Limiting Standards of Bacterial Quality for Sources of Purified Water Supplies

Abstract

The growing difficulties experienced in obtaining purified water supplies of safe and palatable quality from sources highly polluted by sewage and industrial wastes have made apparent the need of applying some rational standard whereby excessive pollution of these sources can be brought under some definite and economical control. In several states, a tentative standard of this kind has been adopted, based on the results of a comprehensive study of the limitations of current water purification processes made a few years ago by the U. S. Public Health Service in connection with its investigations of stream pollution. Although the results of this study have been fully published elsewhere, it has seemed desirable to undertake in this paper an interpretation of them with particular reference to the formulation of a working standard such as above indicated and to illustrate its application in one or two specific cases. In connection with the Public Health Service's study, three major series of observations were made. The first consisted of a detailed collective survey of the performance of 17 representative municipal water purification plants located on the Ohio and several other rivers; the second, of a similar survey of 14 plants located along the Great Lakes; and the third, of a long series of observations, aggregating some five years in time, at a large-scale experimental water filtration plant located on the Ohio River at Cincinnati. Although the combined data of this study embraced almost every conceivable combination of water treatment, ranging from simple chlorination to highly elaborated filtration, with double-stage coagulation, sedimentation and chlorination, the process most frequently observed was ordinary rapid-sand filtration, aided by post-chlorination. As this particular combination of treatment appears to represent the normal type used most widely throughout the United States, its performance represents probably the most reasonable basis of any general requirements which might be adopted for limiting raw water pollution.