Desalination has been the technological breakthrough of next Tuesday for most of my life. I’ll be happy to see an actual deployment. Until then we wait.
Cut the water supply and LA will do fine, but the farms will die. (Millions of voters vs. a handful of relatively minor donors. It's an easy decision.)
It produces some pretty nasty byproducts, so a tough sell in California, but affordability is a total non-issue.