Epidemiological studies in rural Mexico have shown the role of poor quality water in gastrointestinal disease incidence. This led to the establishment of a program, which included the assessment of inexpensive systems for household treatment of drinking water. We describe the main features of a hand carved stone filter evaluated over 6 months under laboratory conditions and 6 months under household conditions. The filter had a capacity of 5L and an average volume of 18L/d filtered water (the temperature of which was always an average 4°C lower than the influent). Average bacterial removals under laboratory conditions were 98% for total and faecal coliforms (TC, FC), 96% for faecal streptococci (FS), 99% for Pseudomonas aeruginosa and 100% for helminth eggs and protozoan cysts. During the field evaluation removals were 80–100% TC, 45–95% FC and 8–93% FS due to the different qualities of influent water and the operation conditions. Nevertheless, the filters represented an immediate mitigation measure of the health risks associated with the continuous ingestion of microbiologically unsafe waters.

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