Paul Hunter, Professor of Health Protection with the School of Medicine, has examined previous studies of the effectiveness of household water treatment (HWT) systems and has concluded many of these studies are too short-term to provide conclusive evidence that systems actually work. Professor Hunter also identified significant short-comings in study design which further undermines these reports.

Many of these HWT systems are designed to work either by disinfecting the water using chlorine, by allowing the ultraviolet radiation in sunlight to purify stored water, or by passing it through ceramic or sand filters. The research indicates that in many cases the effectiveness of these systems at reducing diarrhoea have been over stated and the evidence to support their effectiveness flawed.

Professor Hunter said, "A lack of blinding biases the results by up to about 30 per cent and when you account for this bias and also the decline in effectiveness with time, many of the HWT technologies appear to have little if any health benefit over the long term. The big exception are the ceramic filters which have a substantial and sustained impact on reducing diarrhoeal disease.” He continued, “Before HWT or indeed any public health programmes are rolled out in developing country settings they should be subject to much more rigorous testing as would be expected for new drugs."