Das Projekt "Freisetzung von polyzyklischen aromatischen Kohlenwasserstoffen aus tauchgeteerten Rohren" wird vom Umweltbundesamt gefördert und von Stadtwerke Karlsruhe GmbH durchgeführt. Coal tar was commonly used for corrosion protection of cast iron and steel water pipes from the 19th century up to the present. It is reported, that these coatings can lead to elevated concentrations of Polynuclear Aromatic Hydrocarbons (PAH) in the distributed drinking water. A monitoring programme showed significant differences between parts of the distribution system which indicated that the chlorination of drinking water promotes the occurrence of PAH in the drinking water at the customers tap. Further field investigations showed, that there is a correlation between the chlorine or chlorine dioxide dosage and the PAH concentrations in the drinking water. Mechanisms for the occurrence of PAHs in these cases are the reduction of the microbiological activity (biofilm) and the mobilisation of corrosion products from the internal surface of the pipes during anaerobic conditions. These findings were be verified in a pipe rig under consideration of the effect of different hydraulic conditions. Also the formation of chlorinated PAH during the disinfection process was investigated.