You can read our discussion of the evidence supporting chlorine dispensers here, but in short:
- The Cochrane Review evaluated water interventions at point-of-use as well as more traditional water source improvements. The review covered 38 independent comparisons from 30 trials that involved more than 53,000 people. The review found that "in general, such interventions were effective in reducing episodes of diarrhea. Household interventions were more effective in preventing diarrhea than those at the source."
- A 3ie review covered 65 rigorous impact evaluations of water, sanitation and/or hygiene interventions on diarrhea morbidity, covering 71 distinct interventions assessed across 130,000 children in 35 developing countries during the past three decades. It concludes that point-of-use water quality interventions appear to be highly effective – and indeed, more effective than water supply or source treatment in reducing diarrhea – but that this is very sensitive to the ability of the program to sustain high rates of product adoption. A point of use product cannot provide health benefits if people do not use it.
- Researchers Arnold and Colford conducted a systematic review of all studies that measured diarrheal health impacts in children and the impact on water quality of point-of-use chlorine drinking water treatment. Twenty-one relevant studies were identified and combined using meta-analysis to provide summary estimates of the intervention effect. The intervention reduced the risk of child diarrhea by 29%, and up to 40% if you look at effects only among people actually using the product, as opposed to only being offered it.
There are shortcomings to the existing epidemiology literature. The reviews highlight the short duration of the studies that are available, and there is a need for more trials that are blinded or rely on objective measures of health outcomes instead of self-reported diarrhea.