The aim of this work was to point out the influence of sewage waste water from the home and other objects on the quality of selected watercourses. In the theoretical part I describe the distribution of waters, main polluters of watercourses, including their ingredients. I also focus on legislation where the pollutant limit values are given and their possible discharges into surface and groundwater. In the practical part I chose two watercourses in Slovakia, Teplica and Oravica flow and compared the results from the waste water treatment plant located in this territory with an impact on the effect on the relevant flow. In the end, the results are evaluated.