There are plans to build a desalination plant in the Bay Area [1]. This and other plants in CA could help water supply in populated areas.

The water districts in CA have two problems: 1. They are not connected well so water cannot easily be transfered from one district to another. 2. The reservoirs cannot sustain an extended drought.

[1] https://portal.ebmud.com/our-water/water-supply/long-term-pl...