Data gathered by the Health Effects Research Laboratory, the U.S. Environmental Protection Agency, and the Center for Disease Control indicate that the major causes of waterborne disease outbreaks during 1971-1978 were contamination of distribution systems, deficiencies in treatment processes, and use of untreated, contaminated groundwater. Cross connection, backsiphonage, disinfection, phenol, polychlorinated biphenyl, coliforms, giardiasis are among the topics covered. Includes 22 references, tables, figures.