Arizona, Nevada and Mexico will start taking less water from the Colorado River in January as a hard-fought set of agreements kicks in to reduce the risk of reservoirs falling to critically low levels. The two U.S. states agreed to leave a portion of their water allotments in Lake Mead under a deal with California called the Lower Basin Drought Contingency Plan, or DCP, which the states’ representatives signed at Hoover Dam in May. California agreed to contribute water at a lower trigger point if reservoir levels continue to fall. And Mexico agreed under a separate accord to take steps to help prop up Lake Mead, the nation’s largest reservoir near Las Vegas, which now sits 40% full after a nearly 20-year run of mostly dry years.