Physics and Chemistry of the Earth 28 (2003) 805–815

www.elsevier.com/locate/pce

Analysing water use patterns for demand management: the case ofthe city of Masvingo, Zimbabwe

Emmanuel Dube a,*, Pieter van der Zaag b,1

a Municipality of Masvingo, P.O. Box 17, Masvingo, Zimbabweb Department of Civil Engineering, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe

Abstract

Water use in urban centres is dynamic, fluctuates, differs between high and low-income users, and tends to increase over time.

Supply infrastructure can often hardly keep pace with increased water consumption. Given (a) the high cost of infrastructure de-

velopment, (b) the recent emphasis on demand management, and (c) the social obligation to provide water services to the poor,

urban water providers are faced with an important choice: whether to go the demand management route, or to continue con-

structing new infrastructure. This paper sheds light on some of the possibilities and constraints of both choices by providing a case

study of the city of Masvingo in Zimbabwe. The paper analyses water use patterns in this city with a population of 70,000, located in

a drought prone region of average rainfall of 600 mm/a. Water consumption has reached the limits of the water supply capacity. The

paper first looks at the long-term water use pattern of the city as a whole and the factors that have caused the observed pattern using

multiple linear regression. The paper then analyses the patterns of water use of rich and poor households, and attempts to assess the

(im)possibilities of influencing these by means of an appropriate tariff structure. In projecting future demand, the paper then

considers a number of interventions that could influence demand, which include leakage control, pressure management, awareness

campaigns, free technical advice to water users, as well as a new tariff structure. It also discusses when new supply infrastructure

should be available, depending on the various demand management measures taken.

� 2003 Elsevier Ltd. All rights reserved.

Keywords: Demand management; Elasticity of demand; Supply management; Unaccounted-for water; Water loss; Water use projection

1. Introduction

Demand management aims at achieving desirable

demands and desirable uses. It influences demand in

order to use a scarce resource efficiently and sustainably.

This definition implies that water demand management

may also include measures aimed at stimulating water

demand in sectors where current use is considered un-

desirably low. Apart from structural measures (such as

installing low-flush cisterns for toilets, leak detectionand control systems in distribution networks, and drip

irrigation in agriculture), demand management strate-

gies mainly consist of non-structural measures: eco-

nomic and legal incentives to change the behaviour of

water users; and the creation of the institutional and

policy environment that enables this approach (Savenije

*Corresponding author. Fax: +263-39-62257.

E-mail addresses: timire2000@yahoo.co.uk (E. Dube), zaag@eng.

uz.ac.zw (P. van der Zaag).1 Fax: +263-4-336725.

1474-7065/$ - see front matter � 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/j.pce.2003.08.004

and Van der Zaag, 2002). The concept of demand

management is widely gaining recognition but its effec-tiveness in practice depends on the political will to im-

plement the available possible least cost measures. In

many water using sectors there is scope for water de-

mand management. This paper focuses on urban water

supply in a town that faces water scarcity.

Water use in urban centres is dynamic, fluctuates and

differs between high and low-income users and tends to

increase over time. For most urban centres water supplyand demand form among other factors, the backbone

for urban development and growth. Given the high cost

of new infrastructure development, the recent emphasis

on demand management and the social obligation to

provide water services to the urban poor, water pro-

viders are faced with an important choice: whether to go

the demand management route or to proceed with new

infrastructure development. This paper, which is basedon Dube (2002), looks at the situation in the city of

Masvingo in Zimbabwe where the local authority has

found itself in this dilemma.

Fig. 1. Map of Zimbabwe with the city of Masvingo.

806 E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815

The city of Masvingo lies approximately 300 km to

the south of Harare, Zimbabwe’s capital city (Fig. 1). It

is situated in a drought prone area, with average rainfall

of 600 mm/a. The city’s population is estimated to be

70,000 people in 2002. The raw water source for the city

is Lake Mutirikwi. Apart from providing water for the

2.000

3.000

4.000

5.000

6.000

7.000

8.000

1977 1979 1981 1983 1985 1987 19

trea

ted

wat

er p

rodu

ced

(1.0

00 m

3/a)

