Household Water Treatment: Are

Ceramic Water Filters a Sustainable

Intervention for Low-income

Countries? : A literature review

Supervisor: Dr. Jeroen Ensink

Candidate number: 1402062

Word count: 9,769

Project length: Extended

Submitted in part fulfilment of the requirements for the degree of MSc in

Control of Infectious Diseases

September 2015

MSc Project Report

2014-2015

1

Contents

Abstract 2

Acknowledgements 3

1.0 Introduction 4

2.0 Background 5

2.1 Diarrhoea in low-income countries 5

2.2 Aetiology of diarrhoea 6

2.3 Transmission route of pathogens 7

2.4 Brief overview of WASH interventions 8

2.5 Recommendations for quality of water 9

2.6 Household water treatment 10

2.7 Introduction to ceramic water filter and sustainability 11

3.0 Aims and objectives 12

3.1 Aim 12

3.2 Objectives 12

4.0 Methodology 13

5.0 Results 14

5.1 Table of results 16

5.2 User compliance 17

5.3 Filter longevity 20

5.4 Willingness-to-pay 21

5.5 Accessibility to replacements/spare parts 22

5.6 Health impact 22

6.0 Discussion 23

7.0 Conclusion/Recommendations 30

Reference List 31

2

Abstract

Diarrhoeal disease remains to be the second biggest killer of children under 5 worldwide yet

can be easily prevented through water, sanitation and hygiene interventions. Since 2002,

World Health Organisation has promoted the use of household water treatment that increases

water quality in the household helping to reach the millennium development targets. Ceramic

water filters is one such household water treatment technology that reduces turbidity and is

highly efficacious at removing pathogens. With the arrival of the sustainability development

goals, this literature review aimed to investigate and analyse the sustainability of ceramic

water filter interventions by focusing on five key aspects that affect sustainability; compliance,

filter longevity, willingness to pay, accessibility and health outcomes. Search found a total of

945 papers of which 10 were deemed suitable for review. The quality of the studies were

relatively low with none assessing all of the five desired outcomes. Study design consisted of

randomised control trials and cross-sectional surveys. The longest time since distribution was

4 years with most studies having a relatively short time frame therefore limiting our

understanding of long-term ceramic water filter sustainability. Notable gaps in the literature

were identified namely that there was no research on the long-term benefits of CWFs.

Evidence for effectiveness of CWFs was inconclusive due to inherent biases of the RCT

design. The review concludes that further research on the effectiveness of ceramic water

filters on reducing diarrhoea be conducted as well as more studies that identify major barriers

that prevent a sustainable ceramic water filter intervention.

3

Acknowledgements

I would like to, first and foremost, express my sincere gratitude for all the help and support

from my tutor and supervisor Dr Jeroen Ensink. Thank-you for introducing and teaching me

about the subject and for your guidance throughout the project.

A big thank-you to my fellow students for being such great company during the long library

hours. And finally to my parents for helping me to stay focused and calm.

4

1.0 Introduction

Diarrhoeal disease is both treatable and, more importantly, preventable yet 760,000 children

under five die from it every year(1) although this figure is sometimes estimated to be as high

as 1.3 million per year(2).

In 2000, The United Nations (UN) established the Millennium Development Goals (MDG) to

which all 193 UN member states committed to achieve. MDG7 focused on ensuring

environmental sustainability namely to halve by 2015 the proportion of the population without

sustainable access to safe drinking water and basic sanitation. The global target of safe

drinking water was supposedly met in 2010 five years ahead of schedule, with current

estimates standing at 91% of the global population using an improved drinking water

source(3). Although this declaration is arguably over estimating figures since the methodology

used for monitoring progress has not incorporated the core components – “sustainable”,

“access” and “safe” – of the MDG7 water target(4).

Improvements in urban areas, through piped water systems, are more straightforward than

the less accessible rural areas. Currently eight out of ten people without access to improved

water source live in rural areas(3). It is in these remote and expansive areas where more

durable options for the provision of safe drinking water must be focused in order to increase

communities’ access and decrease early childhood mortality. In 2002, World Health

Organisation literature review recognised household water treatment (HWT) as an achievable

and low-cost approach for increasing water quality and reducing early childhood diarrhoea

(ECD)(5).

With the end of the Millennium Development Goals and the beginning of Sustainable

Development Goals, more emphasis is being placed on development which is maintainable

thereby securing future generations livelihoods(6). Target 6.1 of the SDGs aims to achieve

universal and equitable access to safe and affordable drinking water for all by 2030.

Sustainability is defined as the maintenance of processes at a certain level, a concept that is

vital for a successful WASH intervention with prolonged optimal health outcomes. Whilst the

explanation of sustainability for development remains broad and ambiguous, it is usually

broken down into three non-distinct dimensions: social, economic and environmental. In order

to achieve these three aspects of sustainability, WASH interventions and the technology used

must therefore in itself be maintainable. This review focuses on sustainability of the ceramic

water filter (CWF) and main themes surrounding user compliance in order to evaluate its future

prospects in development.

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2.0 Background

2.1 Diarrhoeal Disease in Low-income Countries

Diarrhoeal diseases account for one in nine child deaths worldwide killing approximately 2,195

children every day the majority of which occur in low-income countries. It is defined as the

passage of 3 or more loose or watery stools per 24 hours, usually the body’s response to

gastrointestinal infection. Most vulnerable are under 5s, pregnant women, elderly and immune

deficient. Immediate effects of diarrhoea are loss of fluid initiating severe dehydration, loss of

electrolytes and, in extreme or persistent cases, death. Diarrhoea is a significant contributor

of malnutrition due to the loss of nutrients in the stool as well as causing degeneration of the

intestinal gut wall. Particularly for those in poverty with limited access to a nutritional diet,

especially zinc, this malnutrition decreases immune response which further increases risk of

gastroenteritis thus establishing a vicious cycle(7) (see figure 1). As the diarrhoea-malnutrition

cycle intensifies, children become prone to other infectious diseases consequently

contributing to the majority of early childhood deaths either directly or indirectly.

Figure 1: Relationship between malnutrition and diarrhoea illustrating the vicious cycle. Image taken from: Ghai. O. P. Understanding and managing acute diarrhoea in infants and young children. [online]. Available at: http://hetv.org/pdf/diarrhoea-india3.pdf

Not only are the immediate effects of diarrhoea a major public health concern, the long-term

effects of continuous malnutrition from enteritis hinders both growth and cognitive

development not to mention the number of school or work days missed due to illness. As well

as personal loss of income, health sector cost puts a major financial burden on government

placing even more strain on an already fragile system. Globally, diarrhoeal disease accounts

for approximately 3.6% of disability adjusted life years burden illustrating its significance in

public health(8).

