Concentration of ions was examined in ground waters from post bog meadows. Samples of water were received in early spring and in September – from fertilized meadows and not fertilized meadows. In waters from the not fertilized meadow a higher concentration of ammonium ions and nitrogen ions was affirmed. Higher concentration of ammonium ions and nitrate ions appeared in early-spring period. High content of potassium and sulphates appeared in the water from fertilized meadows. High concentration of ion N-NH4, exceeding 1 mg/l qualifies the studied waters to IV class of cleanness. On non fertilized meadows there was weak sodding and lack of best grasses under cultivation. In these conditions quick mineralization of peat happened. Enlarged mineralization of peat caused strong eutrophication of ground waters with forms of nitrogen.