Usually sewage water is return back to the natural water flows. In the course of our examination we investigated the effect of the cleaned sewage to the receiver canal. We planned the time and places of the samplings. We examined the water chemical components of the cleaned sewage before and after entering the Kakat - brook. We carried out water analytical tests in the laboratory of the Department of Environmental Engineering, Faculty of Engineering, University of Debrecen and nearby the canal. We compared the results with the limit values of regulations.