Footnotes

• Contributors All authors wrote and reviewed the paper, JHJE acts as guarantor of the content.

• Funding SC's and JHJE's time was funded by the DFID research programme consortium on Sanitation and Hygiene (SHARE: grant no. P04990).

• Competing interests None.

• Provenance and peer review Commissioned; externally peer reviewed.

• ↵i Although we do cite pooled estimates of effect for WSH interventions on child health from a number of systematic reviews, readers should note that there is a rich emerging literature that attempts comparisons of impact between water supply, water quality, hygiene and sanitation; Waddington et al 2009 provides a good summary that is still current. WSH interventions are not very amenable to randomisation (in the case of infrastructure) and are almost never blinded in trials, with the exception of a minority of water quality intervention trials. Therefore, randomised, controlled trials (RCTs) may be subject to significant bias, and RCTs constitute the majority of studies included in systematic reviews of WSH interventions. We cite these reviews where appropriate as important but potentially flawed estimates that may be considered suggestive only. A broader perspective on the evidence base may be more helpful.