The objective of this study was to investigate genotoxicity, especially DNA damage, in drinking water samples collected from tap by using fission yeast Schizosaccharomyces pombe as a model organism. Generally raw water potabolization is done by treatment with polymeric coagulant, alum, chlorine, etc. In the comet test, highly significant (P<0.001) effects of DNA damage were detected in treated water (tap water) when compared to negative control (raw water) as well as laboratory control (distilled water) samples for both 1 h and 2 h exposure. In the water treatment plant, raw water treatment is done by the process of prechlorination, alum and polymeric coagulant (CatflocT) dosing, postchlorination, filtration and final discharge for consumption. In conclusion it can be stated from the results that chlorinated disinfectant, alum and polymeric coagulant (CatflocT) mixture used in drinking water has a potent cumulative genotoxic effect in the eukaryotic cells and may pose potential genotoxic risk for human health following long-term consumption.