A randomized trial to evaluate the risk of gastrointestinal disease due to consumption of drinking water meeting current microbiological standards.

TLDR

The study aimed to quantify gastrointestinal illness associated with drinking tap water that meets current microbiological standards. A randomized trial assigned 299 households to receive reverse‑osmosis filters and 307 to continue using tap water, with GI symptoms recorded prospectively over 15 months. Filtered water reduced annual GI illness incidence from 0.76 to 0.50 (p < 0.01), indicating that about 35 % of tap‑water–related GI cases were preventable and suggesting current standards may be insufficient.

Abstract

BACKGROUND: This project directly and empirically measured the level of gastrointestinal (GI) illness related to the consumption of tapwater prepared from sewage-contaminated surface waters and meeting current water quality criteria. METHODS: A randomized intervention trial was carried out; 299 eligible households were supplied with domestic water filters (reverse-osmosis) that eliminate microbial and chemical contaminants from their water, and 307 households were left with their usual tapwater without a filter. The GI symptomatology was evaluated by means of a family health diary maintained prospectively by all study families over a 15-month period. RESULTS: The estimated annual incidence of GI illness was 0.76 among tapwater drinkers compared with 0.50 among filtered water drinkers (p less than 0.01). These findings were consistently observed in all population subgroups. CONCLUSION: It is estimated that 35% of the reported GI illnesses among the tapwater drinkers were water-related and preventable. Our results raise questions about the adequacy of current standards of drinking water quality to prevent water-borne endemic gastrointestinal illness.