The authors investigated drinking water from three plants in Northern Moravia with regard to genotoxic effects which are frequently potentiated by the method of chlorine treatment. Water samples, plain and treated , were tested by Ames test and the SOS chromotest. In both short-term tests the genotoxicity of drinking water was confirmed, whereby after disinfection by chlorine treatment the geno- toxic potential of water samples increased. On comparison of drinking water treated with gaseous chlorine and chlorine dioxide the latter had more favourable parameters from the genotoxic aspect.

        Key words: genotoxicity - drinking water - chlorine - chlorine dioxide - Ames test - SOS chrmotest