UV/H2O2 treatment can be part of the process converting surface water to drinking water, but would pose a potential problem when resulting in genotoxicity. This study investigates the genotoxicity of samples collected from the water treatment plant Andijk, applying UV/H2O2 treatment with an electrical energy dose of 0.54 kWh/m3 and a H2O2 dose of 6 mg/l. Genotoxicity was tested in vitro using the Ames and Comet assay. All samples showed negative results. Samples were also tested in in vivo genotoxicity tests in Eastern mudminnow fish (Umbra pygmaea) by a sister chromatid exchange (SCE) and a Comet assay. No significant increases in SCEs were observed, but gill cells isolated from fish exposed to water obtained immediately after UV/H2O2 treatment and to Lake IJsselmeer water showed significantly increased DNA damage in the Comet assay. All other samples tested negative in this Comet assay. This indicates that DNA damaging compounds may result from the UV/H2O2 treatment, but also that these can be efficiently eliminated upon granular activated carbon (GAC) treatment of the water. It is concluded that when combined with this subsequent GAC treatment, UV/H2O2 treatment for the production of drinking water from surface water is not of concern with respect to genotoxicity.