Fig. 2. Production of treated water,

0

5.000

10.000

15.000

20.000

25.000

30.000

35.000

1977 1979 1981 1983 1985 1987 1

trea

ted

wat

er (m

3/da

y)

plant capacityaverage treated water pumped

Fig. 3. Pattern of water supply for th

city of Masvingo, Lake Mutirikwi supports water sup-

ply schemes for several riparian farmers and large sugar

cane irrigation schemes in the Triangle and Hippo

Valley areas. The storage capacity of the lake, which was

completed in 1960, is 1.4 · 109 m3 and is a reliable source

of water to the city. Water use in Masvingo has in-

creased through the years, from 2.4 Mm3/a in 1977 to6.8 Mm3/a in 2001 (Fig. 2).

The water works were upgraded in 1982 to their

current capacity of producing 24,000 m3/day of treated

water. This is no longer sufficient to meet the demand

during the hot dry months of September and October,

when the water supply system may produce 28,000 m3/

day under severely stressed conditions (Fig. 3).

This paper first describes past trends in water use(Section 2), and quantifies the influencing factors (Sec-

tion 3). It then describes domestic water use by affluent

and non-affluent households (Section 4), and critically

assesses the current tariff for domestic water, while

proposing an alternative tariff structure (Section 5). The

paper then projects future water demand, taking various

water demand management measures into account

(Section 6). The paper concludes with a combination ofmeasures that tackle both the demand and the supply

side, in order to stave off Masvingo’s looming water

crisis.

89 1991 1993 1995 1997 1999 2001

city of Masvingo, 1977–2001.

989 1991 1993 1995 1997 1999 2001

peak day water pumpedaverage peak week water pumped

e city of Masvingo 1977–2000.

Table 1

Treated water produced and water use, Masvingo, 1991–2001

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Treated water produced

(Mm3/year)

6.06 5.96 4.85 4.88 5.43 5.74 5.68 6.59 6.26 6.19 6.78

Billed total (Mm3/year) 5.88 5.84 3.21 4.23 4.47 5.29 5.33 5.69 4.96 5.44 5.86

Non-billed water (%) 2.9 2.0 33.8 13.3 17.7 7.8 6.2 13.7 20.7 12.1 13.6

Billed domestic (Mm3/year) 3.29 3.42 2.31 3.02 3.02 3.19 3.82 3.97 4.11 4.29 4.73

Billed industry (Mm3/year) 2.59 2.42 0.90 1.21 1.45 2.11 1.51 1.73 0.85 1.15 1.13

Population (1000) 49.6 51.7 53.9 56.0 58.1 60.2 62.3 64.4 66.6 68.7 70.8

Treated per capita (lcd) 335 316 246 239 256 261 250 281 257 247 262

Table 2

Unaccounted-for water in Masvingo (Dube, 2002)

Source Amount (m3/day)

Unavoidable background losses 700

Leakage in distribution mains 1300

Pipe bursts 500

Cooden Reservoir leakage 100

Total unaccounted-for 2600

E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815 807

2. Trends in water use

Water use in the domestic sector has increased with

time whereas in the industrial and commercial sector it

has decreased (Table 1). Water consumption in the in-

dustrial sector is not likely to grow as Masvingo’s two

major water users have either closed down (United

Bottlers) or scaled down operations (Cold Storage

Company).Water use is influenced by the occurrence of severe

droughts, when demand is suppressed through intensive

water campaigns, rationing measures and decreased

economic activity. Fig. 2 shows a decrease in water use

during the two major droughts of the past 25 years

(1983/1984 and 1992/1993). After both droughts water

use picked up again, albeit at different (decreasing) rates:

• Over the period 1977–1983 water use increased at an

average rate of 8% per annum;

• Due to the drought of 1983–1984, water use de-

creased from 4.5 to 3.7 Mm3/a;

• From 1985 to 1993 water use increased again at an

average rate of 5% per annum;

• The drought of 1992 saw a decrease in water use from

6.0 to 4.8 Mm3/a;• Since 1993 water use increased again at an average

rate of 3% per annum.

The crude per capita water use (total treated water

divided by the population) in the city of Masvingo has

decreased from 380 litres per capita per day (lcd) in 1979

to 260 lcd in 2001 (Table 1). The billed domestic water

use stood at 180 lcd in 1991; dropped immediately afterthe drought of 1992 to 120 lcd; and in 2001 reached the

level of 1991.

