This paper summarizes the findings and conclusions of an 18-month study of water quality problems and alternative approaches to wastewater management in Contra Costa County, California. The Contra Costa County Water Quality Study was the first of a series of six subregional studies of its type to be undertaken in the San Francisco Bay area. The Contra Costa study was financially supported by the Contra Costa County Water Agency and by the federal government and the State of California acting through the State Water Resources Control Board. Financial support was also provided by the Western Oil and Gas Association in recognition of the importance of industrial wastes in the overall water quality management problems of the subregion.