The integrated information/decision support system presented in this paper is aimed at offering the users (e.g., government or municipal agencies, promoters, etc.) a flexible and user-friendly environment based on formal multiple criteria methodologies to assist them in keeping and structuring information, obtaining historical and statistical analysis, and providing decision aid by enabling a detailed comparative analysis of the alternatives in urban plans evaluation, both for experts and other people with no technical knowledge. The visualization of available alternatives on a map, assisting the user to locate the spatial elements in their actual environment, and the possibility of automatic representation of alternatives in the criterion space, provides a value-added for the decision analysis and support processes in urban infrastructure problems where usually several options must be compared. We present a SDSS prototype developed to plan and analyze a large-scale urban infrastructure investment decision in Coimbra, Portugal. The underlying decision is to select “the best” water supply system investment option to satisfy the new demand created by a proposed urban development/expansion project.