Association between haloacetic acid degradation and heterotrophic bacteria in water distribution systems.

The occurrences of trihalomethanes (THMs), haloacetic acids (HAAs) and heterotrophic bacteria were monitored in five small water systems over a nine-month period to investigate the association between HAA degradation and heterotrophic bacteria populations. The sampling sites were chosen to cover the entire distribution network for each system. An inverse association between heterotrophic bacteria and HAA concentrations was found at some locations where chlorine residuals were around or less than 0.3mgL(-1). At other sample locations, where chlorine residuals were higher (over 0.7mgL(-1)), no HAA reduction was observed. A high heterotrophic bacteria count accompanied with a low chlorine residual could be used as an indicator for HAA degradation in distribution systems.