Pollution of soil and water environment by liquid waste originating from septic tanks is a huge problem in Poland. This applies especially to rural areas. Negative changes are observed both in the vicinity of the leaking tanks, from which concentrated and rotten sewage infiltrates into the ground, and in surface water as well as arable land, to which impurities from the emptied tanks are discharged. The paper presents the scale of the practice of uncontrolled domestic sewage discharge into the environment on the example of selected municipality. Presented data were compared with the results of the qualitative assessment of groundwater, which is collected in the same municipality for waterworks. In a significant number of wells, water was not safe in sanitary terms, as the presence of microbiological contamination was recorded. Among determined microorganisms, the indicator organisms of domestic waste pollution prevailed. Water quality problems have been reported at intake points located near the properties equipped with septic tanks or in places, to which sewage from emptying septic tanks were transferred in an uncontrolled manner. In this way it has been shown that there is a relationship between improperly maintained wastewater management and groundwater quality collected for the purpose of water supply.