Santa Barbara is demothballing its 20 year old desal plant that has never been used. Cambria CA is just now commissioning its new desal plant. The Diablo Canyon Nuclear plant has used desal for all of its potable and process water since commissioning.
One interesting thing is that most desal plants here don't use direct seawater. They pump brackish water from near shore wells. The salt content may be less, but mainly, the water is already filtered, saving some expense and steps in the process.
The City of San Luis Obispo has been recycling some of its wastewater for more than 10 years, irrigating parks, the golf course, and landscaping with it. If you are adjacent to a purple water line, I believe you are required to use reclaimed water.
Another interesting factoid... Even thought all of the City's potable water is imported from other watersheds, or pumped from wells, it is required to continue dumping enough treated effluent into the creek to keep the stream live year around all to way to the Pacific.