AWWA JAW56675

Although utilities strive to maintain water quality from the treatment plant, through the distribution system, and into customers' homes and businesses, at times microbial indicators are present but go undetected in treated water. This results in apparent contamination downstream in the distribution system. Causes of this contamination can be diminished by tracking and eliminating low-pressure events (including transitory ones), cross-connections, and inadequate disinfection procedures during distribution system maintenance. However, the complexity of distribution systems and the dispersion of related information, such as water quality, hydraulics, asset condition, and operation and maintenance, often prevent the causes of water quality failures from being identified. This lack of understanding of the origin of positive coliform samples leads to a nonactive approach as long as the problem is not acute with regard to public health or compliance issues. Key points to understanding and solving coliform existence in distribution system water include taking into account the hydraulics and daily operation and maintenance of storage tanks and pipe systems. The authors believe that analyzing coliform problems is the first step toward solving them, and they review the parameters involved in understanding and predicting these problems. They also make a strong case for replacing coliform testing with Escherichia coli-testing as a regulatory tool. Includes 151 references, tables, figures.