The quality and usability of water flowing out of the Korzeń stream catchment were assessed in order to determine whether it can be stored in a small retention reservoir. The Korzeń stream catchment (9.65 km²) is situated in the Tarnów county, in the hypsometric range of 231 to 397 m a.s.l. The investigations were conducted from January 2005 to December 2006. Water was sampled once a month. Temperature, pH, concentration of dissolved oxygen, degree of oxygen saturation, and electrolytic conductivity were measured on site, while total suspended solids, phosphates (PO₄^3–), ammonia(NH₄⁺) nitrites (NO₂^–), nitrates (NO₃^–), dissolved solids, sulphates (SO₄^2-), chlorides (Cl^-), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), total iron (Fe^2+/3+) and manganese (Mn²⁺), as well as BOD₅ (only in 2006) were determined in a laboratory. In terms of total suspended solids, iron and manganese concentrations, the water flowing out of the catchment may be classified into the 3rd class of water purity, i.e. into the waters with satisfactory quality. In terms of manganese concentrations, the water from the Korzeń stream would be fit for consumption only after a highly efficient physical and chemical treatment. Nitrites are the main component that adversely affects the living conditions of fish, whereas total suspended solids and water oxygen saturation sporadically do not meet the quality criteria for bathing water.

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