Since the adoption of the European Water Framework Directive of 1991, the discharges of urban rainwater have to be reduced as much as possible. This theme is very sensitive in Berlin due to its drinking water supply system. The Integrated Sewage Management (ISM) project aims to improve the sewage system management, in order to reduce discharges and cut costs. The project is based on the modelling of the different parts of the system. This should lead to a global view of the way, how the system works and the implementation of a decision help tool for the operators of the Berlin Water Societies. A general description of ISM project and Berlin is followed by a presentation of Infoworks CS™. The building and calibration of Berlin V and XII models are explained and a last part presents tests of different ways to reduce rainwater discharges.