Is Desal Really Only an Option at the Margins?

Rob Davis at Voice of San Diego has a nice overview of the proposal being considered to build a desalination plant on the coast of Baja, near Tijuana, to provide water for U.S. and Mexican users:

Together with the Mexican government, the agencies supplying San Diego, Los Angeles, Las Vegas, Phoenix and Tucson are studying whether to build a seawater desalination plant in Mexico capable of producing 50 million gallons of water daily, enough to supply 112,000 homes, as a way of reinforcing water reliability in both countries. Water would either be pumped to the United States or swapped for the rights to some of Mexico’s share of the Colorado River.

One hears a lot of talk about desal in discussions of augmentation of Colorado River supply. David Zetland calls its cost the “backstop price” for water in the southwest, meaning that once other options get more expensive, people will just build a bunch of desal plants on the coast and then swap around water inland.

But what struck me about this project, as Rob describes it, is how small it really is. 50 million gallons per day is about 56,000 acre feet per year. The average Lake Mead shortfall during the ’00s was 1.2 million acre feet per year. That’s the supply-demand imbalance we’re talking about. That would mean 20-plus desal plants just to close the current gap.

As Rob’s article notes, there are two currently under discussion of similar size – the Rosarita project and Poseidon up the coast in the U.S. Both have very long time lines.

Does this suggest desal is unlikely to be a very big piece of the long term supply picture?

(Rob’s article also has some interesting discussion of U.S. and Mexican regulatory issues, and the idea that putting the plant in Mexico is just easier. Good read for that issue as well, separate from the issues I’m raising here.)


  1. That plant is being discussed as a way of taking more CR water for Vegas et al., but they should be able to swap 1+ AF of CR water for each AF of VERY CLEAN desal water.

    That said, it’s a technology solution that “makes sense” in the absence of proper resource management. It’s also a backstop in the sense that there’s no large scale technology that’s more expensive — not b/c it’s unlimited in supply…

    Oh, and Vegas could cut it’s use by 30+ percent by making heavy use more expensive.

  2. For the City of San Diego desal will certainly be on the margins. The city itself only buys raw untreated water for its three water treatment plants. While the County Water Authority is in the thick of things with the Poseidon desal plant (which as you’ve noted will also be only a 50mgd operation), that water will go into CWA’s treated water distribution system serving other member agencies in the county.

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