The main body of research on pesticide removal with membranes has looked at pesticides used for pest control, but during transport from surface to groundwater aquifers, pesticides are transformed. Therefore the real polluting compounds are often transformation products, and this vastly increases the total number of pollutants in need of treatment, which also creates a need for a simple way of predicting expected rejections to avoid the daunting task of investigating all these experimentally. In this study, the applicability of NF/LPRO/RO membranes for treatment of groundwater polluted with some of these key transformation products is assessed experimentally and compared to that of regular pesticides. Also, it was investigated whether the rejection could be modelled with a simple steric model. It was found that NF membranes capable of rejecting the regular pesticides did not give satisfactory rejections of the transformation products, mainly because of the reduced size of these. Further, the rejection could be described with a pore flow model, but different definitions of the molecular width were needed to describe rejection for NF and LPRO/RO membranes. With the model it was predicted that rejections over 90% can be obtained with an LPRO membrane for most pesticides and transformation products found in Danish groundwater. (C) 2014 Elsevier B.V. All rights reserved.