Legionellae are found in freshwater environments or wet soil, but the major reservoirs are man-made aquatic environments, particularly warm water systems. Our aim was to study the occurrence of Legionella contamination in hot potable water supply systems in apartment and public buildings. Correlations between Legionella spp. positive cases and water source, sampling point and temperature of hot water at the point of consumption were studied. A total of 149 hot water samples were collected in 16 cities and districts of Latvia. Only Legionella pneumophila was isolated. L. pneumophila was found in 63 out of 149 (42%) hot water samples. From all Legionella spp. positive samples, 17% represented L. pneumophila serogroup 1 and 78% L. pneumophila serogroups 2-14 (15). In 5% of Legionella spp. positive samples, both serogroups 1 and 2-14(15) were isolated. Statistically significant differences were observed in the distribution of L. pneumophila serogroup 1 in samples from various water sources. L. pneumophila was found in 45% of samples from private apartments and in 27% of samples from public buildings. Data analysis confirmed that the temperature of hot water significantly affects the frequency of L. pneumophila positive cases (p < 0.05). Data showed that 85% of consumers received hot water at a temperature below 50 °C.