Maintaining electrolytes is essential for treatment of diarrhoea and oral rehydration sachets,

praised as the most important medical advance of this century, are not only effective but also

economically viable and accessible for communities in low-income countries. Although

6

treatment reduces the mortality of diarrhoeal disease, more focus needs to be placed on

reducing morbidity by preventing the acquisition of waterborne pathogens through water,

sanitation and hygiene (WASH) interventions. In this way, reducing the number of diarrhoeal

disease episodes will increase nutritional status of children increasing quality of life and

reducing long-term damages associated with diarrhoea.

2.2. Aetiology of Diarrhoea

Pathogens that can be transmitted through contaminated water vary according to

characteristics, pathogenicity and behaviour. The three classes of pathogens of common

public health concern are protozoa, bacteria and viruses. All are unique in size, structure,

biochemical make up and virulence.

Oocysts of Cryptosporidium alongside the cysts of Giardia are the main protozoa causing

diarrhoea in low-income countries. These structures are incredibly persistent in water due to

their resilient structure which only breaks down after consumption in stomach acid of the host

to cause infection.

Bacterial pathogens of significant importance include Escherichia coli, Campylobacter jejuni,

Vibrio cholera and Shigella dysentriae. Variation in infectivity, pathogenicity and dose

response is diverse amongst the bacteria class. For example, Campylobacter is relatively

common with a low mortality rate, conversely E. coli O157 is far less common and infection

can more severe reactions through haemolytic uremic syndrome and potentially death(9).

Cholera has a fairly high infective dose whereas the infective dose of Shigella is very low with

at only 10-100 organisms(10).

Critical waterborne viruses include rotavirus and norovirus. Whilst the former is more

widespread globally, the latter is typically associated with outbreaks in developed countries

within enclosed living conditions such as cruise ships.

The importance of different pathogens varies according to seasonality, geographical location

and conditions(9). For example, cholera most commonly presents as a sudden outbreak and

associated with natural disasters or overcrowded and unsanitary living conditions such as

refugee camps. On the other hand, rotavirus is present in almost all settings with the global

burden of disease amongst children hospitalized relatively evenly spread between WHO

regions, although 95% of deaths occur in low-income countries of Africa and Asia(11).

7

2.3 Transmission routes of pathogens

It is estimated that 94% of the burden of diarrhoeal disease is due to the environment and

associated with risk factors such as unsafe drinking water and hygiene(12). Enteric pathogens

transmit from host-to-host most commonly through the faecal oral route easily exacerbated in

settings where there is low sanitation and hygiene. The transmission of waterborne pathogens

from faeces to ingestion is best represented in the F-diagram (see figure 2).

Barriers to prevent these transmission routes clearly require an integrated approach.

Appropriate sanitation prevents the first stage of transmission of faecal pathogens to the

environment. Secondary barriers focus more on protecting a potential new host from ingesting

pathogens by increasing water quantity, hygiene and water quality. Although consumption of

contaminated water poses the greatest risk, it is important not to forget other water related

infections (see table 1). Although the transmission of these pathogens does not take the

faecal-oral route, appropriate WASH interventions have the power to significantly impact on

lowering the incidence of disease.

FAECES

Fluids

Fields

Flies

Fingers

Food New Host

Water Quality Sanitation

Water Quantity Hand-washing

Figure 2: The F-diagram illustrating various pathways of the faecal-oral route and WASH interventions barriers of transmission

8

Transmission Description Example WASH intervention required

Faecal-oral Ingestion of contaminated water

Giardia, cholera, rotavirus

Improved water quality

Water-washed (water scarce)

Person-person transmission due to poor personal and domestic hygiene

Trachoma, conjunctivitis

Increasing quantity of water or access to water

Water-based Transmission through aquatic host

Schistosomiasis, guinea worm

Increasing water quality at the source

Water-related insect vector borne

Disease transmission through vectors that rely on water for breeding

Malaria, Yellow fever

Improved sanitation or drainage system

Table 1: Bradford classification of water-related diseases(13).

2.4 Brief overview of WASH interventions

Access to water, sanitation and hygiene is key for local and international development not only

in public health but also in socioeconomic improvement, gender equality, education and crop

productivity. WASH interventions aim to block all or some transmission routes and so

decrease the incidence of diarrhoea. They can be a challenging mission requiring education,

human behaviour change, a secure initial investment and cooperation from beneficiary

communities at all levels. The ideal WASH intervention should involve local communities in

decision-making and production that gives them a sense of ownership and increasing

likelihood of continued maintenance. In high-income countries, piped water systems, allowing

the efficient removal of wastewater and continuous delivery of safe and clean water, are seen

as the gold standard for optimal sanitation and hygiene. In low-income countries, with widely

dispersed rural communities or expanding and overcrowded informal urban settlements, piped

water systems are simply too unrealistic given the initially high investment and continuous cost

of maintenance. Governments also refuse to recognise illegal city dwellings as deserving of

piped water systems even though these communities are most in need of proper sanitation

and water supply.

WASH interventions have therefore adjusted to meet the needs of the most impoverished and

unreachable communities often focusing on one aspect of WASH at a time. Traditionally,

interventions have mainly centred on improving water quality since this is the main route of

transmission particularly where rates of diarrhoea are high. Water quality interventions aim to

protect or treat water for the removal of microbial contaminants. However it is argued that

improving water quality at the expense of water quantity may in fact be counterproductive in

reducing incidence of diarrhoea(14). Nevertheless, results have shown improving the quality

9

of water, especially at the household level, is more effective at reducing diarrhoea than other

WASH interventions(15).

2.5 Recommendations for Water Quality

Although safe drinking water is recognised as a basic human right, there are no internationally

recognised standards of drinking water. For countries with no official requirements for water

quality, World Health Organisation has provided universally recognised guidelines. WHO

guidelines state that the tolerable burden of disease is defined as an upper limit of 10-6 DALY

per person per year. In terms of household water treatment, performance is measured by

treatment requirements in relation to source water quality. The value, expressed as log10

reduction in microbe concentration (LRV), is measured using the three reference pathogens:

Campylobacter jejuni, Cryptosporidium and rotavirus(16). Unfortunately in most settings,

particularly low-income settings, this high 10-6 DALY per person per year is unachievable

therefore a tiered approach to assessing treatment technologies is used. The top tier or “highly

protective” water treatment technologies can achieve 10-6 DALY per person per year if there

is consistent performance for a whole year

(see table 2).

Table 2: Tiered approach of the recommended levels of performance for bacterial, protozoal and viral reduction(16).

Clearly the first tier of “highly protective” should be used whenever possible however

“protective” tier is also known to achieve significant health benefits in areas with high burden

of waterborne disease. Only in exceptionally difficult circumstances should the “interim” be

used and as such should only be seen as an incremental step towards reaching the higher

tiers. The targets can only be achieved when household water treatment technology is

consistently used in order to receive the full health benefits.

