Since 1870 Riverbank filtration (RBF) on the river Rhine, Germany has been used successfully by the Düsseldorf waterworks as the first step for treating drinking water. The aim of this article is to present the experience in applying RBF with a focus on the purification efficiency of this natural treatment process. At the Düsseldorf waterworks, the influence of long-term as well as periodic changes of the river water quality on the RBF processes were investigated.

While for the first 80 years drinking water treatment was based only on RBF, additional technical treatment became necessary together with the decreasing Rhine water quality in the 1960's. The decontamination of the river was attended successfully by the waterworks along the Rhine. As a result of the increased river water quality the purification processes during RBF became again more efficient. However, periodic changes of river water quality and hydraulics influence the natural purification processes during RBF and have to be considered. Flood events are accompanied by shorter travel times and less effective natural purification. The changing river water temperature trigger a string of subsequent hydrogeochemical reactions within the aquifer. The performed investigations show that even during flood events and during extreme low water, the multi protective barrier concept including both natural and technical purification has proven to be a reliable method for drinking water production.