lated to analytical methods for measuring water quality. Chapter 3 examines similar concerns related to microbial contaminants. Chapter 4 discusses methodological issues for conducting microbiological analysis, risk analysis, toxicological safety testing, and epidemiological studies. Chapter 5 reviews the health-related studies conducted by selected potable reuse projects. And Chapter 6 evaluates reliability and quality assurance issues for potable reuse projects.

Selection of Drinking Water Sources

Some public health authorities have been reluctant to allow or support the planned augmentation of water supplies with reclaimed municipal wastewater under any circumstances, subscribing to the maxim that only natural water derived from the most protected source should be used as a raw drinking water supply. This maxim has guided the selection of potable water supplies for more than 150 years. It was affirmed in the 1974 draft of the National Interim Primary Drinking Water Regulations, which states, "Production of water that poses no threat to the consumer's health depends on continuous protection. Because of human frailties associated with protection, priority should be given to selection of the purest source. Polluted sources should not be used unless other sources are economically unavailable" (U.S. EPA, 1975).

This principle was derived from earlier public health practices developed when understanding of drinking water contaminants was limited and when natural processes (such as dilution in rivers and natural filtration by soils), rather than technology, were relied upon to produce suitable drinking water. It is also derived from a time when the U.S. population was smaller, and our concern about protecting the environment from the impact of human-made impoundments less formalized, and when pristine water supplies were more available than they are today.

While a pristine drinking water source is still the ideal sought by most municipalities, the U.S. population has expanded, so that many large cities take water from sources that are exposed to sewage contamination. When these supplies were originally developed, the only health threats perceived were attributable to microbiological vectors of infectious disease. These vectors would be attenuated during flow in rivers and then easily eliminated with conventional water treatment processes such as coagulation, filtration, and disinfection. Such water supplies were generally less costly and more easily developed than higher quality upland supplies or underground sources. Today, however, most of these supply waters receive treated wastewaters from other communities upstream. Thus, cities such as Philadelphia, Cincinnati, and New Orleans, which draw water from the Delaware, Ohio, and Mississippi rivers, re-

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