Cut off power and water to CA.
That is the key.
Since most of California’s population is now either descended from illegals, or are actually in the country illegally, the other Western states have no obligation to honor the Interstate Water Compact that splits the water up.
The agreement was not made with the idea of supplying water to foreigners.
That’s my solution, too. Under the Colorado River water laws it gets 7.5 maf water from the overall basin states comprising the Colorado river basin and another 4.5 maf from the lower basin states. [millions-of-acre-feet]