The hydrochemical analyses of water inflowing, stored and flowing away from Mściwojów water reservoir were conducted from April to November 2012. Measured were 27 physicochemical indices of surface water sampled at 8 dates from four measurement-control points. Analysis of results revealed that water inflowing into Kałużnik river was the best quality – corresponded to class III, but only due to nitrate nitrogen. In the water Wierzbiak from the river, only two from among 16 indices exceeded class II (nitrate nitrogen and phosphates). Water in the reservoir was classified to quality class III because of the temperature and BOD5, similar as water flowing away from the reservoir. Moreover, the paper assessed usable values of inflowing water, stored in the reservoir and flowing away from it. On the basis of the analysis, it was stated that water cannot be supplied to people since it does not meet the requirements stated in the Minister’s regulations concerning the conditions of the natural habitat of cyprinids and salmonids.