2.6 Household water treatment

The objective of household water treatment (HWT) is to allow for the treatment of water in the

home before use. Point-of-use (POU) treatment provides the benefits to recipients of more

ownership and control over their water quality in the household. The risk of recontamination

during transport between water source to point-of-use or through inadequate storage is high,

Tier Log10 reductions in bacteria

Log10 reductions in protozoa

Log10 reductions in viruses

Health based target (DALY)

Highly

protective

≥ 4 ≥ 4 ≥ 5 10-6

Protective ≥ 2 ≥ 2 ≥ 3 10-4

Interim Protective removal of two classes of pathogens with a proven effect on reducing

diarrhoeal disease incidence.

10

particularly in cases where source water has low bacterial count(17). HWT can therefore

address both of these problems. Cochrane review of thirty HWT randomised control trials

show on average a 50% reduction in diarrhoea morbidity when interventions to improve water

quality were given at the household level rather than at the source(18). Furthermore, meta-

analysis reveals that point of use treatment is more effective at reducing diarrhoea by 0.79

(0.63-0.98) whereas treatment of water at the source has minimal effect at 0.95 (0.9-1.0)(19).

HWT can either physically inactivate microorganisms through boiling, solar disinfection

(SODIS) and filtration or chemically degrade microbes typically using chlorine as a germicide.

Boiling, the most traditional form of point of use treatment, requires a continuous rolling boil

for 10 minutes before it can denature the proteins of pathogens. Although very effective at

removing microbes, this method does require the constant need for fuel/firewood which may

be costly to the user. Chlorination provides a quicker alternative, commonly used in disaster

or waterborne outbreak settings, which can be easily implemented and monitored. This

method is also an efficient solution for safe storage since residual chlorine in the containers

protects from recontamination. However getting the correct dilution is challenging since too

little is ineffective and hyperchlorination, a common problem, is damaging for health. Solar

water disinfection (SODIS) method involves placing water in direct sunlight between 6-48

hours allowing the combined effect of solar heat energy and UV radiation to act as

germicide(20). Although simple to use and low-cost, the practicalities of SODIS are sometimes

not realistic in settings with unpredictable weather patterns and seasonality. In addition, water

must be consumed within 24 hours before risk of recontamination increases. The main

drawback of both chlorination and SODIS is the decline in microbicidal activity as source water

turbidity increases. Suspended matter physically shields the pathogens from chemical or UV

damage and, together with boiling; these methods have no effect on turbidity. Filtration,

although more costly, is the only method to address turbidity as it physically blocks the

movement of suspended particles into the effluent. Biosand filtration requires a container filled

with varying sizes of granules all below the recommended 0.7mm size that effectively filters

microbial contaminants(21). Maintenance of the biosand filter is minimal and is therefore a

good candidate when choosing household water treatment although the weight of the vessel

makes it difficult for mobile households as well as a large initial cost because the sand is not

normally available locally in low-income countries.

2.7 Introduction to ceramic water filter and sustainability

CWFs are typically manufactured by mixing clay and finely grounded burnout materials,

moulded into shape and kilned eventually producing a hardened container with a specific

11

range of pore sizes usually within the range of 40μm. Such a simple manufacturing process

allows for many moulds to form varying sizes and shapes, most common being a candle or

pot (see figure 3). Few raw materials are needed for CWF manufacturing and can be sourced

locally in most low-income countries, only the kiln needs a specialist and colloidal silver must

be imported.

The pores created within the ceramic material act by physically blocking the passage of

parasites and solid particles by size exclusion as well as absorbing bacteria. Significant

improvements are seen when colloidal silver or silver nitrate, toxic to bacterial cells, is painted

on the inside of the filter(22). The silver nanoparticles interact and disrupt the cell wall of

bacteria acting as an effective microbicide. CWF are ideal for low-income settings since the

filters can last between 6 months and 1 year without the need for a power source. After a

certain amount of time, usually one year although changes according to design, the ceramic

filter component will need to be replaced. Filter efficacy, under both laboratory conditions and

in the field, consistently show efficient removal of pathogenic bacteria, protozoa and

viruses(23). The wide variety in design and the ease of the manufacturing process means

CWFs can adapt according to settings and needs of the beneficiaries. The ceramic water filter

(CWF) has, in recent years, received wide universal coverage with most interventions

occurring in Cambodia. NGOs such as Potters for Peace promote its usage globally and assist

in establishing factories and workshops(24). Although the health benefits of drinking clean

water from CWFs seem obvious, there is little literature on its effectiveness and, even more

importantly, no research on whether the CWF is a feasibly sustainable intervention. An

essential part of a successful intervention is its ability to self-sustain beyond the

implementation efforts of NGOs. Human behaviour change, or compliance is needed for this

to happen particularly in CWF interventions. Whilst sustainability relies on filter endurance,

continuous compliance by user and demand for replacements is also key. Since the filter

component must be replaced, willingness-to-pay and access to these parts is essential. Finally

all of these aspects must combine to produce the ultimately ideal outcome of continuous

reduction in diarrhoeal disease in particular early childhood diarrhoea ECD.

Figure 3: most common shapes for ceramic water filters

12

Three key aspects can directly affect compliance: filter longevity, willingness to pay (WTP)

and access to spare parts. In turn health outcomes of a CWF are totally reliant on compliance

of the user (see figure 4).

Figure 4: A conceptual framework of sustainability.

3.0 Aims and objectives

3.1 Aim

The aim of this review is to assess whether ceramic water filters are a long term solution to

improving water quality by evaluating it effectiveness in reducing diarrhoeal disease whilst

focusing on five key indicators of sustainability.

3.2 Objectives

Investigate uptake and acceptance of CWFs by assessing the literature on compliance

of recipients

Investigate whether CWF is a durable technology that can maintain a high level of

performance for a prolonged period of time

Assess the demand for CWFs by examining willingness-to-pay for replacements/spare

parts

Assess to what extent access to spare parts/replacement component can affect the

sustainability of a CWF intervention

4.0 Methodology

Assessing the sustainability of ceramic water filters requires, not just looking at the beneficial

outcomes, but also evaluating the steps involved in implementation of an intervention including

factors associated with compliance (see figure 4). This conceptual framework was used for

the basis in evaluating the literature and therefore sustainability of ceramic filter interventions.

Compliance

Willingness to Pay

Accessibility to spare parts

Filter longevity

Health Outcomes

13

Search terms used: “ceramic water filter” against “household water treatment”. Databases

used were PubMed, Web of Knowledge and Google Scholar with relevant additional records

identified through citations in other papers. The key inclusion criteria were: i) implementation

of a ceramic water filter intervention ii) outcome of at least one of the 5 key concepts. Exclusion

criteria were: i) research papers published before 2000 ii) systematic reviews

After identifying records through database searching and citations from other sources with

duplicates removed, papers were initially assessed on the relevance of their title. Titles that

specified research on either effectiveness of CWF in reducing diarrhoea or one of the key

concepts of sustainability were further assessed for eligibility. Abstracts were then analysed,

excluding any studies that did not perform research in the field or did not collect primary data.

