Assessment of biosand filter performance in rural communities in southern coastal Nicaragua: an evaluation of 199 households

Abstract

Lack of access to safe drinking water is a major health issue for more than one billion people globally. In areas where community-wide water treatment is not possible, point-of-use (POU) solutions are necessary. The biosand filter (BSF) is one of several such POU technologies available to treat water in the home to reduce the risk of infection. This study was conducted to evaluate the use and performance of BSFs in the rural communities surrounding San Juan del Sur, Nicaragua. Approximately 600 filters had been installed in this area over the preceding 2 years by local workers supported by US and Canadian NGOs. This field study was conducted In July and August 2009. Unannounced household visits were carried out by US volunteers supported by a local interpreter and driver. Visits were made to a convenience sample of 199 households where BSFs had been in place for an average of 12 months. Water for analysis was collected from wells, filter spouts and storage buckets and an 11 item questionnaire was administered. Laboratory analyses were performed on water samples using the membrane filtration method to determine Escherichia coli colony forming units (CFUs). Forty-five of 199 households visited had discontinued use of their BSF. In the 154 households tested, median CFU of E. coli per 100 mL of water from the source, filter spout and storage vessel were 313, 72, and 144, respectively. Median bacterial removal efficiency for the filters was 80%. Although biosand filtration reduced CFUs in 74% of households in which it was used, in only 26 cases (17%) did it reduce CFUs to <10 CFUs/100 mL. Recontamination was an important problem and reduced the overall efficacy (from well to storage bucket) to 48%. Participants were generally satisfied with their filter's performance, citing improved health and better tasting water. Water quality testing of BSFs deployed in the field showed results somewhat inferior to previous reports. Possible explanations include lack of use of best practices and the inclusion of some filers in the analysis that may not have been in active use. Despite these results and high rates of recontamination in the storage bucket, most households members were pleased with their filters and claimed that their use had enhanced their health. This inconsistency could be due to inaccurate responses to the questionnaire for purposes of secondary gain.