PWN considers ion exchange and ultrafiltration (IX-UF) for replacing the existing CSF pretreatment at the Andijk water treatment plant. Advanced oxidation (UV/H2O2) in combination with granular activated carbon filtration (GAC) as a non selective barrier against organic micro pollutants is operational since 2004. Effects of an improved pretreatment on the UV/ H2O2 in terms of direct photolysis, OH-radical oxidation and energy consumption are presented in this paper. NDMA and 1,4-dioxane are selected to show the impact of pretreatment on UV photolysis and hydroxyl radical oxidation, respectively. Key water quality parameters are DOC and nitrate for scavenging and competition for UV light. Compared to CSF, the electrical energy per order (EEO) for IX-UF treated water was reduced with about 50%.