A few hundred farms in the Imperial Valley of California adjacent to the Mexican border draw more water from the Colorado than all of Arizona and Nevada combined. Their inherited water rights take precedence over Arizona and Nevada’s water rights. In theory, that gives those farmers the right to entirely dry up those states and cities including Phoenix, Las Vegas and Tucson.
Clearly, there would be a tremendous political price to be paid if the farmers pushed that hard to fully exercise their rights.
Discussions are underway.