Modified version of the alkaline protocol described by Uhl et al.13 was performed with drinking water samples. Human hepatoma cell line (HepG2 cells) was obtained from prof. dr. Knasmueller, Institute of Cancer Research of The Univeristy of Vienna. Cells were grown in multilayer culture at 37 °C in humifiedatmosphereof 5% CO2 in Dulbecco’s ModifiedEagle’sMedium(DMEM) supplemented with 10% foetal calf serum (FCS) and antibiotic (0.1% gentamycin) in well plates for 7 days (cell density: 106–108 cells/mL). Medium was changed every 2 days. Seven days old cells were exposed to water samples, negative and positive controls (500 μM hydrogen peroxide) for 20 min and afterwards cell suspensions were prepared with 0.25% trypsin-EDTA solution, passed through injection needle for several times to achieve single cell suspension and finallyresuspendedinDMEM medium, supplemented with 10% FCS medium. The dye-exclusion test with Trypan blue was used to examine the viability of cells before the comet assay was performed.27