In order to facilitate urban water managers developing alternative ways of dealing with storm water, an interactive decision support system has been developed. It is called “IBOS Regenwater” (Dutch abbreviation for: Interactive Decision Support System for Storm Water) and can be used on the Internet: http://www.ibosregenwater.nl. The decision support system focuses on local projects. It results in a well argued policy line for storm water management that is adapted to the specific local conditions. The main characteristics of IBOS Regenwater are the easy access of GIS-based information and a clear decision support concept, resulting in only four steps to be taken by the user. IBOS Regenwater supports different ways of obtaining information related to the local possibilities. It provides access to databases for national legislation, regional policy guidelines, case studies, drainage methods and BMP’s. The methodology is based on 5 principle mechanisms for dealing with storm water: usage, retention on the surface, infiltration, discharge to surface water or, as the last option, discharge to a WWTP. The DSS supports the water managers in creating alternatives. The DSS subsequently assessed the environmental effects and the resources needed to realise and maintain the specific alternative.