NAS Report Addresses Deteriorating U.S. Water Distribution Systems

Sep 7: Much of the 1 million miles of pipes that make up U.S. water distribution systems are nearing the end of their expected life span, and an increasing proportion of waterborne disease outbreaks are linked to contamination of distribution systems, according to a new National Academy of Sciences (NAS), National Research Council (NRC) report -- Drinking Water Distribution Systems: Assessing and Reducing Risks. The report addresses the challenges of protecting and maintaining water distributions systems, crucial to ensuring high quality drinking water. Distribution systems -- consisting of pipes, pumps, valves, storage tanks, reservoirs, meters, fittings, and other hydraulic appurtenances -- carry drinking water from a centralized treatment plant or well supplies to consumers taps. The 1 million miles in the U.S. water distribution systems represent the vast majority of physical infrastructure for water supplies, and thus constitute the primary management challenge from both an operational and public health standpoint. Recent data on waterborne disease outbreaks suggest that distribution systems remain a source of contamination that has yet to be fully addressed.

The issues and concerns surrounding the nation's public water supply distribution systems are many. Of the 34 billion gallons of water produced daily by public water systems in the United States, approximately 63 percent is used by residential customers. More than 80 percent of the water supplied to residences is used for activities other than human consumption such as sanitary service and landscape irrigation. Nonetheless, distribution systems are designed and operated to provide water of a quality acceptable for human consumption. The type and age of the pipes that make up water distribution systems range from castiron pipes installed during the late 19th century to ductile iron pipe and finally to plastic pipes introduced in the 1970s and beyond. Most water systems and distribution pipes will be reaching the end of their expected life spans in the next 30 years (although actual life spans may be longer depending on utility practices and local conditions). Thus, the water industry is entering an era where it will have to make substantial investments in pipe assessment, repair, and replacement.

The report evaluates approaches for risk characterization and recent data, and identifies a variety of strategies that could be considered to reduce the risks posed by water-quality deteriorating events in distribution systems. Particular attention is given to backflow events via cross-connections, the potential for contamination of the distribution system during construction and repair activities, maintenance of storage facilities, and the role of premise plumbing in public health risk. The report also identifies advances in detection, monitoring and modeling, analytical methods, and research and development opportunities that will enable the water supply industry to further reduce risks associated with drinking water distribution systems. The report proposes that U.S. EPA work with states to establish consistent cross-connection control programs and to improve and unify plumbing codes, among other recommendations. An initial report entitled, Public Water Supply Distribution Systems: Assessing and Reducing Risks, First Report, is included as an appendix to the final report.

Access a 27-page Executive Summary of the report (click here). Access the complete 437-page report on-line by chapters (click here). [*Drink]