Evaluation of Field Testing Techniques Used in a Household Water Treatment Study in Posoltega, Nicaragua

A field evaluation of biosand filters, a method of household water treatment, was conducted in Posoltega, Nicaragua. The evaluation consisted of water quality testing for Escherichia coli and total coliforms using membrane filtration (MF) with m-coliBlue24 growth media, and SolarCult dipslides. For each sample tested, the MF procedure was applied to two volumes differing by an order of magnitude to capture the expected range of microbial contamination. A follow-up laboratory quality assurance/quality control procedure was undertaken to validate the field methods. The average coefficient of variation was 51%, with no statistically significant difference between the field and laboratory data. The MF procedure used with m-coliBlue24 produced useful reproducible results for the microbial concentrations encountered in the field. Dipslide results were found to correlate poorly to the membrane filtration results from the field, and should not be used to test drinking water due to the high limit of detection. They may still be useful for preliminary testing of highly contaminated source water as part of a household water treatment project. Dipslides may also be a useful tool for local health representatives to promote safe water practices within the community since they are simple to use and provide a visual indicator of water quality.