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