The results of a study of the level of Legionella contamination in the water systems of the Metropolitan metropolis are presented. The study of biological contamination of Legionella pneumophila in water bodies of Moscow (Central administrative district) for social purposes (swimming pools, Jacuzzi, boiler room, fountain, and cooling water for cooling towers) revealed the occurrence of the studied species from 7% to 20%. The most frequent occurrence of Legionella pneumophila was found in the Central water supply of the city (CAO of Moscow), which was 36%. For the control and reduction of the activity of pathogens as Legionella pneumophila in water systems of public facilities the city needs to monitor the temperature changes in water supply in the building (hot water should be at a temperature higher than 60 °C and cold below 20 °C). It is also important to use the filters in the taps and showers and to carry out the ionization of water.