Lake Tahoe's waters are so clear you can follow a diver 70 feet below your boat. A Lake Erie summer often means that nearshore waters have a green surface scum obscuring everything below. California, suffering from drought, is seriously considering reclamation and direct potable reuse of sewage -- aka toilet to tap. Can we (or should we) do this? Why is Tahoe clear, Erie green? This class introduces students to the fundamental tools and science used to understand and manage both natural and human-engineered water systems. Each student will use these tools to explore a water topic of their choosing.