Warm and cold water as well as water from wash basin drains and faucet aerators was examined to determine the number of viable and dead bacteria by culture and by staining and to establish the spectrum of species with special consideration of Legionella pneumophila. The relation between the number of Legionella pneumophila, the temperature, and the iron content of the water was determined in three separate warm water systems. High colony counts (up to 8.9 X 10(5) colony-forming units), were detected in both warm and cold water at certain sampling sites. The most prevalent genera were Pseudomonas, Bacillus, Flavobacterium, Acinetobacter, and Moraxella. Legionella pneumophila was found in every building in 35 of 150 warm samples and in 1 of 43 cold water samples. The highest water temperature of a sample containing Legionella pneumophila was 64 degrees C. The correlation between high colony counts and the occurrence of Legionella pneumophila in the samples was not significant. High iron concentrations, however, appear to have a positive effect on the growth of Legionella pneumophila.