Few of us, even among professionals who think about specific aspects of water every day, have ever thought about the water environment of cities. What does this mean, and why is it important? Some aspects may be familiar, whereas others are out of sight, and others are conceptual constructs. Parts of the urban water environment are obvious. Water features are often the heart and soul of many cities. Chicago's Lake Michigan shoreline, the Chain of Lakes park system and the Mississippi riverfront in Minneapolis (Fig. 1.1), and Boston's Emerald Necklace define these cities and make them uniquely livable. These water features renew the soul.