The genotoxicity of drinking water treated with 6 disinfection methods and the effects of disinfection conditions were investigated using the umu-test.The pretreatment procedure of samples for the umu-test was optimized for drinking water analysis.The results of the umu-test were in good correlation with those of the Ames-test The genotoxicity and production of haloacetic acids (HAAs) were the highest for chlorinated samples.UV + chloramination is the safest disinfection method from the aspects of genotoxicity,HAA production and inactivation effects.For chloramination,the effects of the mass ratio of Cl2 to N of chloramine on genotoxicity were also studied.The changes of genotoxicity were different from those of HAA production,which implied that HAA production cannot represent the genotoxic potential of water.The genotoxicity per chlorine decay of chlorination and chloramination had similar trends,indicating that the reaction of organic matters and chlorine made a great contribution to the genotoxicity.The results of this study are of engineering significance for optimizing the operation of waterworks.