Why not just let who owns the rights sell the water to the highest bidder at a free-market price?
The side benefit is that lettuce farming in the desert might diminish, and we ended up buying lettuce grown in Mexico—so we won’t “need” to have the illegals come here to pick it.
...but who “owns” the river?? That’s the whole point, and precisely why we have a federally brokered water compact.