ing from distribution system contamination. The stakeholder and industry experts who attended the workshops agreed on the need to evaluate and prioritize potential health risk.

The approach to prioritization taken by the committee was based on a careful assessment of the issues presented in the nine white papers, critical evaluation of other materials, and on the committee’s assessment of the health importance of the various events. Given limited data on the specific causes of waterborne disease outbreaks, the best professional judgment of the committee was used to assess the magnitude of the health problem associated with an event, including how often the event occurs and how much contamination results when an event occurs. In addition to prioritizing the issues presented in the nine white papers, the committee also considered whether any significant issues had been overlooked by EPA when the white papers were written.

It should be noted that EPA had a difficult task in developing these white papers. A water distribution system is a complex engineering and ecological system wherein multiple adverse changes may result from the same or similar underlying causes. For example, water that has a long residence time in the system (high water age) may also have the potential to lose disinfectant residual and undergo biological nitrification. Considering any of these occurrences in the absence of the others oversimplifies the nature of the problem. However, the committee decided to follow the structure of the EPA white papers in preparing this report, with the recognition that overlaps and difficult-to-separate phenomena exist.

Of the issues presented in the nine white papers, cross connections and backflow, new or repaired water mains, and finished water storage facilities were judged by the committee to be of the highest importance based on their associated potential health risks. In addition, there are two other issues that should also be accorded high priority: premise plumbing and distribution system operator training.

CROSS CONNECTIONS AND BACKFLOW

Points in a plumbing system where non-potable water comes into contact with the potable water supply are called cross connections. A backflow event occurs when non-potable water flows into the drinking water supply through a cross connection, either because of low distribution system pressure (termed backsiphonage) or because of pressure on the non-potable water caused by pumpage or other factors (termed backpressure). Backflow incidents have long been recognized as significant contributors to waterborne disease. From 1981 to 1998, the CDC documented 57 waterborne outbreaks related to cross-connections, resulting in 9,734 detected and reported illnesses (Craun and Calderon, 2001). EPA compiled a total of 459 incidents resulting in 12,093 illnesses from backflow events from 1970 to 2001 (EPA, 2002b). For the period 1981 to 1998, EPA found that only 97 of 309 incidents were reported to public health authorities, demonstrating that the magnitude of the public health concern due to cross-connections is underreported. The situation may be of even greater concern because incidents involving domestic plumbing are even less recognized. In a study of 188 households, the University of Southern California’s Foundation for Cross-Connection Control and Hydraulic Research reported that



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