14

5.0 Results

A total of 645 citations were identified from Web of Knowledge (694), Pubmed (92) and Google

Scholar (159) with an additional 18 from recommendations of articles submitted for

publication. After removal of duplicates, 612 articles were screened for titles and abstracts

giving 36 full-text eligible articles. Study sites of all 10 papers ranged from Asia (5), Latin

America (4) and Africa (1). No research investigated all five indicators of sustainability.

Quality of study was determined by the number of outcomes measured:

High: Paper covered 4-5 outcome measures

Medium: Paper covered 3 outcome measures

Low: Paper covered less than 3 outcome measures

Records identified through database

searching (n=945)

Records after duplicates removed (n=612)

Records screened (n=612)

Records excluded (n=591)

Additional records identified through other

sources (n=18)

Full-text articles assessed for eligibility

(n=21)

Full text articles excluded (n=11)

Not measuring any of the 5

key concepts=8 Not perform research in the

field=3

Iden

tifi

cati

on

S

cre

en

ing

E

lig

ibilit

y

Inclu

ded

Studies included for qualitative synthesis

(n=10)

15

Using quality assessment, three papers were of a high quality as they investigated 4 of the

indicators with one of medium quality. The majority (60%) however were of low quality since

they had only researched 2 or less outcome measures (Table 1). User compliance (A) was

measured in 7 papers, filter longevity in 4, accessibility (D) in 5 and health outcomes (E) in 4.

Willingness to pay was investigated in 2 with an additional paper discussing willingness to pay

of study participants in an unpublished affiliated research paper. Only two study designs were

used of which 7 used randomised control trials (RCT) and 4 used a cross-sectional survey.

All research that measured health outcomes used a RCT design (5) which was also used to

measure compliance in two papers. Cross-sectional survey produced the high quality papers

since two that used this approach provided four outcome measures and another two gave

three outcome measures [Clasen 2006 only used cross-sectional survey for compliance (A),

filter longevity (B) and accessibility (D)].

16

5.1 Table of Results Author Study Setting Time Frame Ceramic Filter

Type Sample Size Outcome

measures Results Quality of

research

Brown 2008(25)

RCT Rural Cambodia Bi-weekly HH visits for 18 weeks

CWF & CWF-Fe manufactured by Resource Development Int.

180 (60 received CWF, 60 received CWF-Fe)

A, E A: 98% of filters were in use during visit. E: Longitudinal prevalence ratio=0.51 (0.41-

0.63) for original RDI design with a 49% mean reduction in diarrhoeal disease. CWF-Fe gave LPR=0.58 (0.47-0.71). No significant difference on health impact between the two filter designs.

LOW

Brown 2009(26)

Cross-sectional survey

Rural Cambodia 1 visit after approximately 4 years

International Development Entreprises & Resource Development Int.

50 HHs across 13 villages

A, B, C, D A: 31% filters in regular use after 4 years. 2%

decline in use per month after implementation. The OR of finding a filter still in use every 6 months=0.56 (0.5-0.63). Average length of use=2 years. B: 65% of filters not in use reported breakage

with 5% stating filter was too slow. C: 43% of HHs with disused filters were willing

to purchase an additional filter. Mean WTP for whole new filter amongst those who stopped using filter=US$2.38. Mean WTP for filter insert among users=US$2.50 (actual cost of filter insert=US$2.50-5.00). D: 13% of filters in regular use had been

replaced. 26% of all HHs did not know where to buy replacement. Study concludes that decline in usage is largely owed to filter breakage. Advise scaling up accessibility to spare parts.

HIGH

Casanova 2012(27)

Cross-sectional survey

Post-tsunami Sri Lanka

1 survey after approximately 2 years

Not Specified 4 HHs A, B, C, D A: 76% filters were still in use. B: No HHs reported a broken filter in

questionnaire. Mean flow rate=1.12L/hr. 31% filters at recommended flow rate by manufacturer, 61% (<1L/hr) below and 8% above (>3L/hr) C: 88% willing to buy a replacement filter if

needed. Mean WTP for a whole new filter=US$6.75. Actual cost of filter is not given. D: 63% believed they could not get filter in

their area and 36% did not know. 98% did not know of a place to buy filter/replacement.

HIGH

17

Author Study Design

Setting Time Frame Ceramic Filter Type

Sample Size Outcome Results Quality of research

Clasen 2004(28)

RCT Rural Bolivia Visits at 6 week intervals for 6 months

Katadyn Ceradyn™ 50 HHs (C), D, E (C): Mean WTP for whole new filter=US$9.25.

Actual cost=US$25.00. D: Spare parts left with community leaders but

no HHs had replaced them. E: Risk of diarrhoea decreased by 70% in

CWF group with OR=0.29 (0.13-0.65). Risk of diarrhoea for <5 age=83% with OR=0.17 (0.06-0.49)

LOW

Clasen 2005(29)

RCT Rural Colombia 6 months Katadyn® candle 140 HHs E CWF reduced prevalence of diarrhoea by 60%. OR=0.40 (0.25-0.63). Although results were only statisically significant at one site.

LOW

Clasen 2006(30)

Cross-sectional survey

Post-flooding Dominican Republic

Survey 16 months after distribution

Ceramica Stefani/First Water

115 HHs A, B, C/D A: 48.7% still in use. B: 22 (19%) candle filters broken, 6 (5%)

clogged, 4 (3%) leaking of GAC into effluent. Average period of operation was 9 months. C/D: Replacements were made accessible to

all participants at $4.50. Of filters still in use, 62% had replaced the candle element.

MEDIUM

Clasen 2006(31)

RCT & Cross-sectional survey

Rural Bolivia RCT: 5 visits over 5 months Survey: 1 visit after 9 months

Katadyn® candle Stefani® candle

RCT: 60 HHs (20 received Katadyn®, 20 received Stefani®)

A, B, D, E A: 67% of filters regularly used after 9 months,

13% were occasionally used, 21% not in use. B: Of those not in regular use, 25% were

broken, 31% said filter was too slow. D: Replacement candles not available locally so

users were not cleaning as much. E: CWF reduced prevalence of diarrhoea by

45.3% giving an adjusted OR=0.49 (0.24-1.01). No statistically significant difference found for <5 age group.

HIGH

Du Preez 2008(32)

RCT Rural South Africa and Zimbabwe

Pictorial diary used over 6 months

British Berkefeld® South Africa: 56 HHs (29 received filter) Zimbabwe: 58 HHs (31 received filter)

E CWF reduced incidence of bloody and non-bloody diarrhoea by 80%. RR=0.21 (0.12-0.36).

LOW

Ensink 2015(33)

RCT Displaced communities, Pakistan

1 survey 6 months after distribution

Stefani® 3,075 (78 received filter)

A, B A: No CWF in use after 6 months B: 30% were broken after 6 months. Study

proposes that CWF do not usually last longer than 2 months

LOW

Luoto 2011(34)

RCT Urban Bangladesh

1 visit 2 months after distribution

CrystalPur Filter 800 (600 received filter for 2 months on rotation)

A, C A: Average of 29% (25-32%) self-reported

using the CWF after each 2 month trial period. The CWF was the most successful intervention compared to chemical disinfection products.

