The ground water quality was determined after the analyses of water samples from 18 wells. The wells were in the Groundwater Area with the Highest Protection (Triassic water, Opole region, Poland), rural build up. The water table level was low: 0.5 – 18.0 m below the ground surface level (except for one artesian well). The following parameters were determined: pH, EC, colour, ammonium, nitrite, nitrate, dissolved orthophosphate, total phosphorus, dissolved oxygen, BOD, COD-Mn, COD-Cr, humic substances, chloride, sulphate, total hardness, alkalinity, dry residue PAHs (16 compounds), pesticides (6 compounds), however, only selected data were presented in this paper. In all the analysed water samples chloro-organic pesticides were observed. The analysed water contained heptachlor in the highest concentrations of 15.97 mg/dm3. Good quality water must not include concentrations higher than 0.5 mg/dm3 of heptachlor. However, the concentration was circa 32 times higher than this value. The second pesticide determining poor water quality is dieldrin. This compound in the investigated groundwater was 1.94 mg/dm3 – 4 times higher than the limit for acceptable quality ground water. The concentration of pesticides also changed over the course of the research; the concentration in the analysed groundwater in the same well changed quite dramatically over a period of 1 year. Although PAHs and pesticides are potentially toxic for biological organisms they do exist in the environment as a product of the natural biological transformation of organic matter. The noted concentrations and compositions of PAH compounds were different to natural PAHs. It confirms the fact that agricultural activity influences groundwater quality.