Avoiding a long-expected crisis on the Colorado River, a water source for 40 million people, is coming down to a final few days of frenzied negotiations. A 19-year drought and decades of overuse have put a water shortfall on the horizon. If California and six other states, all with deeply entrenched interests, can’t agree on a plan to cut their water consumption by Jan. 31, the federal government says it will step in and decide the river’s future.