LOW

18

5.2 User compliance

Seven papers included user compliance by calculating the proportion of filters still in use after

distribution.

One four-armed randomised control trial compared three different chemical products and a

CrystalPur siphon filter in where three intervention groups received a product in randomised

order every 2 months (34). The ceramic water filter proved to be the most popular although

only with an average of 29% (25-32%) of filters still being regularly used after 2 months. One

of the paper’s main aims was to investigate barriers to usage of POU products, using an open-

ended question, which was not detailed in the results. Only the two most common reasons for

discontinuation were provided for all products one of them being that the filter took up too

much time with 27% of users choosing this option. Although whether the filtration of the water

was too slow or that the maintenance of the filter took up too much time remains to be seen.

Furthermore, no details have been provided for the number of people willing to participate

bringing into question the reliability of the study.

An additional RCT was conducted in rural Cambodia with a high compliance of 98% during

18week time frame. This high compliance can be due to the biweekly visits conducted during

the intervention trial. This may have appeared to increase user compliance through courtesy

bias since investigators visited households on a regular basis.

In Bolivia, after first assessing health outcomes of ceramic filters during the 5 month RCT trial,

a follow-up visit after 9 months was conducted resulting in 67% of HHs still regularly using the

filter, 13% in occasional use and 21% not using filter at time of visit(31). The methodology

used for categorising the filter compliance status has not been made clear particularly the

definition of occasional use making it difficult to clearly interpret compliance. Reasons for

discontinuing using the filter were mainly caused by filter being too slow (31%) or the filter

broke (25%). The design of the study involved a three-armed RCT with two different candle

designs and a control. No distinction has been made between the two different types of

candles that were initially distributed which would have been useful for assessing compliance

individually however would have reduced the power of the study given that the sample size

would have decreased.

A cross-sectional survey approximately 4 years after distribution of CWF in Cambodia with a

relatively large sample size of 405 households was able to give a more accurate picture of

long-term sustainability(26). Compliance was measured as percentage of filters remaining in

household use as a function of time resulting in a calculation of 2% decline in usage per month

(see figure 5). Using logistic regression, declining odds of 44% every 6 months of finding a

19

filter still in use was calculated with an odds ratio of 0.56 (0.5-0.63). The data was collected

from several interventions therefore has not considered the heterogeneity of implementation

methods used such as differences in education or prices charged for water filter. The paper

concludes that the most important predictor of compliance was time since implementation.

When controlled for time since implementation, the most important factors to increase filter

usage were initial investment in technology (OR=2.1 95%CI 1.2-3.7) and access to household

latrine (OR=2.4 95%CI1.5-4.0).

Figure 5: Graph showing the decline of percentage of filters remaining in household use in 6 month increments. Image taken from: Brown. J. et al. 2009. Sustained use of household-scale water filtration device in rural Cambodia.

In contrast, research in Pakistan has shown a much more rapid decline in filter usage (33).

CWFs were used as the control for this RCT therefore limited information on factors affecting

user compliance is limited. Although initially slightly resembling Brown et al’s 2% decline with

10% not using in the first 3 months, there is a rapid drop in usage after 3 months with 65%

reported to have stopped using the filter between 3-5 months after distribution until eventually

no households were using the filter after 6 months. This information is prone to bias since only

one visit could be carried out after 6 months and it solely relied on recall when filter stopped

being used.

A cross-sectional survey investigating CWF after post-tsunami Sri Lanka found that a much

higher 76% of beneficiaries were still using the filter, although the research paper has not

stated specifically how long after distribution the survey took place, it is estimated

approximately 2 years post implementation(27). The definition for a filter user included if they

had reported using within the last month possibly to account for seasonality (5% of

respondents). Although this is a low proportion and may not have affected the results, a more

accurate figure may have been to exclude this 5% since they may not be regular users. No

20

questions were asked to those who had stopped using the filter as to why, which would be

useful in identifying reasons for discontinuation however amongst the users, the most common

complaint was that the flow rate was too slow (14%).

A cross-sectional survey after 16 months conducted in Dominican Republic severe flooding

found a relatively low compliance with only 48.7% CWFs still in use(30).

5.3 Filter Longevity

No papers specifically looked at filter durability in the field however four papers have recorded

breakage with one measuring flow rate.

During a 9 month follow-up visit as part of an RCT in Pakistan, 30% of filters were found to be

broken with the research estimating the average lifespan of the Stefani® as not much longer

than 2 months(33). Filters in the households were examined by investigator and found that

breakage was associated with tightening of the saturated filter that prevents leakage from the

top to the bottom.

During the cross-sectional survey in Cambodia, of the households using the filter, 214 reported

breakage(26). This figure calculates that 42% of the households included in the study had

breakage. In addition, filter breakage appears to be the primary reason for discontinuation

since 65% of non-users reported the filter as broken.

On the other hand, data collected for cross-sectional survey in Sri Lanka found that no

households selected the ‘filter broke’ option(27). A surprising result given that this research

was carried out approximately 2 years post implementation. Filter flow rates were also

measured from 343 households giving a mean flow rate of 1.12L/hr (range 0-5.9). Only 31%

of filters fell within manufacturers guidelines for flow rate of 1-3 L/hr and 61% of filters’ flow

rate was <1L/hr. Unexpectedly, 8% of filters had a flow rate greater than 3L/hr although this is

believed to have been due to cracking in the ceramic vessel reported by households. This,

once again, brings into question the classification of ‘broken’. The fact that the paper reports

some ceramic vessels have cracked yet also concludes that no filters are broken is unclear.

An improvement may have been close inspection of CWF allowing the investigator to classify

the filter as either broken or not rather than relying on recall of household.

The cross-sectional survey conducted in post-flooding Dominican Republic found 22 (19%)

filters were no longer in use due to breakage again making this the main reason for

discontinuation since 65% of filter not in use were because of breakage. 6 filters were found

to have clogging whilst 4 leaked granular activated carbon from the filter core into the effluent

21

water. Of the filters that were broken, a common reason was that the filter had been knocked,

or that it occurred during cleaning/replacement.

5.4 Willingness to Pay

Three papers investigated willingness to pay with one discussing unpublished data of an

analogous paper.

Although Clasen et al. did not conduct the research on WTP in Bolivia, the results of a

corresponding paper using the same intervention are discussed briefly(28). When asked to

estimate cost of filter, households were fairly accurate ($24.18) however when asked on their

WTP, mean response was considerably lower than the cost of the total filter system ($9.25).

Results do not show the cost of the ceramic candle replacement component nor is any data

given on willingness to pay for the spare part, which is the most important aspect given that

only the ceramic parts need replacing regularly.