Data on unaccounted-for water (non-billed fraction

of treated water produced) fluctuate widely and appear

inconsistent (Table 1). Detailed research over the period

1999–2001, however, shows a fairly consistent picture of

15% unaccounted-for water (2600 m3/day; 0.95 Mm3/a),

which is considered reasonable though not beyond im-provement. Dube (2002) conducted leakage surveys,

measurements of minimum night flows, and reconciled

water delivered at certain sectors with measured

household consumption. Though the data were not al-ways consistent, he estimated the sources of water losses

(Table 2).

3. Quantifying the factors influencing water use

In order to better understand the factors influencing

water consumption, a multiple linear regression (MLR)analysis was carried out, taking into account the fol-

lowing factors (Singh, 1999; DfID, 2001): population,

rainfall, economic development and rationing.

Annual data for population and rainfall were avail-

able for Masvingo. For economic development, national

data for GDP growth were used as a proxy. For ra-

tioning, a dummy factor was used with a memory of 5

years, which decreases from 1 to 0 in steps of 0.2 peryear. Appendix A provides the data used for the MLR

analysis, as well as the output. The data show that while

the urban population has increased steadily over the

past 20 years, GDP at national level has been fluctuat-

ing. For the drought years of 1983/1984 and 1992/1993

per capita GDP was negative at )4.2% and )4.8% re-

spectively.

For the MLR, the following formula was used:

Q ¼ aþ b� N þ c� P þ d � Gþ e� R ð1Þ

where Q¼ annual treated water pumped (1000 m3/a);N ¼ population of Masvingo (1000); P ¼ annual precip-

itation (mm/a); G¼GDP growth (%); R¼ factor for

rationing, with a memory of 5 years (decreasing from 1

to 0 in 6 years); a, b, c, d and e are constants.

808 E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815

The MLR analysis yielded the following values for

the constants a, b, c, d and e :

Q ¼ 1496þ 90:2� N � 1:5� P þ 26:8� G� 837� R

r2 ¼ 96:5 ð2Þ

Formula (2) implies that:

• Constant a (1496 · 103 m3/a) represents water uses

that are more or less fixed and independent of popu-

lation, rainfall, GDP and rationing. These uses in-

clude water losses (950 · 103 m3/a, see above), to

some extent institutional water uses, and to a lesserextent industrial and commercial uses.

• Constant b (90.2 m3/capita/a, equivalent to 247 lcd)

represents the ‘‘crude’’ per capita water consump-

tion, and includes some industrial and commercial

uses. Population alone explains 88% of total water

supply.

• Constant c (1.5 · 103 m3/mm) means that if rainfall is

100 mm above the average of 600 mm/a, water con-sumption decreases with 150,000 m3/a; if rainfall is

100 mm below average, consumption increases with

the same amount. Including rainfall improves the

correlation with 5%.

• Constant d (26.8 · 103 m3/a) implies that change in

GDP has relatively little effect on water consumption:

a 1% increase in GDP leads to an increase in water

consumption of 27,000 m3/a. Including this factor in-creases correlation with only 0.4%.

• Constant e (837 · 103 m3/a) indicates that ration-

ing has a significant impact on water consump-

tion: in a drought year consumption drops by

837,000 m3/a. Including this factor improved cor-

relation with 3%, yielding a total correlation of

96.5%.

The multiple linear regression analysis gave a good fit

(Fig. 4). Future water use can be projected based on past

water use and various scenarios can be considered which

take into account the factors that influence water use

(see Section 6, below).

2.000

2.500

3.000

3.500

4.000

4.500

5.000

5.500

6.000

6.500

7.000

1977 1979 1981 1983 1985 1987 1

trea

ted

wat

er (1

.000

m3/

a)

MLR model

observed

Fig. 4. Observed and modelled wat

4. Water use by affluent and non-affluent households

Trends in domestic water use were further studied

by considering affluent and non-affluent residential ar-

eas. The residential areas of Rhodene and Clipsham were

considered affluent, comprising a sample of 1050 house-

holds. The residential areas of Rujeko and Muchekewere considered non-affluent, represented by a sample

size of 3350 households. The total sample size represents

some 34% of all domestic users of Masvingo. Monthly

water consumption was derived from billing data of

1999–2001. The results of average consumption patterns

in different residential areas are presented graphically in

Fig. 5.

