The aim of the study is to analyze the hydraulic conditions of the existing sewage system and the sewage treatment plant in the commune of Mściwojów. This is in relation to the aspect of connecting new buildings, as a part of the investments in the pilot project VITAL LANDSCAPES no. 2CE164P3. The analysis led to the conclusion that an increased wastewater inflow from the new buildings is manageable. The current capacity of the sewage treatment plant will be increased by 3 to 5%, which will not affect the stability of the existing treatment process. The hydraulic analysis of the sewer network proved that the existing sewer collectors can handle the increased flow.