Alternatively, Brown et al’s follow-up study in Cambodia does include WTP specifically for the

replacement component(26). WTP results were measured separately for those who had

discontinued usage and those regularly using the filter. By asking an open-ended question on

an appropriate price for the whole CWF to those who stopped using the filter, mean response

was US$2.38 (US$1.48-2.95). Only 21 households reported that they had replaced their filter

after breakage. For households in regular use of a filter, method of assessing WTP for just

ceramic insert involved choosing an option rather than an open-ended question. 72% were

willing to pay for the lowest price (US$2.50) however only 26% were willing to purchase the

highest price (US$5.00). The actual price of ceramic insert is between $2.50-5.00. For those

that had discontinued use of filter, odds of willing to purchase an additional filter increased by

3.1 (1.6-6.0) when filter had been initially purchased rather than given to them for free.

In the Sri-Lankan cross-sectional study, Casanova et al. found a relatively high 88% willing to

buy replacements or spare parts if needed although this was only asked to the households

who were already regularly using their filter(27). A better understanding of demand and WTP

would be to incorporate those who had discontinued use of filter and understand if there was

still a demand even though filter was no longer in use. Only one household claimed to have

successfully replaced a filter with 7% reporting they had bought spare parts. This

demonstrates that there may be not such a high demand or willingness to pay amongst those

that discontinued filter use. Using an open ended question, the mean WTP response for a

whole new filter amongst filter users was USD$6.75. No information is given on the average

price of a CWF therefore no inference can be made on how realistic this response.

22

In the Dominican Republic survey, the paper states that ceramic candle components were

made accessible to all recipients at the price of US$4.50. Of those that still had a filter in use,

62% had successfully replaced it demonstrating a relatively high demand from users.

5.5 Accessibility to Replacement/Spare Parts

Four studies had incorporated accessibility into their research. The RCT conducted in rural

Bolivia made clear in the methodology that “spare candles, buckets and taps were left with

community leaders”(28). However a third of intervention households had filters that were

broken during the 6-month trial period. More information is needed as it remains to question

whether the spare parts were not actually accessible to the users or whether the users had

been trained in replacing components.

The cohort survey conducted in Cambodia found that, although distribution points for

replacement filter and parts were present in all study provinces, only 26% actually knew where

to purchase them from(26). However whether these distribution points were feasibly

accessible to the users remains unknown.

Similarly, Sri Lankan survey found that only 5/345 (1%) households knew that they could get

a new filter in their area whilst 63% believed they could not and 36% did not know(27).

In studies where no accessibility to spare parts was a common concern of the users and, as

a consequence, user were avoiding regular cleaning for fear of breaking it(31).

5.6 Health Impact

Five papers researched the health outcomes of using ceramic water filter, all of them looking

at diarrhoea incidence.

Research in Bolivia assessed the effect of ceramic filter on diarrhoea incidence used relied on

5 visits over 5 months where female head of household was asked to recall episodes of

diarrhoea among all household members in the past 7 days allowing diarrhoea to be calculated

as period prevalence. An odds ratio of 0.49 (0.24-1.01) shows a slightly protective effect

although the confidence interval overlaps 1.00 so is considered to have no significant

effect(31). Additionally no significant difference was found for children under 5 years of age.

CWF also reduced prevalence of diarrhoea by 45.3% in the intervention arm. While the

intervention group was divided to receive two different types of ceramic filter, no analysis on

the individual effectiveness of the filters was completed, possibly due to the subsequent

reduction in sub-group sample size and thus power of study.

23

Another RCT in rural Bolivia, using a similar methodology of recall and monthly visits but with

Katadyn CeradynTM filter, produced an adjusted OR of 0.29 (0.13-0.65) and a 70% reduced

risk of diarrhoea in the intervention group(28). As expected, a more protective effect was seen

in under 5 age group with a 88% reduction in prevalence of ECD associated with and OR of

0.17 (0.06-0.49).

By contrast, an RCT in Colombia using the same filter yielded a lower adjusted OR of 0.40

(0.25-0.63)(29). Although producing statistical difference overall, out of the three study sites

only one showed a significant odds ratio individually.

All three of the aforementioned RCT trials relied on recall of diarrhoeal disease episodes in

the past week since time of visit. Increasing the accuracy and possibly reducing courtesy bias

would be to use a pictorial diary whereby participants mark the days one person in the

household has diarrhoea. An RCT for CWFs used just that methodology producing a relative

rate of 0.21 (0.12-0.36)(32).

Discussion

The aim of this study was to assess to what extent CWFs are a sustainable intervention for

low-income countries by assessing literature on its effectiveness in reducing diarrhoea and

evaluating five key aspects of sustainability, providing recommendations to policymakers and

future implementers.

The review identified ten studies that were deemed suitable for analysis and review. The large

majority of the papers were of low quality with no study identified that presented findings on

all five aspects of sustainability.

The most notable gap in the literature was the lack of studies on the long-term effects of a

CWF intervention. Only two studies left a considerable time after filter distribution in order to

assess it sustainability (26, 27). However no papers investigated whether use of CWFs will

provide continuous beneficial outcomes for a prolonged period of time. This therefore limits

the extent to which recommendations can be made on the use of CWFs as a long-term

solution to improving water quality. The consequence of having such few research papers on

sustainability together with the clear heterogeneity in results leaves no room for inference of

possible trends or identification of factors that affect sustainability. This study has therefore

found a lack of evidence that would help implementers and policy-makers identify key areas

to improve sustainability of CWF interventions.

24

Due to the lack of research of CWFs, search terms and inclusion criteria were kept relatively

broad so as to incorporate more papers. However this has led to more biases and

inconsistencies in results as well as limiting our understanding of factors affecting

sustainability. There may be more information from NGO reports which would have been more

useful in terms of understanding the pitfalls and successes of a sustainable intervention.

However, some reports were unavailable to public domain and the lack of standardised

methodology could have opened the door to more biased results, particularly given that NGOs

are more likely to overestimate the effectiveness of their intervention.

Reasons for such a lack of research is likely due to the challenges faced when assessing

effectiveness and sustainability. All of the research that looked at health outcomes of CWF

used an RCT design whilst cross-sectional surveys were the most accurate for assessing

factors associated with long-term use. Whilst RCTs are seen as the gold standard for

determining intervention effectiveness, designing an RCT to assess sustainability may be too

unrealistic given that few outcomes, such as filter longevity or accessibility, in the control group

cannot be measured. This leads onto the second problem of deciding when the ideal time

point for assessing sustainability would be. Results of this review shows that the longest time

since distribution of filters was 4 years before a cross-sectional survey producing a high quality

paper(26). The other cross-sectional surveys were conducted 9 months-2 years post

implementation. There appears to be a clear lack of research over a prolonged period of time

which is a core requirement for assessing whether an intervention is maintainable.

