The microbiological and health impact of the biosand filter in the Dominican Republic: a randomized controlled trial in Bonao

More than one billion people lack access to improved water supplies and even more lack access to safe water. Many household water treatment technologies have been documented to improve drinking water quality and reduce diarrheal disease. However, other technologies that are being used still lack rigorous evidence on ability to improve water quality and reduce diarrheal disease. One of these technologies is the biosand filter (BSF), an intermittently operated slow sand filter. It is estimated that more than 80,000 BSFs are in use world wide yet there is no rigorous evidence of their ability to reduce diarrheal disease and there is only limited evidence of their ability to improve drinking water. The purpose of this research was to examine the microbiological and health impact of the BSF in the laboratory and in the field. The laboratory research examined the ability of the BSF to reduce viruses and bacteria from water. The field research examined improvements in drinking water quality by the BSF in use in households and the ability of the BSF to reduce diarrheal disease. Based on the laboratory evidence, the BSF can achieve moderate to high reductions of bacteria 90-99% and moderate reductions of viruses (90%). The field study suggested moderate reductions of E. coli by the BSF in the field which was 80% on average yet it ranged 0-99.9%. The health impact portion of the field study found a 47% reduction in diarrheal disease in BSF users as compared to non-users. In addition, the health impact study found a weak association between increased contamination in drinking water as measured by E. coli and rates of diarrheal disease. The results from this research suggest that the biosand filter may be an effective way to improve drinking water quality and reduce diarrheal disease in the communities studied in Bonao, Dominican Republic.