The Joint Monitoring Programme for Water Supply and Sanitation estimates that 1.1 billion people live without improved water sources, while over half of the developing world population, representing 2.6 billion people, lacks access to improved sanitation (WHO/UNICEF, 2004). Interventions aiming to improve water quality, water supply, sanitation and hygiene (WASH) have important social and economic benefits, with implications for environmental cleanliness, health, poverty reduction and (gender) equity. WASH interventions provides barriers to transmission from the environment to the human body of diarrhoeal disease, which is responsible for an estimated 21 per cent of fatalities of children under five years of age in developing countries, or 2.5 million deaths per year(Kosek et al., 2003). Interventions to effect improvements in WSH are therefore an important focus of efforts to improve the quality of life around the world. This review updates the existing systematic reviews and meta-evaluations in WSH, drawing on new evidence and rectifying methodological shortcomings.
To synthesise the effectiveness of WASH interventions in in promoting better health outcomes in developing countries as measured by the incidence of diarrhoea among children and to provide information relevant to programme planners, by collecting and analysing information on effectiveness, compliance and sustainability.
The authors included studies that employed rigorous impact evaluation techniques, using experimental (randomised assignment) and quasi-experimental methods (studies with baselines and concurrent control groups matched by confounding variables, and retrospective studies using propensity score matching).
The authors followed Campbell/Cochrane Collaboration standards for systematic reviews. They searched for published and unpublished literature, including among other databases PubMed and the Cochrane Library, the Web sites of organisations and search engines. The authors also included back-referencing and contacted subject experts for additional studies.
The authors present the results by intervention type in five categories: water supply improvements, water quality, sanitation, hygiene and multiple interventions involving a combination of water and sanitation and/or hygiene. They collected both quantitative and qualitative data for included studies, estimated effect sizes for each intervention and assessed the quality of the included studies. Finally, the authors used causal chain analysis and mixed methods to synthesise the results of the included studies. They carried out subgroup analysis and meta-regressions to assess the explanatory factors of intervention results.
The authors identified 65 high quality impact evaluations for quantitative synthesis, covering 71 distinct interventions assessed across 130,000 children in 35 developing countries during the past three decades. The authors find the following:
- Evidence on the combined impact of multiple interventions is mixed. Further primary studies comparing different interventions using multiple treatment arms in the same context are needed.
- Hygiene interventions, particularly the provision of soap for hand washing, appear to be effective in reducing diarrhoea morbidity. The analysis suggests that sanitation 'hardware' interventions are also highly effective, though the quality of the evidence base is far lower for these interventions. Studies are particularly needed that quantify the possible environmental spillovers from sanitation provision.
- Household water treatment interventions which aim improve quality of drinking water appear to be highly effective'indeed, more effective than water treatment at source in reducing diarrhoea. However, much of the evidence is from efficacy trials conducted among small populations and over short time periods. Water quality interventions conducted over longer periods tend to show smaller effectiveness, while compliance rates, and therefore impact, appear to fall markedly over time. More evidence is therefore needed on the sustainability of household water treatment interventions.
- Providing new sources of water to households and communities does not lead to benefits in terms of reducing diarrhoea among children on its own.
Overall, the study suggests the importance of behavioural factors in determining uptake and sustainable adoption of WASH interventions. Preventive interventions tend to be adopted more slowly, as benefits are difficult to observe.
The systematic review is based on a comprehensive search with clear inclusion criteria and use of mixed methods to analyse findings. However, the review has the following limitations. Two reviewers did not independently assess important information from included studies included effect sizes. In addition, given the range of quasi-experimental studies included, the methods used to assess risk of bias are not sufficiently transparent.