Active pharmaceutic ingredients are necessary to fight illnesses, but we would not want to see them in our drinking water. However, many drugs are not or not effectively decomposed in the biological stages of the sewage plants. What is more, as these pharmaceuticals and their metabolites are highly water-soluble, they are not strongly bound to the sediments. Consequently, they travel from contaminated surface waters all into the groundwater. Over 100 different active pharmaceutical ingredients have so far been identified in the aquatic cycle, some with concentrations above the ecotoxicological no-observed-effect concentration (NOEC). The decomposition of pharmaceuticals using physicochemical methods, such as ozonolysis and adsorption to activated carbon, is either rather costly or the process itself produces toxic decomposition products.