Interventions to improve water quality for preventing diarrhoea: systematic review and meta-analysis

BMJ 2007; 334 doi: (Published 12 April 2007) Cite this as: BMJ 2007;334:782
  1. Thomas Clasen, lecturer1,
  2. Wolf-Peter Schmidt, clinical research fellow1,
  3. Tamer Rabie, public health specialist3,
  4. Ian Roberts, professor of epidemiology2,
  5. Sandy Cairncross, professor of environmental health1
  1. 1Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT
  2. 2Department of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine
  3. 3World Bank, Washington, DC, USA
  1. Correspondence to: T Clasen thomas.clasen{at}
  • Accepted 4 January 2007


Objective To assess the effectiveness of interventions to improve the microbial quality of drinking water for preventing diarrhoea.

Design Systematic review.

Data sources Cochrane Infectious Diseases Group's trials register, CENTRAL, Medline, Embase, LILACS; hand searching; and correspondence with experts and relevant organisations.

Study selection Randomised and quasirandomised controlled trials of interventions to improve the microbial quality of drinking water for preventing diarrhoea in adults and in children in settings with endemic disease.

Data extraction Allocation concealment, blinding, losses to follow-up, type of intervention, outcome measures, and measures of effect. Pooled effect estimates were calculated within the appropriate subgroups.

Data synthesis 33 reports from 21 countries documenting 42 comparisons were included. Variations in design, setting, and type and point of intervention, and variations in defining, assessing, calculating, and reporting outcomes limited the comparability of study results and pooling of results by meta-analysis. In general, interventions to improve the microbial quality of drinking water are effective in preventing diarrhoea. Effectiveness was not conditioned on the presence of improved water supplies or sanitation in the study setting and was not enhanced by combining the intervention with instructions on basic hygiene, a water storage vessel, or improved sanitation or water supplies—other common environmental interventions intended to prevent diarrhoea.

Conclusion Interventions to improve water quality are generally effective for preventing diarrhoea in all ages and in under 5s. Significant heterogeneity among the trials suggests that the level of effectiveness may depend on a variety of conditions that research to date cannot fully explain.


  • We thank Greg Allgood, Jamie Bartram, Julia Bohlius, Joseph Brown, Jack Colford, John Crump, Tom Chiller, Val Curtis, Shannon Doocy, Lorna Fewtrell, Carrol Gamble, Bruce Gordon, Stephen Gundry, Bruce Keswick, Steve Luby, Rob Quick, Mark Sobsey, Sara Thomas, and James Wright for their research, advice, assistance, and other valuable contributions; members of the Cochrane Infectious Diseases Review Group; and the referees of the Cochrane review and its protocol.

  • Contributors: SC conceived the review. TC coordinated the review, drafted the protocol and review, carried out the search strategy, retrieved the papers, contacted authors, and prepared the tables and figures. TC is guarantor. TC, IR, TR, and W-PS designed the review. TC and TR screened the search results. TC, TR, and SC applied the inclusion criteria. TC, TR, and W-PS extracted the data, calculated estimates of effect, and dealt with the statistics. TC, TR, and IR applied the quality criteria. TC and W-PS entered data into RevMan. IR, TR, W-PS, and SC commented on the review.

  • Funding: None.

  • Competing interests: TC, W-PS, and SC participate in research supported by Unilever and Vestergaard-Frandsen, which manufacture and sell household or other point of use water treatment devices.

  • Ethical approval: Not required.

  • Accepted 4 January 2007
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