The western United States is characterized by highly variable and seasonal rainfall patterns. To deal with the constant threat of drought, the West relies on intensively managed water systems. Today, those systems face two challenges that were not anticipated when they were developed decades ago: increased demands that water be left in streams to sustain aquatic systems; and global climate change, which will decrease snowfall, leaving less water for farms and cities. The inevitable result is heightened conflicts over water allocation. As we pointed out in our 2008 book, Water War in the Klamath Basin, the U.S. has not yet shown the ability to cope effectively with water conflicts. In the drought summer of 2001, the Bureau of Reclamation shut down the headgates of the Klamath Project to conserve endangered species. Protests and violence followed. Some wet years have forestalled another shut-off, but the underlying causes of the conflict remain unaddressed. This March, the Bureau of Reclamation announced that it would delay irrigation deliveries to protect federally listed fish. Similar conflicts are heating up in the Sacramento River system. Crashing fish populations have forced reductions in water deliveries, and closed the ocean salmon fishing season for the second year in a row. It would be a mistake to simply ignore the environmental costs of established water diversions, as those calling for Endangered Species Act exemptions would have us do. Instead, we need to highlight the trade-offs among competing uses, and allocate our limited water resources in ways that recognize modern values. That means moving some water away from low-economic value farming to instream and municipal uses. That will not happen without pain, but it will be less painful if we do it now than if we wait for the next crisis. Holly Doremus is professor of law at the University of California-Davis. She has written extensively about biodiversity protection and the intersection of environmental law and natural science. A. Dan Tarlock is Distinguished Professor of Law at the Chicago-Kent College of Law. He was principal writer of the Report of the Western Water Policy Review Advisory Committee, Water in the West: Challenge for the Next Century.