They wouldn't if you switched just Urban water use from natural sources to desalination. To do that you need to replace the ~5 million acre feet of water, ~6,167,400,000 m3, that goes into the Urban bucket which is all of the water used to keep people alive, clean, and all industrial uses of water. [0] That comes to ~ 12BkWh of energy needed to scale up batched reverse osmosis to take over just the life and job required water needs which is about 25% of the total solar power generated in all of 2025 via grid-scale solar farms. CA does export some during the day due to excess solar but is still a net importer of power.

[0] p2 of https://cwc.ca.gov/-/media/CWC-Website/Files/Documents/2019/...

> California pays other states to take its excess solar energy

Intermittently. Essential services like water (with expensive fixed costs) aren’t a good fit for absorbing variable supply.

> Power for a project like this isn't the issue

California has the country’s most expensive power [1] in part due to policymakers constantly assuming it’s free.

[1] https://www.electricchoice.com/electricity-prices-by-state/