Fig. 5 shows that there is a large difference in waterconsumption between affluent (consuming 59 m3/month

on average) and non-affluent households (20 m3/month).

Moreover, water consumption fluctuates much more in

affluent households (coefficient of variation CV of 31%)

than that of non-affluent households (CV¼ 11.5%). This

fluctuation is related to rainfall, as water use tends to be

higher in the hot dry months, especially for non-essential

purposes such as the use of treated water for wateringgardens. In the hot dry month of October, for instance,

affluent households may consume as much as 80 m3/

month or more, whereas their non-affluent counter-

parts consume at most 25 m3/month, i.e. less than a

third. In the poorest section of the city (500 house-

holds within Mucheke residential area) average house-

hold consumption was only 12 m3/month. This amount

may therefore be considered the basic minimum or‘‘lifeline’’ amount, and is, with an average household

size of eight persons, equivalent to 50 lcd (cf. Gleick,

1996, 1999).

The explanation for the observed trend is clear: poor

households cannot afford to use a lot of water because of

their inability to pay. In addition, they have relatively

small plot sizes (200–300 m2) which puts an upper limit

to the use of water for gardening even if they did havethe ability to pay. As a result, the seasonal variation in

their water use is relatively small, since water is mainly

used for the most essential purposes. For the affluent

989 1991 1993 1995 1997 1999 2001

er use, Masvingo, 1977–2001.

0

10

20

30

40

50

60

70

80

90

100

Jan-99 A pr-99 Jul-99 Oct-99 Jan-00 Apr-00 Jul-00 Oct-00 Dec-00 Apr-01 Jul-01 Oct-01wat

er c

onsu

mpt

ion

(m3

per m

onth

per

con

nect

ion)

Rhodene+Clipsham

Rujeko+MuchekeRhodene+Clipsham: a v. 59.3 m3/month; c v = 31%; n=1050

Rujeko+Mucheke: av. 19.9 m3/month; c v = 11.5%; n=3350

Fig. 5. Monthly billed water consumption by affluent and non-affluent households, 1999–2001.

E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815 809

household the opposite is true: their ability and will-

ingness to pay is large, and water use is seemingly re-

stricted by the size of their gardens (4000 m2 on

average), the presence of a swimming pool as well as thenumber of cars they wish to wash. A large part of water

is thus applied to uses that are considered non-essential.

It may therefore be hypothesised that the CV of

monthly consumption data is an indicator for the elas-

ticity of demand. This hypothesis would suggest that the

elasticity of demand for water in affluent households in

Masvingo may be 2.7 times higher than that for poor

households (31/11.5¼ 2.7). Detailed economic researchwould be required to falsify or accept this hypothesis.

This preliminary finding suggests that water pricing in-

fluences water use by affluent households to a much

larger extent than that of non-affluent households.

5. Masvingos tariff structure

The city of Masvingo derives its largest income from

the water account, which contributed between 25% and

40% of council’s revenue since 1995 (Table 3). The City

Council made, on average, about 80% profit on each

cubic metre of water sold during 1999–2001. The water

account is able to meet the present operation and

maintenance needs of the water supply utility. If it had

Table 3

Revenue and expenditure from water, Municipality of Masvingo

Year Expenditure for water

supply (MZ$/a)

Revenue from

water (MZ$/a)

Net profit

water (MZ

1995 5.59 6.45 0.86

1996 7.57 8.30 0.73

1997 8.76 10.83 2.07

1998 16.43 23.20 6.77

1999 16.26 28.30 12.04

2000 25.44 45.50 20.06

2001a 44.11 80.60 36.49

aUn-audited figures for 2001.

been independently managed it would have had suffi-

cient funds for the provision of the now needed infra-

structure. The water account, however, is pooled with

the city’s general account and income from water isapparently used to subsidise council’s many other key

activities such as providing primary health care and

maintenance of roads.