In order to first assess whether CWFs are a sustainable intervention, it is important to

investigate whether the filters can consistently provide safe water. WHO guidelines on water

quality state that there should be no detectable level of harmful pathogen in drinking water(35)

and, in order to achieve this, CWFs must therefore be 100% effective at removing microbes.

Research in labs have shown that CWFs can perform to a high level(36) although whether the

same efficacy is translated in the field has been debated. For example, studies have found

46/79 filters had a negative log10 reduction value of E. coli demonstrating a higher

concentration of bacteria in the treated water than untreated water(37). A similar study, where

17% of effluent water samples had higher concentration of E. coli than influent water, drew

attention to a possible regrowth of bacteria on the tap of the receptacle(23). These findings

clearly point out how easily recontamination of water can occur in the home. Given that some

filter designs such as the siphon filter will deposit treated water into an open bucket, exposing

the treated water to flies or contaminated fingers when collecting water, this highlights how

filters with a 99% microbial removal in the lab does not necessarily mean clean and safe water

is being consumed by the user.

25

Although delivery of safe water is important, the real question remains as to whether CWFs

are effective at reducing diarrhoeal disease. Results provided were diverse with no definitive

answer. Such a heterogeneity of results in effectiveness can be accounted for by a number of

factors such as the importance of different waterborne pathogens in each setting, compliance

of participants or implementation approach. Many of the RCT go into detail about methodology

of assessing filter effectiveness although few have detailed the approach used when

distributing the filters. None have specified what information recipients received or specifically

stated that an inspection was made to ensure all participants in the intervention arm actually

received the filter. Disregarding this aspect can lead to a type 3 error; a phenomenon of a

phantom intervention where an estimate of effect may not actually be measuring any

intervention. In order to counteract this problem, recognising fidelity and compliance would

strengthen the reliability of the study. Fidelity is defined as how well an intervention is

implemented in comparison to the original procedure design. All of the papers either failed to

complete this or failed to reference this is in their methodology. Only one out of the four studies

that measured diarrhoeal disease incidence measured compliance(25) although the other

three tested water quality during visits therefore inadvertently ensured filters were in use(29,

31, 32). Future research should explicitly state the method of assuring fidelity and compliance

in order to strengthen the statistical power of outcome measurements.

Randomised controlled trials, seen as the gold standard for evaluating the effectiveness of an

intervention, was used for all four papers. One of the major concerns when conducting RCTs

of household water treatment is the lack of blinding leading to observer and participant bias.

Producing a placebo filter is simply unfeasible given that the design of the placebo would need

to replicate filtering of turbid water to clear water without compromising the microbial content

of the effluent water. In addition, there are significant ethical concerns since households may

cease their current water treatment to use the control placebo filter putting people at high risk

of drinking contaminated water leading to more incidence of diarrhoea. Communities in the

control group may also lose trust in interventions and NGOs. As such, no blinded RCTs have

been conducted on the effectiveness of CWFs. Implications of an unblinded intervention trial

may lead to control groups over-exaggerating diarrhoeal episodes to secure a filter for the

household and intervention arm under-reporting incidence of diarrhoea to please the

investigators(38). This unblinded approach can cause type I error; detecting an effect that is

not present. A ratio of odds ratio was calculated for lack of blindness in intervention trials giving

a value of 0.75 (0.61-0.81) demonstrating that all non-blinded RCT effect sizes would need to

be multiplied by 0.75 in order to correct for blinding(39). Indeed, when adjusting for blindness

26

in meta-regression of HWT interventions, the relative risk increased from 0.56 (0.51-0.63) to

0.85 (0.76-0.96) making the size of effect much smaller and the upper limit of the confidence

interval close to the value of no effect of 1(40). With such low conclusive evidence, it is

believed that the effects of HWT intervention may be entirely explained by bias either from

lack of blinding or through publication bias(41).

For all of the studies reviewed, health was a subjective outcome measured through incidence

of diarrhoeal episodes. In three of the studies, data was collected during visits that relied on

memory of episodes in the past week increasing the chances of recall bias. It is considered

this method is inaccurate beyond 48 hours, particularly given that the respondent would need

to account for other family members such as those under 5(42). Only in du Preez’s paper is a

different and possibly more accurate method used with a pictorial diary whereby recall of

diarrhoea disease was only required for the past 24 hours(32). However respondents may not

truthfully report diarrhoeal disease episodes for a number of reasons; embarrassment, fear of

the investigator or misunderstanding of the definition of diarrhoea are just three examples.

Since blinding is not possible, this unreliability of recall is likely to occur non-randomly between

the control and intervention arm and can overestimate the intervention’s effectiveness(43).

It is important for RCTs to specific whether intention-to-treat (ITT) or per protocol was used

for analysing the difference between control and intervention arm. Using ITT, whereby the

groups are analysed according to their original allocation, reduces the chance of bias since

the process of randomisation should, in theory, produce groups that have similar

characteristics apart from the intervention(44). On the other hand, per-protocol is analysing

the differences according to which individuals are in fact using the filter, that is to say are

complying, and resulting bias as the differences between intervention and control are due to

human behaviour traits. Only one RCT measured compliance throughout the trial however

none of the papers specifically stated which of ITT or per-protocol was used.

Although research on effectiveness of CWF has produced heterogeneous results, there is a

promising, albeit rather weak, association between reduction in diarrhoea and use of CWFs.

However, the potential impact of CWFs is limited given the fact that improving drinking water

quality only prevents one transmission route of the faecal-oral pathway (see figure 2) and only

addresses the waterborne agents of water-related diseases (see table 1). However it is

believed that the transmission of pathogens from fluids to new host is a major pathway in low-

resource settings with high endemicity of diarrhoea and so treating water at the household

level is more effective at reducing diarrhoea than other WASH interventions, particularly in

comparison to water quality interventions at the source since risk of recontamination during

transport and storage is high(15, 17). As well as CWFs directly preventing ECD, it can hinder

27

the vicious malnutrition diarrhoea cycle and as such could potentially indirectly prevent early

childhood mortality.

Of course, none of these possible health outcomes are possible without compliance by the

user. To highlight its importance, modelling of CWF sustainability found compliance to be a

main driving factor affecting outcomes such as ECD(45). Indeed research has found that the

benefits of increasing log10 reduction values of the filter are strongly dependent on

compliance(46). If compliance is low, there are diminishing returns from increasing LRVs

reducing the efficacy of the filter and reducing chances of beneficial health outcomes. This

review found no clear trends in compliance across the literature with a wide range of results

from 98% compliance over 18 weeks(25) to no compliance after 6 months(33). Since

measurement of compliance relied on self-reports of usage, this opened the door to courtesy

bias leading to an overestimation of usage as participants are more likely to over-report it’s

usage to please the investigator. Five papers had investigated bacteria count of effluent water

at the same time and, in this way, reduced the chances of users overstating its use since the

filter would have to be working at time of visit in order to take samples. Similarly, Brown et al.

and Casanova et al. specifically showed that checks were done in order to confirm the filter

was being regularly used(26);(27).

