The study evaluates the impact of small domestic wastewater treatment plants (SDWWTP) working on the principle of the activation processon the water quality in small recipients. The water sampling was carried out above and below domestic wastewater treatment plant’s outflow, from September 2014 to August 2015, regularly every month. All samples were collected and determined as per the applicable standards. Results were evaluated on the basis of current surface water legislation and compared with environmental quality standards (EQS) contained in Government Order No 23/2011 Coll., on Indicators and Values of Permissible Pollution of Surface Water and Wastewater, Mandatory Elements of the Permits for Discharge of Wastewater into Surface Water and into Sewerage Systems, and on Sensitive Areas. Water analysis in recipients under SDWWTP has shown high concentrations of total phosphorus and ammoniacal nitrogen. At the same time, reduced concentrations of dissolved oxygen were analysed below domestic wastewater treatment plant’s outflow, where two SDWWTP has shown increased concentrations of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). Not working nitrification process is a consequence of high concentrations of ammoniacal nitrogen due to low concentrations of nitrite nitrogen and nitrate nitrogen.