Since 1999 Masvingo has adopted an increasing block

tariff, with the first block covering consumption up to 18

m3/month per connection and the second anything in

excess, in conjunction with a fixed monthly charge. The

fixed charge is differentiated between households in af-fluent neighbourhoods and those in other areas. Due to

the unstable economic climate, the tariffs are being re-

viewed every 6 months since 2001. Table 4 shows that

the tariffs were increased significantly during 2001 and

2002. Table 5 shows that low water consumers pay a

relatively high price per cubic metre of water. This is due

to the relatively high fixed charge, which, for a house-

hold consuming only 12 m3/month, contributes 43% toits water bill. The largest water users, the affluent, pay

on average about the same unit water price as the non-

affluent users.

Income levels of the majority of residents in Mas-

vingo are not high. An oral opinion survey was carried

out which found that Z$ 3500 per month was the av-

erage cash income per household for the low-income

from

$/a)

Profit margin (%) Total revenue

council (MZ$/a)

Contribution wa-

ter account (%)

15 19.40 33

10 24.24 34

24 31.48 34

41 67.14 35

74 71.28 40

79 126.79 36

83 325.40 25

Table 4

Domestic water tariff, Masvingo, 2001 and 2002

Year Fixed charge (Z$/connection/month) Consumption (Z$/m3)

Poor Rich #18 m3/month >18 m3/month

2001 January 80 287.30 8.98 12.82

July 100 359.13 11.23 16.03

2002 January 155 556.45 17.41 24.85

July 186 667.74 20.89 29.80

Table 5

Average water price at different consumption levels; January 2002 tariff, Masvingoa

Household Monthly consumption (m3/

connection/month)

Total water bill (Z$/month) Average water price (Z$/m3) Fixed charge (%)

Non-affluent 12 364 30 43

Non-affluent 18 468 26 33

Non-affluent 30 767 26 20

Affluent 60 1914 32 29

Affluent 120 3405 28 16

a In January 2002, 1 US$ was equivalent to Z$ 55 (official rate) and Z$ 300 (parallel market rate).

Table 6

An alternative tariff structure for domestic users, Masvingo, January

2002

Block (m3/connection/month) Tariff (Z$/m3)

0–12 10.00

13–24 20.00

25–36 35.00

37+ 55.00

810 E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815

bracket (the minimum set by government is Z$ 8900 permonth). Using tariffs applicable from January 2002, and

12 m3/household/month as the average water con-

sumption in the poorest neighbourhoods, a household

would pay Z$ 364 per month, or 10% of estimated cash

income. World Bank studies have recommended that

not more than 5% of income should be spent on water

for basic requirements. The high-income consumers,

however, spend less than 5% of their income on water.Assuming an average income of an affluent household of

Z$ 60,000 per month, and average water consumption of

60 m3/month, its monthly water bill would amount to

Z$ 1914, or only 3% of household income.

It therefore appears that Masvingo’s water tariffs

could be improved: the fixed charge must go down since

it compromises equity; whereas the tariff of the second

block should be increased relative to the first block,since that would give a clear signal to high water users to

reduce their consumption. Such a change in the tariff

structure is likely to have little effect on water con-

sumption by poor households, since these have a relative

inelastic demand for water (see Section 4). However, the

tariff change would influence consumption levels of the

affluent households, which have a much higher elasticity

of demand.Dube (2002) proposed an alternative tariff structure,

which abolishes the fixed charge and introduces a four-

stepped rising block tariff structure that is based on the

same principles developed by Kaumbi (2000) for the

City of Windhoek, and justified by Savenije and Van der

Zaag (2002). The first block considers the lifeline

amount (12 m3/household/month), and its tariff recog-

nises the limited ability to pay by the poor, assumingthat the low-income bracket may not spend more than

3.5 % of cash income on water. The tariff for the second

block, the well being quantity (24 m3/household/month),

is set at the real cost of water supply. The third block

has a tariff that meets the full cost of water supply. The

tariff of the highest block compensates for the subsidies

enjoyed by the lowest two blocks, and caters for the fi-

nancial requirements of future extensions of the water

supply utility (Table 6). Table 7 compares the alternative

tariff with the January 2002 tariff.The alternative tariff yields the required revenue (in-

cluding an estimated 50% of income over and above

operation and maintenance costs, meant to cover in-

frastructure development); considers the poor’s limited

ability to pay; and gives the correct signal, namely that

with increasing consumption the average charge per unit

of water also increases.

