Concentrations of people in urban areas intensify water problems such as flooding and pollution, but these deleterious effects on water resources can be minimized or corrected by comprehensive planning and management. Such planning of the water resources of an urban area must be based on adequate hydrologic data. Through the use of a matrix, urban water problems can be evaluated and availability of data assessed. The Washington-Baltimore metropolitan area is used as a case study. The completed matrix provides both a means for developing a meaningful dialogue between the hydrologist and the urban planner and a method for developing a work plan to insure consideration of water-resources data in urban planning.