For more than 100 years, U.S. public health personnel have relied extensively on an indicator organism approach to assess the microbiological quality of drinking water. These bacterial indicator microorganisms (particularly “coliforms,” described later) are typically used to detect the possible presence of microbial contamination of drinking water by human waste. More specifically, fecal indicator bacteria provide an estimation of the amount of feces, and indirectly, the presence and quantity of fecal pathogens in the water. Over the long history of their development and use, coliform test methods have been standardized, they are relatively easy and inexpensive to use, and enumeration of coliforms has proven to be a useful method for assessing sewage contamination of drinking water. In conjunction with chlorination to reduce coliform levels, this practice has led to a dramatic decrease in waterborne diseases such as cholera and typhoid fever. Furthermore, the use of bacterial indicators has been extended to U.S. “ambient” waters in recent decades—especially freshwater and marine-estuarine waters used for recreation. However, an increased understanding of the diversity of waterborne pathogens, their sources, physiology, and ecology has resulted in a growing understanding that the current indicator approach may not be as universally protective as was once thought. In this regard, several limitations of bacterial indicators for waterborne pathogens have been reported and are discussed throughout this report.

To protect public health, it is important to have accurate, reliable, and scientifically defensible methods for determining when water is contaminated by pathogens and to what extent. Furthermore, recent and forecasted advances in microbiology, biology, and analytical chemistry make it timely to assess the current paradigm of relying predominantly or exclusively on traditional bacterial indicators for waterborne pathogens in order to make judgments concerning the microbiological quality of water to be used for recreation or as a source for drinking water supply.

Committee and Report

This report was prepared by the National Research Council (NRC) Committee on Indicators for Waterborne Pathogens—jointly overseen by the NRC’s Board on Life Sciences and Water Science and Technology Board. The committee consists of 12 volunteer experts in microbiology, waterborne pathogens (bacteriology, virology, parasitology), aquatic microbial ecology, microbial risk assessment, water quality standards and regulations, environmental engineering, biochemistry and molecular biology, detection methods, and epidemiology and public health. The report’s conclusions and recommendations are based on a review of relevant technical literature, information gathered at four committee meetings, a public workshop on indicators for waterborne pathogens (held on September 4, 2002), and the collective expertise of committee members.

The committee was formed in early 2002 at the request of the U.S. Environ-

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