The Tuzla region of Istanbul, Turkey, where surface water is one of the important sources for drinking and irrigating water, is heavily polluted by industrial and agricultural wastes. The cytotoxic and genotoxic potentials of water samples collected from Tuzla were investigated by the umu-assay, using the Salmonella typhimurium TA1535/pSK1002 as tester strain in the presence and ab-sence of metabolic activation. Different techniques were tried to extract and concentrate genotoxins from water samples. Water samples spiked at four concentrations of two positive controls, 4-NQO and 2-AA, were used to evaluate the efficacy of four concentration techniques. amberlite XAD-2 resin, Oasis (R) HLB, octadecyl silica (C-18) and styrene divinylbenzene (SDB) columns. Genotoxicity of both the untreated and the 2000-fold concentrated water samples were determined. We conclude that for the determination of genotoxic potential in water samples, XAD-2 resin is the most sensitive and convenient of the four methods examined. The obtained results suggest that four samples collected from two parts of Tuzla region present genotoxic risk in the absence and presence of metabolic activation. Additional studies are required in the analytical field in order to identify and quantify the compounds responsible for the genotoxicity in these areas.