Studies were carried out on the content of NH4-N, NO2-N, NO3-N and numbers of bacteria indicatory of water pollution (TVC 20 degreesC, TVC 30 degreesC) and its sanitary state (TC, FC, FS) in deep wells and shallow piezometric boreholes, as well as on bacteriological contamination of water in rivers Sawica and Omulew, in the area of water-bearing formations of Omulewski Aquifer (with no isolation from the surface), in 1995-1997 (after liquidation of the majority of large cattle and pig breeding farms in this area). The following were distinguished: 1. wells in afforested area in Sedansk and Narty, 2. wells located in farm lands of individual farmers in Jedwabno and Kot, 3. wells located in breeding farms of foxes, cattle and pigs in the villages Janowo, Dzierzki, Wesolowo, Wielbark, Przezdziek, Baranowo, Wyzegi, and 4. piezometric boreholes in the cattle farm at Wesolowo. Water of Sawica River (together with water from trout ponds fed by this river) and of Omulew River were analyzed at Janowo, Kot, Wesolowo and Wielbark, close to respective wells and boreholes. The degree of chemical and bacteriological contamination of well waters was diversified, depending on current and earlier use of land in the area of Omulewski Aquifer. NH4-N content decreased in well and borehole waters located in the area of former cattle and pig farms at Dzierzki, Wesolowo, Przezdziek, Baranowo and Wyzegi compared to the levels found in 1989-1993. Notwithstanding this, its level in some wells exceeded 0.5 mg/l NH4-N, i.e. the maximum level permissible in drinking water and water used for household purposes. As regards the sanitary state, only wells in Sedansk conformed to the standards for drinking and household water. Contrarily to what was expected, there was no decrease of indicatory bacteria numbers in water of wells and boreholes located in the area of former large cattle and pig farms. Water in deep wells at Kot, Wesolowo and Wielbark usually contained higher numbers of indicatory bacteria in the periods when their levels increased also in Sawica and Omulew rivers.