Groundwater is a source for drinking water in many countries, and its use is seriously threatened by the leaching of agrochemicals through the soil. With this aim, the oxidation of triclopyr and fluroxypyr in water was investigated at lab-scale using heterogeneous photocatalysis and photo-assisted ozonation combined with hydrogen peroxide H2O2 (peroxone process). For both herbicides, the order of effectiveness of the photo-assisted treatments in pure water were as follows: O-3/H2O2>ZnO/Na2S2O8>TiO2/Na2S2O8. Comparing the three types of water, the rate constants through peroxone/UV process were in the order: Pure > Drinking > Leaching water, according to the complexity of the matrix. After two hours of treatment, fluroxypyr was completely removed from pure water, while 90 % and 55 % of its initial mass were removed from drinking and leaching water, respectively. On the other hand, the degradation of triclopyr was significantly slower. In this case, after two hours of illumination the complete degradation was not reached in any case. Owing to the generation of hydroxyl radicals (HO center dot) the water treatment with O-3/H2O2/UV can be considered as an eco-friendly technology, although the substances present in the matrix, mainly in leaching water, can scavenge HO center dot decreasing the photooxidation rate of both herbicides. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.