The drinking water quality of 176 selected interstate carrier water supply sources is being determined in a joint program conducted in 1960-1963 by municipalities, State health departments and the Public Health Service. Samples of water are being analyzed for organic chemicals, radiochemicals and trace elements and other determinations generally classed as sanitary chemical analyses. Samples are composite over a two-week period and collected of finished water at points believed to be most representative of water consumed by residents of the community. The project consists of taking two series of samples, of which this publication gives data on the first.