Dammed drinking water reservoirs with their catchment areas and the downstream rivers are dynamic systems that change permanently under the influence of many factors. Their multifunctional use for drinking water supply, flood control, energy production, nature conservation and recreation as well as ecological constraints for the rivers downstream requires an integrative management considering and balancing between different requirements. Thus, an optimal reservoir management has to take into account scenarios of external influences and must be based on predictions of prospective raw water qualities. Furthermore, the impacts of short- and long-term changes of the raw water quality on drinking water treatment have to be considered. The problem is very complex and cannot be solved intuitively but requires the application of hydrological, ecological and process models. This approach was followed in the work presented here, as a tool to predict and evaluate the impacts of different reservoir management strategies in an integrative way is currently not available. The developed decision support procedure (DSP) allows for the estimation of the effects of different hydrological and water quantity management scenarios on raw water quality, water processing costs and ecology in the downstream river. Extreme hydrological events or changing boundary conditions (e.g. climate change) are taken into account.