You do understand that if you dig a depression for a pond in the desert, and fill it with salt water from the ocean, that the water will evaporate from the heat and dry air, and you will be left with a depression that used to be a pond that will be full of salt with little or no water, right?

The concept of removing the salt from ocean water is to provide fresh water for the cities along the ocean. If they did just that, and capped off the locations where they are currently pulling the water from the Colorado river basin to supply fresh water to those cities, it would probably solve both problems in a few of years.

Not building cities in the desert in the first place would have been the best correct response, but we are way past that point now.