Robbie, that water in lake mead is colorado river water, 7 states and mexico have rights to that water from the beginning.
The Colorado River Compact is a 1922 agreement among seven U.S. states in the basin of the Colorado River in the American Southwest governing the allocation of the water rights to the river's water among the parties of the interstate compact. The agreement was signed at a meeting at Bishop's Lodge, near Santa Fe, New Mexico, by representatives of the seven states the Colorado river and its tributaries pass through on the way to Mexico.
Colorado River Compact - Wikipedia, the free encyclopedia