type of maintenance strategy

(Farley, 2008)


61

Generally there are four strategies that have proved effective in real loss reduction

and these are as shown in figure 4.7.

Unavoidable

Annual Real

Losses

Potentially Recoverable Losses

Speed and Quality of

repairs

Pip

elin

e a

nd

Asse

t

MA

na

ge

me

nt

Pre

ssu

re

Ma

na

ge

me

nt

Active Leakage

Control

Economic Level

of Real loss

Figure 4.7 Real loss reduction strategies (McKenzie, 2002)

1.Pressure management- this is the practice of managing system pressures to the

optimum levels of service ensuring sufficient and efficient supply to legitimate uses

and consumers, while reducing unnecessary excess pressures, eliminating transients

and faulty level controls all of which cause the distribution system to leak

unnecessarily.


62

A compromise however has to be reached so that there may be sufficient pressure to

the furthest and highest point consumer and not much pressure to increase the force

on the pipes which results in bursts.

3. Active leakage control, speed and quality of leak repairs- this articulates the

need for increase in awareness, location and repair time for the leaks. The

passive method relies on reported leaks and this may take longer.

3. Pipeline and Asset management-this involve the selection and installation of the

correct material in a correct manner. The maintenance of the assets is also vital as the

constant monitoring that leads to the decision of whether to replace the assets or repair

the existing ones.

The only strategies that were used are:

1. Step testing, where the District Metered Area (DMA) was sub-divided

into smaller areas by systematic closing of valves usually during the

minimum night flow. The flow data was analysed to see the variation of

consumption with pressure and areas suspected to have leakage are

identified to be followed up by leak location (IWA 2003). Step tests have

the following advantages (Farley and 2003):

Results are immediate; and

Leak location can be done immediately.

2. Active leak detection

3. Apparent loss reduction by


63

4.11. Summary of methodology:

1. Determination of the System Input Volume (SIV) into Cowdray Park at the

existing District Meter that also has a PRV installed.SIVis the volume of water

input to a transmission system or a distribution system.

2. Formulation of the Water Balance for Cowdray Park by use of the standard

format recommended by IWA.

3. Determination of the real and apparent losses. Real losses can be severe, and

may go undetected for months or even years (IWA, 2003). The volume lost

depends largely on the characteristics of the pipe network and the leak

detection and repair policy practised by the organisation (Lambert and May,

1994), that is;

• The pressure in the network

• The frequency and typical flow rates of new leaks and bursts

• The proportions of new leaks which are ‘reported’

• The "awareness" time (how quickly the loss is noticed)

• The “location” time (how quickly each new leak is located)

• The repair time (how quickly it is repaired or shut off)

• The level of “background” leakage (undetectable small leaks)

4. Calculation of the Non-Revenue water.

5. Formulation of reduction strategies according to the losses experienced, for

instance:

6. Application of strategies for two months so as to assess the efficiency and

effectiveness of the strategies.

7. Checking of NRW reduction using performance indicators namely the

Infrastructural Leakage Index (ILI) and financial Indicator (IWA, 2003).


64

The general form of the methodology summary adopted is articulated by the flow chart

shown in Figure 4.8 below

DETERMINATION

OF SIV

DETERMINATION

OF BILLED

PROPERTIES

Use of data

loggers

Data from

Billing section

CALCULATION OF NON-

REVENUE WATER

Use of water

balance

FORMULATE AND APPLY

REDUCTION STRATEGIES FOR

2 MONTHS

ASCERTAIN REDUCTION IN NRW

LEVELS

Use of perfomance

indicators

Figure 4.8 Methodology Flow Chart


65

5. RESULTS AND DISCUSSION

5.1. INTRODUCTION

This chapter serves to achieve the overall objective to this research project. It lays the

analysis for calculating the Non-Revenue water through the water balance and the

various losses involved

The total number of water consumers (subscribers) is 7 553 (Billing data, Appendix

D). Considering an average household size of 4.5 this is equivalent to approximately

34 000 recorded consumers in the City of Bulawayo billing database.

5.2. Data logging

The area was logged and the results downloaded and exported to excel format as in

Annexure C to give the various consumption and pressure patterns. The logging

proved that the consumption is low at night and pressure is consequently high. The

consumption and pressure pattern over the logging period is shown in Figure 5.1, this

depicts that the consumption is low during the period from midnight to about

04.00hours when people wake up. During this period there is a pressure build up in

the pipes as there is no point of exit for the water, pressure increase to a maximum of

65m. This indicates that there is an inverse relationship between pressure and

consumption.


