An investigation of Legionella pneumophila in drinking water systems and home plumbing appurtenances was done. In Phase 1, 68 water samples were collected from kitchen sink faucets in homes on 17 community water systems. No. L. pneumophila organisms were isolated. In Phase 1A, the kitchen sink faucets/aerators and showerheads/supply pipes were sampled with sterile swabs and a sample of hot water was collected from hot water heaters. A total of 92 swabs, 92 hot water samples were collected from homes on 4 community water systems. Two samples (1 swab, 1 hot water sample) were collected from a home with an individual well. Field analyses of pH, temperature, turbidity, and chlorine and laboratory analyses for standard plate count, total coliform, and iron were performed. Findings may indicate that L. pneumophila is transported from natural aquatic sources in very low levels in drinking water systems to water heaters in homes where the organisms may increase to detectable levels. These sources may serve as a focus of the pathogen with resultant sporadic, endemic legionellosis.