You don't have an energy problem, you have a political problem. Fresh water is wasted on thirsty plants destined for agriculture (like alfalfa), by rich farmers who inherited water rights put into law ages ago. It's very simple to solve water usage in California, it just requires a governor that has a tiny amount of grit and cuts into their water rights.

It's crazy how to some, building a whole nuclear reactor and dozens of desalination plants seems like a simpler solution than making a couple of very wealthy farmers a bit angry for a while. Capital really is all-powerful in the States, it even holds power in the very minds of its citizens.