66

Figure 5.1 Consumption and pressure versus time graph measured at the

District meter

Where series 2 is the consumption and series 5 is the pressure.

Certain Households were logged so as to obtain the pressure distribution that would

lead to a decision whether pressure management strategies are required or not. An

instance of the pressure pattern is shown in Figure 5.2 in which the pressure builds up

at night and reduces during peak periods. Most of the real losses are experienced at

night when pressure is high this is due to weak pipes not being able to withstand the

pressure increase. The negative pressures recorded imply that a vacuum was created

in the pipeline due to a bursts somewhere along the line leading to water not getting

to other places and suction created due to differences in the pressure gradient

between the pipeline and the surrounding atmosphere.

-10

0

10

20

30

40

50

60

70

0

10

20

30

40

50

60

Pre

ssu

re (

m)

Co

nsu

mp

tio

n (

m3

/hr)

Time

Consumption and Pressure vs time graph

Series2

Series5


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Figure 5.2 Pressure patterns at households

5.3. System input volume (SIV)

During the logging period of 48 hours at the pressure reducing valve (PRV) a total of

15 409 m³ were delivered into the pilot area. This volume translates to an average

water volume of 7 704.5 m³/day.

This system input / water demand in the service area is mainly consumed by

subscribers who in turn pay the Water Utility for the service. This quantity of water is

generally referred to as Revenue Water (RW) because it generates income. A large

quantity however is lost and must be considered as Non-Revenue-Water (NRW).

Effectively the Water Utility is losing money with every cubic meter.

-1

0

1

2

3

4

5

Pre

ssu

re (

bar

s)

Time

Pressure vs time graph

P4


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5.4. Apparent losses

Two undesired types of water consumption are generally described as apparent

losses:

(a) Unauthorized Consumption (or illegal connections) which would be for example a

consumer that benefits from his subscribed neighbour. The customer survey

conducted recently revealed that approximately 10% of the dwellings are not

registered subscribers. Assuming that illegal water users consume the same

amount of water as subscribed customers, results in a daily water loss of

770.45m³/day.

(b) Metering inaccuracies exist with every kind of water meter. Under-reading

volumes (when low flow is not captured) and actual inaccuracies (when the

meter is old and worn) are the main components. Since the water meters in

Cowdray Park are comparatively new a value of 5% of the metered

consumption was reasonably considered, which corresponds with

385.23m³/day.

The bulk water meter was reading uncharacteristic flows or not recording at all

in some instances. The water meter was recently installed by the City of

Bulawayo but intermittent water supplies does lead to meter reading errors.

Success in reduction of non-revenue water can be measured and monitored

with proper flow measurement from both bulk water supply and billing.

5.5. Real losses

Total consumption during the logging period was 7 704.5 m3/d. The minimum night

flow, was recorded at 4.2 ℓ/s (which is 15m3/hr. read of from the graph). Adjusted for

legal night consumption which assumes that 6% of the population is active at night

and utilises 100l/day (Farley, 2008) the leakage in the area at night is 4.2 ℓ/s – 2.4 ℓ/s

= 1.8 ℓ/s.

The net night flow can be converted into a daily leakage of 155.52m3/day.

From the door to door survey, it was found that the average waste at the private

premises to be 8.0 ℓ/day.connection, thus losses in the distribution system was

calculated to be 66.9m3/day for Cowdray Park.


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The volume of leakage can otherwise be obtained from the Equation 5.1;

Volume of leakage (litres/day) = Number of bursts x average flow rate x leak duration

…Equation 5.1

Number of bursts and leak duration were found from the BCC records as 3 per day

and 3 days respectively, with an average pressure of 45m. The average flow rate is

obtained from the orifice equation or the International Water Association flow rate

recommended tables (IWA, 2003)

Therefore:

Volume of leakage (litres/day) = 3/day x 240 ℓ/hr.m pressure x 72 hrs.

= 2 332800ℓ/day = 2 332.8m3/day

Field measured pressure revealed that the installed PRVs are not regulating the

pressures as expected. It is noted that if the PRVs are not working properly, this may

subject the network to pressure spikes leading to pipe bursts

5.5. House meters

Some house meters in the pilot and control areas were randomly tested using a

portable test meter. Results from these tests are summarised in Table 5.1.

