Aside from that, every year during the rainy season millions of gallons of water run down the Santa Ana River (and other rivers in this area) from the San Bernardino mountains and dump into the sea. Building a few extra dams would be a tremendous idea for making the southern part of the state more self-reliant. The Prado Dam is a joke, but there are plenty of other places where fresh water could be captured and stored.
And your idea about going nuke for electricity and de-sal water is just what we need, but somehow I don’t think the lefties in this state (or in the current federal administration) would ever allow it.
I do believe some things could be done along the lines of what you mentioned. I know it sounds unrealistic, but there are ways we could catch rain runoff on properties all over the southland, and save it in cisterns.
Water needs could be met for a month or two by using this water, and in good years, perhaps three months of water could be saved and used.
This water could be used for watering lawns, washing cars, and other things that might not require completely fresh water.
At my folks house in the foothills, they got over 45 inches of rain during the winter. You start thinking about the volume of water that represents over square miles of landscape.
I always thought that a folding system of plastic film could set up a natural runoff of water into a cistern and save literally thousands of gallons of water on just one property.
My folks have about half an acre. That should have worked out to about 2 acre feet of water on their property that year. If some way were devised to purify that rain water on their property, they could use it for all their needs. We might be talking about six months or more supply of water there.