"In California, What Price Water?"

Not very much, it looks like.

"The San Diego County Water Authority has agreed to buy at least 48,000 acre-feet of water from the plant each year for about $2,000 an acre-foot. An acre-foot equals about 326,000 gallons, roughly enough for two families of four for a year. [...] The price of water the authority now gets from the Metropolitan Water District of Southern California is about $1,000 an acre-foot."

We had looked at this a couple years ago. This negotiated water supply is higher than the best case costs that were being tossed around there. Still, having an unlimited supply from the ocean at only 2x the current cost is not exactly the end of the world.