WaterSim on the Web allows anyone to explore the impacts of various scenarios of regional growth, drought, climate changes, and water management policies on regional water supplies and demand. This version was designed primarily as a teaching tool to be used by students and teachers to explore the dynamics of water resources management. An interactive tutorial on regional water resources provides an introduction to the water supplies and issues of the region and basic functionality of the model. Several predefined scenarios are available. The scenario builder allows custom scenarios to be created and graphs of results of the scenarios viewed. A mini version of WaterSim in the Decision Theater is provided allowing various factors to be set with results viewed in real-time. The lesson outlined below was developed for use in AP or introductory college-level Geography or Environmental Science classes.