This slide presentation outlines information on the occurrence of legionellae in groundwater. Study objectives include: determine prevalence of legionellae in source waters and production wells [PW]; determine how widespread legionellae are in groundwater; assess importance of temperature and other water quality parameters in predicting occurrence of legionellae; and, investigate immunomagnetic separation [IMS] as a tool to isolate legionellae. Topics covered include: testing and location of samples; PCU source characteristics; culture methodology; confirmation and identification; results of legionellae culture; legionella species identified in PCU production wells during 1-year study; PCR methodology; results of PCR for legionellae; differences in means of selected parameters that are positive versus negative for legionellae; and, overall prevalence of legionellae in groundwater.