The protection afforded the water consumer by the maintenance of a chlorine residual in water distribution systems was evaluated in laboratory holding tanks and reservoirs and existing municipal water distribution systems. In the laboratory studies, tap water, adjusted to the appropriate pH, temperature, and chlorine residual, was challenged with varying levels of autoclaved sewage seeded with Shigella, Salmonella coliforms, poliovirus 1, and f2 bacterial virus. Comparative survivals of these microorganisms were evaluated over two hour periods. As expected microbial inactivation was increased by lower pH, higher temperature, higher initial chlorine concentration, and lower sewage concentration. An initial free chlorine concentration was more effective than an equivalent initial combined chlorine residual. The maintenance of a free chlorine residual was found to be the single most effective measure for maintaining a low plate count in the distribution system. More than 6000 plate count isolates were studied and classified into functional groups based on seven biochemical characteristics.

Includes bibliographical references (pages 102-106). Prepared for U.S. Environmental Protection Agency, Office of Research and Development, Municipal Environmental Research Laboratory, Cincinnati, Ohio, submitted by the Johns Hopkins University, School of Hygiene and Public Health, Division of Environmental Health Engineering, under grant no. Contract Number: R804307.