6. Projecting Masvingo’s water demand

Three distinct demand patterns can be established inthe past 20 years in Masvingo. The patterns have arisen

as a result of the occurrence of the drought, water ra-

tioning as and when it was applied, economic growth,

rainfall and population, as was explained by the multi-

ple linear regression analysis. Projections of future water

Table 7

Comparison of domestic water bill and revenue, January 2002 tariff and alternative tariff

Water consumption block (m3/connection/month) 0–12 13–24 25–36 37+ 37+ Total/average

Average water consumption (m3/connection/month) 10 22 32 70 90 33

Number of connections (estimate) 3000 2500 2000 2000 500 10,000

Alternative tariff

Average water bill (Z$/connection/month) 100 320 640 2364 3296 955

Average water charge (Z$/m3) 10 15 20 38 42 29

Estimated revenue (MZ$/month) 0.3 0.8 1.3 5.3 1.9 9.6

January 2002 tariff

Average water bill (Z$/connection/month) 329 568 816 2162 2659 969

Average water charge (Z$/m3) 33 26 26 31 30 29

Estimated revenue (MZ$/month) 1.0 1.4 1.6 4.3 1.3 9.6

E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815 811

demand were made, assuming that the factors that in-fluenced past water use, as given by the MLR analysis in

Section 4, will remain dominant in the future. The fol-

lowing assumptions were also made:

• that gross domestic product will be positive;

• that normal rainfall seasons will occur and that there

will be no water rationing as a result;

• that the population growth of 3% per year witnessedin the past 4 years will continue.

Table 8 gives the data derived from the above as-

sumptions. These data were applied to formula (2) de-

veloped in Section 3. The results (Table 8, Fig. 6) show

that with unrestricted demand, water use will be 9.8

Mm3/a in the year 2012, or 26,800 m3/day on average.

Applying a peak factor of 1.45, the capacity of thesystem to supply treated water should be 39,000 m3/day.

It has already been shown that per capita water use in

Masvingo is relatively high, and that there is scope for

reducing this high water use by way of some demand

management measures. A further projection of water

demand was therefore made to include measures that

would decrease the demand for water. This will be im-

perative during the coming 2 years, before the currentworks are upgraded.

Table 8

Projection of unrestricted demand, Masvingo, using formula (2)

Year Input

Population (in 1000) Rainfall (mm/a

2001 71 676

2002 74 356

2003 76 600

2004 79 600

2005 81 600

2006 83 600

2007 86 600

2008 89 600

2009 91 600

2010 94 600

2011 97 600

2012 100 600

6.1. Reduction of water losses

Water losses in the city are around 15%, equivalent to

2600 m3/day. Some of these losses are a result of high

static pressures, pipe bursts, leaking valves and reser-

voirs and water treatment processes. Static pressures are

between 80 and 90 m for most of the city. It will be

necessary to reduce pressures to between 30 and 60 m, or

with some 35%. This could reduce water losses by atleast 7% (Singh, 1999), equivalent to 180 m3/day.

The leaking Cooden reservoir should also be re-

paired, saving 100 m3/day. Passive leakage surveys

which are currently not carried out, and quick responses

to reported bursts through a better equipped plumbing

department could potentially save an additional 600 m3/

day. Awareness raising campaigns for the public to re-

port leaks through 24-h-telephone contact and free offerof technical advice to repairs of leaks could provide

further savings.

6.2. Tariffs

Reducing excessive water use by affluent households

from the current average of 78–66 m3/month (by 15%)

would yield 12 m3/month per household. With 1200affluent households, the possible reduction in water use

Output

) GDP (% change) Water use (Mm3/a)

)4 6.8

)1 7.6

1 7.5

2 7.8

3 8.0

4 8.2

5 8.5

6 8.8

6 9.0

7 9.3

7 9.5

7 9.8

Table 9

Potential and short-term reduction of water demand, Masvingo

Water demand

management measure

Potential reduc-

tion of water

demand (m3/day)

Short-term realistic

reduction of water

demand (m3/day)

Reducing losses

2.000

3.000

4.000

5.000

6.000

7.000

8.000

9.000

10.000

1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011

trea

ted

wat

er (1

.000

m3/

a)

projectedobserved

MLR model

Fig. 6. Projection of demand to 2012 for unrestricted demand, Masvingo.