Parameter Value

Number of meters 7553

Tested meters 380

Faulty meters * 74

Discrepancy incl. faulty meters -5.1 %

Discrepancy exc. faulty meters -0.3 %

Average age (year) 7

Table 5.1 Test house meters

* House meter yields 25 % to 100 % lower or higher value than the test meter


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It was estimated that 30 % of all connections do not have a meter, which corresponds

to Councils own records. All connections with missing or stopped meters are billed

based on an estimated average consumption, hence the consumption figures from the

billing system should be a reasonable estimate of the actual total consumption.

It can be concluded that house meters generally are in good condition with an under-

reading of approximately –1.0 % based on the different monthly readings from

Bulawayo City Council. Faulty meters amounts to approximately 19.5 % of all meters.


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5.6. Water Balance

The water balance for the Cowdray Park area was determined utilising the value

recorded on the field and those calculated. The SIV was measured on the field, the

real and apparent losses were obtained by a combination field measurements,

documented data from City of Bulawayo and calculations. Figure 5.2 summarises the

water balance and its various components.

System Input

Volume

7 704.5m3/day

Authorized

Consumption

4216.02m3/day

Billed Authorized

Consumption

3 842.73m3/day

Billed Metered

Consumption

3 842.73m3/day

Revenue

Water

3 842.73m3/day

Billed Unmetered

Consumption

0m³/day

Unbilled

Authorised

Consumption

373.29m³/day

Unbilled Metered

Consumption

373.29m³/day

Non-Revenue

Water(NRW)

3 861.77m3/day

Unbilled Unmetered

Consumption

0m³/day

Water Losses

3488.48m3/day

Apparent Losses

1155.68m³/day

Unauthorised

Consumption

770.45m³/day

Customer Metering

Inaccuracies

385.23m³/day

Real Losses

2 332.8m3/day

Leakage on

Transmission and/or

Distribution Mains

2 332.8m3/day

Leakage and overflows

on storage

facilities

Leakage on service

connections

Table 5.2 Cowdray Park water balance in standard IWA format (IWA, 2003)


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5.7. Strategies Implemented

Visual pipeline survey detected 90 % of the leaks, but sounding proved to be

an effective method of detecting underground leaks. It was noted during the

field investigations, that some of the valve chambers were full of water from

leaking valves and some of the fire hydrants were found leaking.

Cutting off illegal connections realised 70% of the revenue with not much

change in water quantity as the consumers would formalise their connections

in not more than 2 weeks.

5.8. Infrastructural leakage index (ILI)

ILI = CARL / UARL

UARL (litres/day) = (18 x Lm + 0.8 x NC + 25 x LP) x P

Where Lm = mains length (km) = 38.5km

NC = number of service connections = 8 566

LP = total length of private pipe, property boundary to customer meter (km) = 109.3km

P = average pressure (m) = 45m

UARL (litres/day) = (18 x 38.5+ 0.8 x 8566 + 25 x 109.3) x 45

= 462 523.5 l/day = 462.5m3/day

CARL (litres/day) = Number of bursts x average flow rate x leak duration

Volume of leakage (litres/day) = 3/day x 240 l/hr.m pressure x 72 hrs.

= 2 332 800 l/day = 2 332.8m3/day


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ILI = 𝟐 𝟑𝟑𝟐. 𝟖𝟒𝟔𝟐. 𝟓⁄ = 𝟓. 𝟎𝟒

The ILI value of 5.04 hence according to the ILI interpretation banding system (Table

5.3) there exists potential for further improvement of loss reduction, pressure

management systems should be considered and adopt active leakage control or

maintenance.

There always exists the potential to further reduce the NRW value and this would allow

the Water Utility of Bulawayo saving considerable costs (including energy required for

pumping and chlorine for disinfection). Therefore NRW should be reduced to the

greatest possible extend and values of 10% to 15% may be considered as a maximum

if water is abundant and cheap. Levels below 10% should be envisaged if water

requires a lot of pumping and treatment. However, a better understanding of the

composition of NRW in the service area is required in order to define measures for

reducing NRW.

The Key differences before and after implementing various strategies are summarised

in table 6.2

Parameter Before strategy After Strategy Reduction

S.I.V 7 704.5m3/day 7 704.5m3/day nil

Number of bursts 3/day 3/day nil

Leak duration 72 hrs. 48hrs. 33%

Real Losses 2 332.8m3/day 1 555.2m3/day 33%

Apparent Losses 1528.97m3/day 1443.88m3/day 5%

NRW 3 861.77 m³/day 2 999.08 m³/day 10%

ILI 5.04 1.68 67%

Table 5.4 Difference before and after implementation of strategies.


