The following section provides an executive summary of this paper, highlighting the key findings in relation to the priority areas identified by DFID. The paper sets out the methods for this review and the approach for assessing the strength of evidence. The different bodies of evidence reviewed in this paper have been graded as ‘good’, ‘suggestive, and ‘weak’ as per the criteria below:
• Good evidence: several good quality studies that consistently show an effect. For example, randomised trials with a low risk of bias or observational studies showing a large effect size with a low potential for confounding
•Suggestive evidence: studies which show an effect but statistical support is weak due to insufficient study size. Or, studies which show significant effects but there is a risk of bias and confounding
•Weak evidence: no studies have been done or, where they been done, they have shown inconclusive results.

A summary assessment of the evidence underlying the impact of the four main Water, Sanitation and
Hygiene (WASH) interventions on diarrhoea according to seven ‘points of view’ is also scored as ‘favourable’, ‘intermediate’ and ‘unfavourable’. This shows the degree to which, from each viewpoint, the available evidence supports or undermines the case for implementation of each intervention. The scoring given for each cell of the table reflects the individual gradings given for the strength of evidence throughout this paper.