The paper discusses the integral indicators of the quality or level of contamination of natural waters, allowing for an assessment of their ecological status. It has been established that the criterion for the quality of treated wastewater discharged into a water body is a regulatory allowable discharge, but it is not always possible to calculate it, especially for small rivers characterized by low flow rates of the river runoff compared to the flow of wastewater. An integral indicator is proposed for assessing the level of pollution of wastewater discharged, a formula for calculating it, as well as criteria for assessing the quality of wastewater discharged according to the proposed integral indicator. The method of calculating the integral indicator is based on the assessment of the quality of wastewater discharged in terms of BOD5, dissolved oxygen, and nutrient elements. Using the wastewater discharged from the Novocherkassk wastewater treatment plant as an example, an integral indicator of the level of contamination was calculated, which made it possible to characterize the wastewater discharged as “dirty” and make a conclusion about the need for additional treatment.

Keywords: wastewater, water pollution level, integral indicator of water quality, sewage treatment facilities