812 E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815

is 480 m3/day. This reduction will be possible if Council

were to adopt a rising block tariff structure as given in

Table 6. Because the response to tariff increases is not

known for the city, the impact of tariffs on quantity

consumed would need to be monitored to be able to

quantify the saving derived from this measure.

Pressure reduction 180 180

Repair Cooden reservoir 100 100

Passive leakage control 600 300

Reducing demand

Alternative tariff 480 240

Retrofitting 1540 370

Total reduction 2900 1190

Current water use 18,600 18,600

% reduction of demand 15.6 6.4

6.3. Retrofitting

Retrofitting plumbing fittings, such as installing low

volume water closets and low volume shower roses, re-

duce overall water use by at least 25% of domestic waterconsumption (Martindale and Gleick, 2001). If this were

to be effectively applied to cover 50% of all Masvingo

households, a saving of 1540 m3/day would result. One

cheap measure that can be implemented immediately is

to reduce the cistern capacity of toilets. Gumbo (1998)

estimated that water used for flushing constitutes about

30% of total domestic water use. Adjusting floats in

existing installations, or simply putting one or twostandard bricks in the cistern would reduce cistern ca-

pacity by 10% or more. Each household would reduce

its consumption by approximately 3%, equivalent to

water savings of 370 m3/day in the entire city.

Table 9 indicates the potential and short-term re-

ductions in water demand. It is estimated that through

immediate measures, water demand can be reduced with

1200 m3/day, or 0.44 Mm3/a. This reduction in demandis equivalent to the expected growth in water use during

a period of 2 years (compare with Table 8). Imple-

menting the proposed water demand measures, would

create a 2 year window to implement the next supply

option. In the longer term, with sustained campaigns

and technical and political support, the reduction in

demand may reach 1 Mm3/a, or 15.6% of current water

use. The above assumptions were translated into re-duction factors for current levels of water losses and

domestic water use, and incorporated into the water

projections (Table 10, Fig. 7). Successful implementa-

tion of these measures would imply that the water sup-

ply required in 2012 for unrestricted demand, would

only be necessary in the year 2020.

7. Conclusion

The current supply infrastructure is no longer ade-

quate to meet the water needs of Masvingo. Providingfor conventional unrestricted demand no longer makes

reasonable sense in the present day water management

strategies. This is because the water resource is no longer

abundant and the costs of putting up new water supply

infrastructure are ever increasing. For this reason it

becomes imperative for the city to provide for future

demand taking into account also water demand man-

agement measures. A consideration of demand man-agement options is necessary and these options should

run concurrent with the implementation of the supply

infrastructure. In addition, the tariff structure needs to

be reviewed, as water in Masvingo is expensive for the

poor and cheap for the rich. Moreover, it is recom-

mended that the water account be separated from other

council accounts, from which transfers can be made to

meet other council expenses only when such excess

Table 10

Projection with demand management measures, Masvingo, using formula (2)

Year Input WDM measures Output

Population

(in 1000)

Rainfall

(mm/a)

GDP (% change) Reduction factors (relative weight) Water use

(Mm3/a)Losses

(0.12)

Domestic

(0.70)

Industrial

(0.18)

2001 71 676 )4 1.00 1.00 1.00 6.8

2002 74 356 )1 0.95 0.95 1.00 7.3

2003 76 600 1 0.94 0.94 1.00 7.2

2004 79 600 2 0.93 0.93 1.00 7.3

2005 81 600 3 0.92 0.92 1.00 7.5

2006 83 600 4 0.91 0.91 1.00 7.6

2007 86 600 5 0.90 0.90 1.00 7.8

2008 89 600 6 0.89 0.89 1.00 8.0

2009 91 600 6 0.88 0.88 1.00 8.1

2010 94 600 7 0.87 0.87 1.00 8.3

2011 97 600 7 0.86 0.86 1.00 8.5

2012 100 600 7 0.85 0.85 1.00 8.6

0

2.000

4.000

6.000

8.000

10.000

12.000

14.000

1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021

wat

er u

se (1

.000

m3/

a)

current capacitystressed capacitycapacity by 2005 (with WDM)capacity by 2012 (with WDM)capacity by 2020 (with WDM)observed water useconventional projection water usewdm projected water use

Fig. 7. Projection of unrestricted and managed demand to 2022, Masvingo.

