Predjama, Bukovje, Gorenje and Belsko in the municipality of Postojna do not have a wastewater disposal system. The basics of wastewater treatment plants and sewage systems are presented in this thesis. A conceptual design for a sewage system for the disposal and treatment of wastewater and precipitation water is also presented. The choice of technical solutions took account of the rugged nature of the terrain, which limited the use of a gravity sewage system, and the sensitivity of the karst area in which the settlements are located. Two solutions were proposed, both of which would replace the existing method of wastewater disposal in flow-through or non-flow-through septic tanks in an ecologically and legally acceptable way. Based on a financial analysis, the task identified the more favourable solution. A layout of the proposed route and longitudinal profiles have also been drawn up for the proposed new sewage system.