Israel gets over 50% of their potable water from de-salinization plants, and about 85% of its drinking water. They have 5 major ones and 30+ smaller ones.

Without being an expert, if I had to guess environmental more than financial costs are the reason CA doesn’t have more of these. 

Worth mentioning given all the lack-of-water issues in CA, and not having reservoirs filled for the Palisades / LA fires.