Summarized data is presented on the maximum rainfall layer, runoff from which should be completely diverted to treatment facilities (runoff from residential areas and industrial enterprises of the first group in the Russian Federation). The calculated values of the precipitation layer are obtained from observations at 238 weather stations located in the Russian Federation, which are necessary for calculating the performance of surface water treatment plants. The results can be used in the design in areas for which these weather stations are representative. The size of the precipitation layer, which ensures the discharge of at least 70% of the annual volume of runoff to sewage treatment plants, for the territory of the Russian Federation is in the range of 2.2–12.8 mm.