More than 100 different enteric viruses are known to be excreted in human feces. More than 1 million viruses may be excreted per gram of feces, and concentrations as high as 500,000 infectious virus particles per liter have been detected in raw sewage. Certain enteric viruses can persist for long periods of time in the environment. Reported survival times range from 2 to 168 days in tapwater, 2 to 130 days in seawater, 25 to 125 days in soil, and up to 90 days in oysters. There are many potential routes of transmission back to man. An evaluation of the problems associated with viruses in water was prepared recently by the World Health Organization Scientific Group on Human Viruses in Water, Wastewater, and Soil which met in Geneva in October, 1978. Among its conclusions, four are pertinent to this article: (1) Viruses have been detected in the drinking water supply systems of a number of cities (including Paris and Moscow), despite the fact that those waters have received conventional water treatment considered adequate for protection against bacterial pathogens. (2) Conventional bacterial pollution indicators used to evaluate the safety of potable water supply have been shown to be significantly less resistant than viruses to environmental factors and water and waste‐water treatment processes. This leads to a situation where the more resistant enteric viruses can be present in water manifesting little or no signs of bacterial pollution. (3) Regular virus monitoring should be carried out to assure the freedom from enteric viruses in 100‐ to 1000‐/ samples in large urban centers where the water supply is derived from virus‐polluted surface water, a significant portion of which is untreated waste‐water or effluent insufficiently treated to inactivate viruses. (4) The constant exposure of large population groups to even relatively small numbers of enteric viruses in large volumes of water can lead to an endemic state of virus dissemination in the community which can and should be prevented.