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6. CONCLUSIONS AND RECOMMENDATIONS

6.1. Introduction

From the analysis and results in chapter five Non-Revenue Water reduction can be

used as water demand management tool this is evident by the amount of water and

revenue saved through implementing just a few strategies, this goes on to represent

that if all strategies are applied and resources directed to Non-Revenue water

reduction then the City can save water and realise revenue. With regards to the

objectives the conclusions are:

6. To quantify the system input volume (SIV) – the SIV was obtained by use of

data logging at the Bulk Meter and was found to be 7 704.5m3/day

7. To quantify the amount of Non-Revenue Water (NRW) – billing data base was

obtained from the billing section and about 7 553 properties were billed to give

the revenue water, the remainder is the Non-Revenue water. Amount was

obtained to be 3 861.77 m³/day and 2 999.08 m³/day before and after

implementation of strategies respectively.

8. To construct a water balance for the Cowdray Park Network- a standard IWA

water balance was constructed using Aqualite, with inputs measured and

some calculated.

9. To quantify amount of real and apparent losses in the network- calculation

were done after field measurements to determine losses and these were

inputs into the water balance

10. To establish location of highest losses in the system – Minimum night flow

analysis and visual leak inspection in conjunction with step testing revealed

the weak points were bursts were frequent and at high rates.

11. To formulate maintenance strategies or plans of the existing network- relevant

strategies were formulated and applied over two months to tests their

efficiency and effectiveness.


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6.2. Non-revenue water

The most important result for the service area of Cowdray Park is the Non-

Revenue-Water (NRW). In order to obtain the volume of NRW the following

formula was adopted:

Non-Revenue Water (NRW) = System Input – Revenue Water

Considering that the Water Demand (System Input) is 7 704.5 m³/day and that

only 3 842.73 m³/day are consumed (and paid) by subscribers (Revenue Water)

the balance of 3861.77 m³/day is Non-Revenue Water. Based on this, about 50%

of the System Input water was initially lost as Non-Revenue Water in Cowdray

Park this amount was then reduced to 2 999.08m³/day after implementing the

strategies for a period of two months, which is about 40% of the SIV. This is after

using the same calculations as before implementation, by use of the re-measured

data and City of Bulawayo data in Annexure A.

6.3. Projections of losses

The results clearly identified losses on the distribution system as the main

contributor of Non-revenue Water as it contributes 2 332.8m3/day (66.9%). The

losses were found using the minimum night flow (MNF) method and real loss

calculation using volume of leakage (equation 5.1), after allowing for installation

losses at the private premises as these losses/waste are billed through the billing

system and accepted as background leakage (dripping taps etc.).

6.4. Findings

This study of Cowdray Park area, concluded that:.

Losses take place in the distribution system (Leaking valves, hydrants and burst

mains).

In general it seems feasible to reduce losses down to 100 ℓ/h (2.4m3/day). with

introduction of active leakage control.


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Leak detection: Visual inspection detected most leaks and step-testing proved to

be difficult as most of the valves were buried and had not been regularly

serviced.

Pressure was not stable during the period of measurements, and caused

frequent burst pipes and other leaking spots as valves and hydrants. The

unstable pressure was due to PRV’s not working properly and to incorrect

closure and opening of valves. As an overall finding this emphasis the need of

better pressure control and improved maintenance and operation of valves.

Due to the responsible attitude to water rationing adopted by most residents,

waste is not considered to be a major problem. The household survey

confirmed this to be the case with losses at the household level estimated to be

8.0 ℓ/h (0.19m3/day) and connection.

Utility maps were not up-dated, and reduced the effectiveness of visual

inspection. The exercise showed the need for up-dated maps, to be able to find

leaks for both visual inspection and sounding.

House meters were generally in good condition and those in operation were

under-reading by 1.0 %. However, the study showed that approximate 8 % of

existing meter should be replaced as they are malfunctioning or inaccurate.

These connections were billed uniformly according to average consumption in

the actual area.

6.5. RECOMMENDATIONS

6.5.1. Asset Management

Significant gains in the non-revenue water reduction can be achieved at Cowdray Park

by focusing on asset management. All assets require management of some kind to

ensure optimal performance. Asset management is a key strategy in reducing non-

revenue water as the scope covers the entire water supply cycle from abstraction right

through to water billing and collections.


