The available data resources in the State of Iowa were used to investigate the relationships of drinking water contaminants and cancer incidence rates for communities. Age-adjusted, sex-specific cancer incidence rates for the years 1969-1978 were determined for municipalities having 1970 population of 1,000 or over and a public water supply that had remained stable for a minimum of 14 years. The cancer sites studied were bladder, lung, colon, rectum, stomach, prostate, and breast. These rates were examined according to major source of water supply (surface, deep or shallow ground), community size, time, and specific drinking water contaminants. These studies provide further indication that some drinking water contaminants such as radionuclides, chloroform, dibromachloromethane may be important in the etiology of some cancers.