Urban wastewater system, a hydraulic infrastructure consisting of elements such as pipes, tanks, junctions, pumps, and valves etc., is crucial to drain wastewater from urban areas. Effective wastewater system is of paramount importance in designing a urban waste water network or in expanding the existing one. It is essential to investigate and establish a reliable network ensuring adequate head. However, the optimal network design is quite complicated due to nonlinear relationship between flow and head loss and the presence of discrete variables, such as market pipe sizes. Subject of study are settlements Dobova, sela pri Dobovi, Cundrovec and Bukošek in the municipality of Brežice. The above mentioned villages are detailed onceptual design solutions discharges and wastewater treatment. They offer the following variants: VARIANT I: sewerage systems to individual small treatment plants (sewerage system Cundrovec, sewerage system Bukošek, sewerage system Sela pri Dobovi and Sewerage system Dobova), VARIANT II: sewerage system with more common small treatment plants (sewerage system Cundrovec-Bukošek and sewerage system Sela pri Dobovi - Dobova) and VARIANT III: sewer system with common sewage treatment plant (sewerage system Cundrovec-Bukošek-Sela pri Dobovi-Dobova). In the last part of the study construction cost are calculated, operation and maintainance of each system, and based on cost analysis of selected rational and economically most suitable variant.