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Pipeline Assets - The pipeline network comprises pipelines made of AC/PVC

pipe materials. Some of these pipelines are close to or have exceeded their

design life and should be considered for rehabilitation or replacement. It is not

recommend that pipelines be replaced simply based on the remaining useful

life criteria (Liemberger, 2010). Experience elsewhere has shown that

pipelines can continue to perform well beyond the design life depending on

the soil conditions the pipe is laid in, the network operation pressure and to

some extent the quality of the water conveyed (Liemberger, 2010)). At this

stage, it is recommended that the identification of the pipelines due for

replacement, be based on the operational conditions of the pipelineand the

pipe burst history of the pipelines. The operational conditions have been

established from the hydraulic model and the experience of the system

operators (institutional knowledge). The specific pipelines operating under

high pressures have been identified. This is consistent with the report on pipe

bursts history provided by the operations team. It is recommended that certain

pipelines be replaced in these areas as well.

Valves and Fire hydrants–these are included in the asset management and

should be serviced or renewed according to their functionality or lack of it

thereof. A fair amount of water can be lost through leaks from valves and fire

hydrants.

Pressure Reducing Valves -. It is recommended that the condition of all the

PRV be ascertained and if not functioning properly be serviced or replaced.

Bulk Water Meters and Consumption Meters – It is recommended that bulk

water meter be assessed and serviced accordingly. Additionally it is

recommended that new consumer meters be installed, to facilitate accurate

billing for water used. It is further recommended that a programme to align the

billing zones with the DMA be initiated so that an accurate water balance can

be produced.


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6.5.2. Pressure Management

The rate of leakage in water network is proportional to the network operating pressure.

Additionally, the frequency of pipe bursts is also related to the network operating

pressure. Pressure management is therefore a crucial step in non-revenue water

reduction. Operating pressure reduction has the added advantage of increasing the

useful life of the network.

There is a physical relationship between leakage flow rate and pressure (Figure 6.1),

and the frequency of new bursts is also a function of pressure:

The higher or lower the pressure, the higher or lower the leakage.

The relationship is complex, but utility managers should initially assume a

linear relationship (10% less pressure = 10% less leakage)

Pressure level and pressure cycling strongly influence burst frequency.

Figure 6.1 Pressure/ leakage relationship (Farley and Trow, 2003)

It is therefore strongly recommended that the pressure reducing valves that have

been installed be maintained in a serviceable state all the time to maintain the status

already achieved. If the pressure reducing valves are not properly maintained and


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the network is exposed to random pressure spikes, the deterioration rate for the

network will be accelerated.

6.5.3. Active Leak Detection

Active leak detection is a long term strategy for reducing non-revenue water. This

programme was implemented at Cowdray Park during the project duration albeit with

limited resources. It is proposed that this programme be continued but it is envisaged

that immediate results can be realised by use of leak detection in conjunction with

other strategies like wide spread cutting off illegal consumers and pressure

management strategies.

6.5.4. Efficiency in effecting Repairs

The speed at which a leak is repaired after being detected is crucial. The longer it

takes to repair the leak the more water is lost. The volume of water lost increases as

the awareness, location and repair time increase as shown in Figure 6.2.

Figure 6.2 The effect of time on the total volume lost (Farley and Trow, 2003)

Additionally, the workmanship during the repair process will determine whether the

repair can be sustained or not. Good workmanship can be achieved by training of


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the staff operating the network. This considered as a long term objective and may

not result in immediate measurable gains or reduction in non-revenue water.

6.5.5. Capacity building

Successful implementation of the non-revenue water reduction strategies requires a

collective effort from the management and staff from all the departments at the City of

Bulawayo key being the Engineering services and the City Treasurer’s Departments.

Capacity building of Council staff should therefore been targeted at all these levels in

the form of training workshops, on the job training to operations staff and network

hydraulic modelling development.

Resources should also be directed towards monitoring and maintenance of the assets

such as pipeline, valves and meters. This will work towards promoting the Virtuous

cycle. Procurement of new and efficient meters is necessary together with data loggers

to frequently monitor flow and pressure patterns in the system.

6.5.6. Significance of the study

The reduction of Non-Revenue Water in this study has proved that Non-Revenue

water reduction can be applied as a water demand management tool. The universal

slogan of survey states “working from the known to the unknown” and in this instance

the NRW levels were obtained and application of recommended strategies will assist

the water utility to focus on water conservation and realization of revenue at grass

roots.

The 3 861.77 m³/day Non Revenue water translates to a minimum of $3 861.77 lost

per day by the water utility and realisation of this revenue by adopting reduction of

NRW can assist in mobilisation of resources by transforming the Vicious NRW cycle

to the Virtuous cycle.


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APPENDICES

Reduction of Non-Revenue water as a water demand management strategy(Case Study)

Documents

Transcript of Reduction of Non-Revenue water as a water demand management strategy(Case Study)