The U.S. Supreme Court will soon decide a critical water rights case in the arid Southwest. The Navajo Nation extends into three states, and 30% of people who live on the reservation don't have access to running water. The tribe says the federal government broke its treaty promise to provide a sufficient water supply for the tribe and that it should come up with a plan to do so. But supplying more water likely means taking it from the lower Colorado River where water rights have already been allocated to Arizona, Nevada, California and others. Those states argue the Supreme Court already settled water rights on the river and the tribe's case should be thrown out.