The scope of this study was to investigate the fate and behavior of selected pharmaceuticals and main metabolites under defined conditions in model systems simulating slow sand filtration. For this purpose, analytical procedures were developed for the simultaneous identification and quantification of carbamazepine (CBZ), diclofenac (DCF), ibuprofen (IBU) and sulfamethoxazole (SFM). The following main metabolites were synthesized for method development: N-1-glucuronide-sulfamethoxazole (Glucu-SFM), N-4-acetyl-sulfamethoxazole (Ac-SFM) and 2- hydroxyibuprofen (OH-IBU). The procedures comprised solid phase extraction (SPE) for enrichment using polymeric material (Oasis HLB) and determination of the analytes with both GC/MS and LC/ESI-MS. For GC/MS, an additional derivatization step was necessary. Best results were obtained with the application of diazomethane as derivatizing agent. As a consequence, the determination of DCF, IBU and OH-IBU was preferably carried out by GC/MS, whereas SFM, Ac- SFM and Glucu-SFM were determined by LC/ESI-MS. CBZ could be sufficiently analyzed by both techniques, however, GC/MS is preferred because of much lower interferences by sample matrix. LC/ESI-MS allowed the measurement of the active drugs and their metabolites with quantification limits down to 10 ng/L in the MS/MS mode while GC/MS permitted the quantification in the same range or lower for some analytes, except SFM and its metabolites. The developed method was applied to real surface water samples from the river Ruhr, Germany.