Sustainable management of any physical resource requires a good understanding of the distribution and quantities of that resource. Thus, information is highly valuable but it can be complex and hard to manage. Integrated management approaches in particular require massive amounts of spatially and temporally varying data from many different sectors: the quality and quantity of water resources; the geography of the area; the local geology and soil; the human communities; and the land use patterns is all important and interrelated information. One of the biggest challenges in IWRM today is to represent the full scope of this information, of the variables, interactions, and complexity that every water project and policy is confronted with. Analytical tools are needed to interpret the data in a way that makes it usable for decision makers. Models and Decision Support Systems (DSS) do exactly that.