Such heterogeneous results in compliance can be accounted for by a number of different

factors. One of the most important distinctions that should be discussed is the difference in

settings. Three papers had carried out investigations in a post-disaster situation (Ensink 2015

was considered post-disaster) whilst the other four were part of standard development

interventions. It is believed that post-disaster circumstances would increase the uptake and

usage of filters due to increase in waterborne diseases, the loss of their usual trusted water

source or willingness to accept anything that should improve their current situation(47-49).

Contrastingly, user compliance in a development setting requires more challenging behaviour

and attitude change because households may already feel they have a trusted and safe water

source and there is not is such a high incentive to incorporate filtering into their daily lives. By

this logic, interventions post-disaster should have a higher compliance than development

interventions however the results have not followed this trend.

Understanding reasons for compliance and acceptance of CWFs by communities is extremely

complex and beyond the scope of this literature review. More studies, through surveys and

interviews, would begin to help identify what incentivises uptake and compliance of CWFs and

could help mould future implementation strategies since acceptance by community is central

to a successful WASH intervention with optimal health outcomes. However, given the fact that

28

results in prolonged filter use has not been consistent in this review, it does not make a strong

case for a sustainable intervention.

One of the main factors that can affect user compliance is the durability of the technology

itself. CWFs are usually made locally and, since there are no universal standards for filter

manufacturing, it is therefore difficult to ensure quality of each filter is to a high standard. This

review found that the most common reason for discontinuation of a filter was due to breakage

however there were no clear trends found most probably due to the variation in design,

porosity and manufacturing process of the filter. Differences in response to breakages were

diverse. For example, in Pakistan, tightening of the filter caused damage to the point where

filter could no longer be used(33) whereas, in Sri Lanka, households had reported cracking of

the ceramic vessel although worryingly continued to use it even though its efficacy in filtering

microbes would have decreased(27). The danger with this problem is that users are given a

false sense of security about the quality of water they are drinking and continue to use the

filter even though there may be no health benefits.

Ceramic water filters are expected to have a flow rate of 1-3L/hr which would provide adequate

supply of drinking water to a household. However, slow flow rate appeared to be a common

complaint across the literature with one study finding over half the filters’ flow rate below 1L/hr.

Even under laboratory conditions, the ceramic filter does not provide convincing evidence it is

a technology that can consistently perform. Research on filters from three different production

lines found all filters decreased flow rate to below 0.5L/hr after 12 weeks(50). Similarly, using

a continuous flow dosing system, filters did not reach their expected lifespan before physically

failing(51). Understandably, these results are not representative of filter performance in situ

and may even be underestimating filter durability since source water, particularly in low-

income settings may have a higher turbidity and therefore more likely to cause clogging thus

slowing the flow rate. Restoring flow rate can be achieved by scrubbing the filter although this

can weaken the integrity of the ceramic material consequently shortening the lifespan of the

filter(52). There appears to therefore be a compromise between slow filter rate and breakage

of the filter which does not make a strong case for an intervention with prolonged compliance

and consistent efficacy.

It appears that the filter technology, in addition to requiring regular replacement is relatively

prone to breakage therefore, in order to sustain the intervention, participants must be willing

to pay for a replacement or new filter. Methodology reviewed in the literature relied on open-

ended questions for a hypothetical price respondents would be willing without any justification

or consequence. This method is essentially biased since there is no incentive, such as actually

purchasing the filter with their answer, to be honest. Indeed, meta-analysis found an average

29

ratio of hypothetical to actual value of 2.6(53). Research in Northern Ghana on WTP for

ceramic filters found that the take-it-or-leave-it (TIOI) offer, whereby investigators ask if

participants are willing to buy at a set amount and have until the end of the day to pay for a

filter, found this method to be the most accurate compared to a similar open-ended question

methodology(54). Unfortunately mean WTP figures provided across the papers are non-

comparable given the fact there is economic variability between all study sites. In order to pool

results, a more accurate method may have been to present WTP as a proportion of their

weekly/monthly income or as a proportion of the market price. Mean WTP figures were

relatively low with some less than the market price. This is reflective of a systematic review

which found that, across WTP for household water treatment research, average WTP price

was consistently lower than market price suggesting a universal lack of demand for increased

water quality and not just for CWFs (55). Whether this trend is due to indifference towards the

filter or simply deficiency of personal funds has not been clarified in any of the studies

nevertheless it does not present a strong case for a sustainable intervention. Research

investigating WTP for water has also found that people are less willing to pay for water quality

and more on the time spent collecting the water(13). Since HWT does not reduce the time

spent collecting water, but in fact increases time spent on water duties, this may explain why

WTP for CWF or replacement parts is relatively low.

WTP is just one aspect of the process of replacing the filter component and heavily relies on

gaining access to replacements/spare parts, especially important since the majority of CWF

interventions occur in a rural setting. Although no research specifically looked at the role of

accessibility as a barrier for sustaining the intervention, the fact that up to 98% of study

participants did not know where to buy a filter from(27) in some studies and only 13% of regular

users had replaced the candle component(26) clearly demonstrates the high occurrence of

missed opportunities to buy a replacement. Even in interventions that made parts accessible

to the participants, a third of the filters were broken with no replacement demonstrating a

possible apathy continuing to use the filter(28). The studies, nevertheless highlight that it is

not necessarily lack of access to replacements that is a limiting factor but rather the lack of

awareness about location of supplier or knowledge of when to change the filter. More research

is needed that could successfully identify why replacement of filters is so low, recognising

major barriers and rectifying these problems for future interventions.

30

7.0 Conclusion/Recommendations

This literature review found a clear lack of evidence for ceramic water filter effectiveness and

sustainability. Even in studies that assessed the health impact of CWFs, bias due to lack of

blinding was an inherent trait and does not provide convincing evidence that would allow future

recommendations to be made. There certainly has been no research on the long-term health

impact of a CWF intervention. There is no doubt that improving water quality within the home

is beneficial, however the danger arises when water quality interventions are favoured over

water quantity or adequate sanitation. Implementing a CWF should only be seen as an

incremental step towards achieving prevention of all faecal-oral transmission routes and there

is concern that much needed resources may be diverted once a CWF intervention has been

put in place. In order to truly achieve significant health impact, an integrated approach of

improving water quantity, water quality and sanitation is required although in most low-income

settings this is simply too costly.

Examining the five main indicators of sustainability, a general theme across the studies was

the overall indifference towards to filter. Low compliance, low willingness-to-pay for a

replacement and a low proportion of successfully replaced filters indicates a possible apathy

towards the filter. More research on customer satisfaction would help understand whether

there is an actual demand for CWFs in the first place however, so far, the evidence does not

give a strong case for a sustainable intervention. Nevertheless in low-resource settings, HWT

interventions are the only solution and, in comparison to the other methods of treating water,

CWF does appear to be the most appropriate.

31

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