Quick Google stats: There are 13M households in California. Average household consumes 0.5-1.0 acre-feet of water per year. It costs $419 per acre-foot for desalination. California has a discretionary budget surplus of $49B. Thus: It would cost $2.7B-$5.4B per year to provide desalination-based water to all Californians. With the current budget surplus, we could provide 100% of California's living water needs for 10-…
I believe there are other, better ways to handle limited water supplies like finding inefficacies in the system and plugging those holes. Changing from mass monocultures to perma-cultures.
Unfortunately, they are much more boring than desalination plants.
There are great videos on this on YT, like [1]. Go and check them out.