Due to the sensitive situation of watercourses in the urban area of Berlin the water authorities have set special conditions for discharge especially from combined sewer overflows. To meet the legal requirements a central task is to reduce the pollutant load discharged into receiving waters and for this purpose the intelligent utilisation of the available capacities of the entire waste water system. Measures of local real-time control have already been implemented in the Berlin drainage system. This paper is focusing on the potential of an additional superior global control concept. Comparative simulations for three interconnected subsystems are carried out to evaluate different operational alternatives.