SUMMARY Public health protection requires an indicator of fecal pollution. It is not necessary to analyse drinking water for all pathogens. Escherichia coli is found in all mammal faeces at concentrations of 10 log 9−1, but it does not multiply appreciably in the environment. In the 1890s, it was chosen as the biological indicator of water treatment safety. Because of method deficiencies, E. coli surrogates such as the ‘fecal coliform’ and total coliforms tests were developed and became part of drinking water regulations. With the advent of the Defined Substrate Technology in the late 1980s, it became possible to analyse drinking water directly for E. coli (and, simultaneously, total coliforms) inexpensively and simply. Accordingly, E. coli was re‐inserted in the drinking water regulations. E. coli survives in drinking water for between 4 and 12 weeks, depending on environmental conditions (temperature, microflora, etc.). Bacteria and viruses are approximately equally oxidant‐sensitive, but parasites are less so. Under the conditions in distribution systems, E. coli will be much more long‐lived. Therefore, under most circumstances it is possible to design a monitoring program that permits public health protection at a modest cost. Drinking water regulations currently require infrequent monitoring which may not adequately detect intermittent contamination events; however, it is cost‐effective to markedly increase testing with E. coli to better protect the public's health. Comparison with other practical candidate fecal indicators shows that E. coli is far superior overall.

A community waterborne nonbacterial gastroenteritis outbreak occurred in Eagle-Vail, Colorado in March 1981. Illness (defined as vomiting and/or diarrhea) was statistically associated with water consumption (X2 for linear trend = 7.07, p < .005). Five

The Colorado Department of Health conducted intensive surveillance for waterborne diseases during the three-year period July

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In November 1981, a waterborne giardiasis outbreak occurred within the Highlands Water and Sanitation District in Colorado. Although the immediate cause of the outbreak was reduced chlorine contact time because of a pump failure, numerous design and operational deficiencies existed at the plant. Lack of chemical pretreatment, improper backwashing procedures, poor application of raw water to the filter, and failure to monitor plant conditions all contributed to the outbreak. Turbidity and bacteriological records did not indicate any problems, confirming the crucial role of proper design, installation, and operation of the multibarrier technique in preventing waterborne giardiasis outbreaks. Giardiasis is an intestinal disease most