The paper describes the effect of the amount of wastewater flowing in a small sewer system to changes in the concentration of pollution indicators: Total suspension, BOD5 and COD. In order to determine the dependence described were used statistical analysis of Pearson`s correlation. In the 6 year study period from 2009 to 2014 were collected and analyzed 31 samples of raw wastewater. Determine the correlation based on the rejection of outliers based on the analysis of residues and the calculated distance Cook`s included 29 results wastewater analysis. The analysis showed that along with the increasing amount of waste water in the sewer decrease the concentration of pollutants in raw wastewater. In the case of BOD5, it was found that the increase in influent about 1 m3 to decrease the value of this parameter by 0.86 g O₂ · m^–3. In the case of COD with the quantity of sewage in the sewer 1 m3 of this ratio decreases by 1.73 g O₂ · m^–3. In relation to the concentration of total suspension it found that the increase in the amount of sewage flowing into the sewage system reduces the concentration of total suspension of 0.73 g · m^–3.