Also in new process trains for potable water production including ozonation, activated carbon and membrane filtration, activated carbon contributes substantially to quality improvement and assurance. The treatment fulfills three tasks such as particle separation, adsorption and fixed bed biofiltration. Experiments with lake water reveal that fresh activated carbon exhibits an enormous capacity to adsorb specific micropollutants as well as fractions of the natural organic material (NOM) which may have detrimental effects on subsequent ultrafiltration. Unfortunately, the presence of certain high-molecular NOM fractions leads to a rapid decrease of the adsorption performance. On the other hand, microbiological growth and attachment takes place within a few weeks of filter operation adding to the production of a biologically stable drinking water.