Legionella are heterotrophic bacteria commonly living in natural waters. Our aim was to study occurrence of Legionella contamination in potable water supply systems in apartment and public buildings. Moreover, correlation between Legionella spp. positive cases and water source, sampling point and temperature of water, received at the point of consumption was studied. A total 250 water samples were collected from apartment and public buildings. Samples were taken in 21 cities and districts of Latvia. Only one Legionella species – Legionella pneumophila was isolated during this study. L.pneumophila was found in 72 out of 250 (29%) water samples. From all Legionella spp. positive samples, 19% represented L.pneumophila serogroup 1 and 78% L.pneumophila serogroup 2.-14.(15.). In 3% of Legionella spp. positive samples both serogroups 1 and 2.-14.(15.) where isolated. Statistically significant differences were observed in the distribution of L.pneumophila serogroup 1 in samples from various water sources in different districts. L.pneumophila was found in 32% of samples from private apartments and in 15% of samples from public buildings. Data analysis confirmed observation that temperature of hot water significantly affects the frequency of L.pneumophila positive cases (p<0.05).