The issues of determining the quality of wastewater are relevant for various countries within the framework of environmental regulation. The methods used for calculating the quality standards of wastewater discharged into reservoirs have different degrees of justification and, thus, can cause systemic errors in the analysis of the quality of treated wastewater. Another reason for possible inconsistencies is errors in the unrepresentativeness of analytical studies and sampling procedures. Based on the fact that average values, including annual averages, are used to determine the acceptable quality of wastewater treatment, this article shows options for negative impacts on water bodies from various objects, taking into account the real contribution to the volume of such negative impacts.