In the surface waters of the rivers Rhine and Meuse, twelve drugs that are listed in the Dutch Opium act were detected at low concentrations. They are from the groups amphetamines, tranquilizers (barbiturates and benzodiazepines) opiates and cocaine. During drinking water production, most compounds are removed or concentrations are substantially lowered. In finished drinking water, three barbiturates were still detected in very low concentrations (up to 12 ng/L). The amounts are below health based provisional drinking water limits. Ongoing monitoring of the presence of these compounds in water and possible long-term effects on human health are a point of interest. It is recommended to investigate possible ecotoxicological effects. These findings are the results of a RIVM investigation performed under the authority of the VROM-Inspectorate of the Dutch Ministry of Infrastructure and the Environment. This investigation was carried out in cooperation with KWR Watercycle Research Institute and the Research Institute for Pesticides and Water of the University Jaume I (Spain). A total of 65 water samples were analysed for 37 different drugs of abuse and metabolites. In addition to surface waters and drinking water, sewage waters were also analysed. The compounds can be detected due to the increased sensitivity of analytical methods nowadays available. However, drugs have probably been present in the aquatic environment since they have been used by humans. Substantial fractions of the total load of drugs in the Rhine and Meuse rivers enter the Netherlands from abroad. There is also a contribution through effluents from sewage water treatment plants in the Netherlands. The concentrations found in Dutch sewage water are in the same range as concentrations found in other Western European countries. Based on the measured concentrations, cocaine consumption in some Dutch cities could be estimated and compared.