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Titanium dioxide in the anatase crystalline form was used as a photocatalyst to generate hydroxyl radicals in a flowthrough water reactor. Experiments were performed on pure cultures of Escherichia coli in dechlorinated tap water and a surface water sample to evaluate the disinfection capabilities of the reactor. In water devoid of significant amounts of inorganic-radical scavengers, rapid cell death was observed with both pure cultures and members of the indigenous flora in a natural water sample.

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OBJECTIVES: A 1993 large water-borne outbreak of Salmonella typhimurium infections in Gideon, Mo, a city of 1100 with an unchlorinated community water supply, was investigated to determine the source of contamination and the effectiveness of an order to boil water. METHODS: A survey of household members in Gideon and the surrounding township produced information on diarrheal illness, water consumption, and compliance with the boil water order. RESULTS: More than 650 persons were ill; 15 were hospitalized, and 7 died. Persons consuming city water were more likely to be ill (relative risk [RR] = 9.1, 95% confidence interval [CI] = 2.9, 28.4), and the attack rate increased with increased water consumption. S. typhimurium was recovered from samples taken from a city fire hydrant and a water storage tower. Persons in 31% (30/ 98) of city households had drunk unboiled water after being informed about the boil water order, including 14 individuals who subsequently became ill. Reasons for noncompliance included "not remembering" (44%) and "disbelieving" (25%) the order. CONCLUSIONS: Communities with deteriorating water systems risk widespread illness unless water supplies are properly operated and maintained. Effective education to improve compliance during boil water orders is needed.

Models of chlorine kinetics in distribution systems characterize chlorine decay as a combination of first‐order decay in the bulk liquid and first‐order or zero‐order decay reactions at the pipe wall. Proper understanding, characterization, and prediction of water quality behavior in drinking water distribution systems are critical to ensure meeting regulatory requirements and customer‐oriented expectations. This article investigates the factors leading to loss of chlorine residual in water distribution systems. Kinetic rate equations describing the decay of chlorine were developed, tested, and evaluated using data collected in field‐sampling studies conducted at several water utility sites. Results indicated that chlorine decay in distribution systems can be characterized as a combination of first‐order reactions in the bulk liquid and first‐order or zero‐order mass transfer–limited reactions at the pipe wall. Wall reaction kinetic constants were inversely proportional to pipe roughness coefficients. Wide variations in both bulk reaction constants and wall reaction constants were observed among the sites.