The combination of adsorption on particulate materials and electrochemical oxidation in 3D electrochemical systems is potentially a very efficient process for the treatment of micropollutants in water. This paper presents results on the use of granular activated carbon as particulate material in the process and treatment of the dye 4-nitrosodimethylaniline and pesticides MCPA (2-methyl-4-chlorophenoxyacetic acid), MCPP (2-methyl-4-chlorophenoxypropionic acid), and the pesticide transformation product BAM (2,6-dichloro-benzamide) in drinking water. 4-nitrosodimethylaniline was used to investigate influential factors as loading of GAC in a batch electrochemical setup and strength of the electric field in a flow cell recirculation batch setup. Results showed that compared to previous studies in distilled water, only additive effects were found in batch setup, and higher electric field strength was needed in the flow cell setup to achieve slight synergy (~ 5%). Reasons were likely due to the indirect oxidation pathways mediated by the anodic chloride oxidation induced by the content of chloride in the drinking water. On MCPA, MCPP and BAM synergies from 28 to 38% were measured in the batch setup, but in the flow cell, results ranged from additive effects (~ 0%) up to 70%. Considering the low price and widespread availability of granular activated carbon, the gain in process removal rates achieved in the combined 3D electrochemical reactor is of interest compared to the individual processes.