The article is devoted to the study of bacteria in the system of technical water supply of Balakovo nuclear power plant (BNPP). The work was carried out in 2017. The samples were taken at the following sites: backup diesel generator of the 3rd unit (rode’s-3), pumping station of feeding pond-cooler (PSFPC), coastal pump station of unit 3 (CPS-U3), coastal pumping station of power unit № 4 (CPSP-U4), turbine hall of power unit № 3 (TH-PU3), turbine hall of power unit № 4 (TH-PU4).