California already has 12 desalination plants in use. Unfortunately none near Malibu or Pacific Pallisades.
Some are still in planning or construction. Some will probably never be completed. I think just 7 are operating and most are too small to really make a difference. The San Diego plant produces more than all the others combined, making 50M GPD. If CA had a dozen plants of this size, and the reservoirs to store the water, we would be doing fine. But CA will NEVER solve its water problem because we vote for idiots like Newsom.