The European DayWater project has developed a prototype of an Adaptive Decision Support System (ADSS) related to urban stormwater pollution source control. The DayWater ADSS greatly facilitates decision-making for stormwater source control, which is currently impeded by the large number of stakeholders involved and by the necessary multidisciplinary knowledge. This book presents the results of this project, providing new insights into both technical and management issues. The main objectives of its technical chapters are pollution source control modelling, risk and impact assessment, and evaluation and comparison of best management practices. It also covers management aspects, such as the analysis of the decision-making processes in stormwater source control, at a European scale, and stormwater management strategies in general. The combination of scientific-technical and socio-managerial knowledge, with the strong cooperation of numerous end-users, reflects the innovative character of this book which includes actual applications of the ADSS prototype in significant case studies. DayWater: an Adaptive Decision Support System for Urban Stormwater Management contains 26 chapters collectively prepared by DayWater scientific partners and end-users associated with this European Research and Development project. It includes: A general presentation of the DayWater Adaptive Decision Support System (ADSS) structure and operation modes, A detailed description of the major components of this ADSS prototype, The assessment of its components in significant case studies in France, Germany and Sweden, The proceedings of the International Conference on Decision Support Systems for Integrated Urban Water Management, held in Paris on 3-4 November 2005. The book presents the ADSS prototype including a combination of freely accessible on-line databases, guidance documents, road maps and modelling or multi-criteria analysis tools. As demonstrated in several significant case studies the challenge for stormwater managers is to make the benefits of urban stormwater management visible to society, resulting in active co-operation of a diversity of stakeholders. Only then, will sustainable management succeed. DayWater: an Adaptive Decision Support System for Urban Stormwater Management advances this cause of sustainable urban management through Urban stormwater management, and makes achievable (by means of risk and vulnerability tools which are included) the goal of integrated urban water management (IUWM).