E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815 813

amounts are available, as was also recommended for the

city of Mutare by Gumbo and Van der Zaag (2002).

There is scope for instituting water demand man-

agement in the city of Masvingo. While the level of

water loss in Masvingo is not very high, it is not beyond

improvement. Water demand management measures

should be implemented forthwith so that the benefits

will be felt within the next 2 years, without having toresort to very expensive investments or incurring huge

costs. Some of the measures that can be taken immedi-

ately include:

• Awareness raising on water use and the opportuni-

ties of retrofitting of plumbing fittings––one practi-

cal measure being to reduce flushing water in the

cisterns.• Adequate staff and facilities in the plumbing section;

so that quick responses to pipe bursts are possible.

• Incentives for repairs to leaking plumbing fittings in

the homes––a practical option to council being to of-

fer free repairs or being pro-active in offering free

technical advice where required.

• Reduction of pressures by use of pressure reducing

valves in the distribution network.

• A properly structured tariff that would encourage

conservation and enhance equity.

The above measures will reduce water demand and

give Masvingo City Council a breathing space of only 2

years to increase the capacity to meet the water demand

expected in 2012, namely 27,000 m3/day (unrestricted)

or 24,000 m3/day (with demand measures). Using a peak

factor of 1.45 the supply components should be able to

cope with a demand of 39,000 m3/day (without demandmanagement) or 35,000 m3/day (with demand manage-

ment). Following the water demand management route,

814 E. Dube, P. van der Zaag / Physics and Chemistry of the Earth 28 (2003) 805–815

by 2012 a next capacity upgrade will be necessary,

namely to cope with a demand of 27,000 m3/day (with

demand management) expected in 2020.

The required investment for upgrading plant capacity

to the projected unrestricted demand in the year 2012 is

estimated to be US$ 9 million, whereas the reduced

Year Input Output Observed

Population, N Rainfall, P GDP growth,

GRationing, R Projected trea-

ted water, QTreated water

produced

Unit 1000 mm/a % 0#R#1 1000 m3/a 1000 m3/a

Constants b c d e aValues +90.2 )1.5 +26.8 )837 +1496

1977 23 600 )7.2 0.0 2495 2430

1978 25 596 )0.8 0.0 2853 2444

1979 26 604 1.4 0.0 2990 2978

1980 28 633 11.0 0.0 3384 3334

1981 29 872 10.7 0.0 3115 31381982 31 441 1.4 0.0 3679 3832

1983 33 208 )4.2 0.0 4053 4551

1984 35 459 2.6 0.0 4046 4042

1985 37 838 9.3 0.0 3849 3702

1986 39 617 1.8 0.0 4155 3998

1987 41 273 1.5 0.0 4833 4454

1988 43 857 5.9 0.0 4272 4450

1989 45 527 3.6 0.0 4876 50261990 48 681 7.2 0.0 5015 5270

1991 50 293 5.0 0.0 5707 6057

1992 52 110 )4.8 0.0 5895 5957

1993 54 756 2.9 1.0 4494 4846

1994 56 430 4.2 0.8 5357 4881

1995 58 593 )0.2 0.6 5346 5428

1996 60 794 10.4 0.4 5682 5736

1997 62 729 1.5 0.2 5887 56791998 65 390 2.0 0.0 6839 6595

1999 67 817 0.8 0.0 6358 6257

2000 69 1135 1.0 0.0 6076 6191

2001 71 676 )4.0 0.0 6798 6782

plant capacity would require US$ 5 million, a saving ofUS$ 4 million. A relatively small portion of this saving

would have to be invested in water demand measures.

The City Council could invest the remainder in other

priority areas.

Acknowledgements

This research was partly funded by the British De-

partment for International Development (DfID)

through HR Wallingford in the UK. This work is

meant to feed into a Knowledge and Research (KAR)

programme, which aims to develop a Handbook for

the Assessment of Catchment Water Demand and

Use.

Appendix A. Input and output of multiple linear regres-

sion model of water use in Masvingo, 1977–2001

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