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.
Your comment is a great example of the sort of zero sum ignorance that gets us where we are.
Yeah, you can always use state violence to take from one group and give to another but that's less than zero sum because it costs you use of state violence which isn't cheap and must be expensively maintained.
You might make things fairer doing that but you won't make them better overall. At some point for things to actually get better overall, for the pie to get bigger, you must actually build something for someone. If not a nuclear powered desalination plant then it will be something else.