Arizona and Nevada are faced with the first-ever cuts to their Colorado River water supply in 2020.
But the cuts aren't expected to be overly burdensome for either state because they've been conserving and storing water for years.
The water is delivered through Lake Mead, one of the largest manmade reservoirs in the country.
The U.S. Bureau of Reclamation says Lake Mead will fall below 1,090 feet on Jan. 1, triggering the cuts.
Arizona will leave 7% of its allocation in Lake Mead under a drought plan approved earlier this year by several states that rely on the river. Nevada will leave 3%.
Mexico also gives up 3% under a separate accord.
The states and Mexico can recover the water if Lake Mead rises to a certain level.