It’s a tantalizing question. As the Colorado River drought squeezes the Southwest, why not turn to the ocean for more water?
Now, the largest desalination plant in the Western Hemisphere could help make that a reality, purifying ocean water and helping boost Arizona’s drinking supplies.
The San Diego County Water Authority, which uses the desalination plant in Carlsbad, California, signed a Memorandum of Understanding to explore a water transfer program. It’s the first step in a process that could see the Phoenix and Tucson areas benefit from treated seawater.
SDCWA is able to decrease its own reliance on the Colorado River by pulling water from the Carlsbad plant, meaning that it doesn’t need to use its full allocation of Colorado River water every year. Under the proposed transfer system, SDCWA would leave some of that water in the river and let other water users — like the Central Arizona Project — pay to use it instead.
At a time when Central Arizona is facing the threat of deep cutbacks to its Colorado River supply, that is an attractive proposition.
The CAP, which brings Colorado River Water to the area through a 336-mile canal system, is one of the parties listed on the recent San Diego memo. CAP leaders said they are “open to further discussions” but have not yet committed to signing on.
Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University, said it could be a “very tidy solution to a really big problem.”
“I think it's a win-win,” Porter said. “San Diego County Water Authority has an overbuilt desal plant, and they would like help paying for that most expensive water and there are water users in southern Nevada and central Arizona that are urgently looking for new water supplies because they're facing uncertainty, except for certainly very deep cuts.”
Cost has proven to be a major limitation to expanding desalination operations around the Colorado River basin. The Carlsbad desalination plant cost $1 billion to build, and tens of millions to operate every year. For all that money, it produces relatively little water — about 10% of the annual supply for the San Diego area.
Those high costs mean that desalination produces expensive water.
While SDCWA has not named a sale price for transferred water, there are some clues. The water coming out of the Carlsbad facility today costs about $3,500 per acre-foot, according to SDCWA general manager Dan Denham. A series of projections from 2023 show the cost of water climbing past $7,000 per acre-foot in the 2040s.
For comparison, CAP currently sells its water for $365 per acre-foot.
An acre-foot is the amount of water needed to fill one acre of land to a height of one foot. One acre-foot generally provides enough water for one to two households for a year.
Porter said expensive desalinated water could make sense for Arizona under the right circumstances. With stalled Colorado River talks and the potential for deep cutbacks, the Phoenix area will likely have to look for new sources of water. Turning to transfers enabled by desalination could help fix that without engaging in the contentious process of buying it from farmers around the state, she said.
Brenda Burman, general manager of CAP, said there are still a number of hurdles to clear before the agency can sign on to SDCWA’s memo.
“It requires a lot of collaboration,” Burman told KJZZ. “It requires a lot of coordination to make something like this work, and so there are a lot of parties that all need to talk to each other.”
The MOU also seeks signatures from the U.S. Bureau of Reclamation, the Metropolitan Water District of Southern California, the Southern Nevada Water Authority and the Arizona Department of Water Resources.
The system SDCWA is proposing would create the first program to transfer water across state lines within the Colorado River basin. That fact, plus the kind of agencies involved, could reveal a number of legal issues.
Other states within the Colorado River basin could try to block it under certain interpretations of the century-old Colorado River compact. Differing interpretations of that 1922 document are already at the heart of major present-day disagreements about water sharing.
Even if that hurdle is cleared and CAP manages to buy water from San Diego, the agency will need to figure out which of its customers will get that water. CAP brings Colorado River water to Arizona, then sells it to more than 60 cities, tribes and businesses.
Buying transferred water from San Diego County, though, may be the easiest way for Arizona to tap into supplies from the ocean. The state appears very curious about desalination technology. Late last year, the Water Infrastructure Finance Authority voted to explore a number of different desalination projects.
In one proposal, Arizona is looking at building a new desalination facility in Mexico and exchanging the water it produces for some of Mexico’s Colorado River water. Building that plant would likely take years and massive sums of money.
A transfer with San Diego can happen much sooner and without steep upfront costs.
“We know large infrastructure projects take a lot of time,” Burman said. “Is this project the size that would cause us to turn away from other projects? No. I think everything should be on the table. We are out there trying to work with all possibilities, but, if you're looking at desalinization, it is the most immediate.”
Burman said the involved water agencies would have to sign the MOU before creating a timeline, but water transfers “could be done in a year, if everyone wanted to.”
“As the situation demands it, as the hydrology demands it, it's on all of us to develop more tools to manage [The Colorado River] system,” said SDCWA’s Denham. “And I think that this can be one of them.”
