When a storm occurs, the water that gathers can cause irreparable damage to the surrounding areas. In an urban environment this can cause havoc not only for residents but damage buildings and endanger safety. The white paper presented as part of the DAYWATER project, examines the risks relating to storm water effects on cities. Amongst other achievements, the paper emphasises the importance of the public perception of what constitutes a risk. It states that an individual's perception of the same risk varies a lot. After looking at definitions the paper turns to explore risk management itself. It presents a framework for risk analysis. A draft outline of the tool for screening potential storm water pollutants is presented. These tools will have potential applications both within hazard and vulnerability identification and assessment. The paper also addresses the subject of uncertainty in risk management. It constructs a matrix for analysing uncertainty when making decisions relating to urban storm water management. The paper demonstrates that decisions can be divided into four different regimes. These are based on differences of opinion of what the goal may be and on knowledge available regarding the technology needed to achieve the goal. Finally, results are presented of questionnaires that have been conducted as part of the project. A matrix was drawn up, which divides the urban storm water system into seven different risk objects and seven different types of risk.