View of a canal in Imperial Valley on Nov. 15, 2022.
View of a canal in Imperial Valley on Nov. 15, 2022. / Photo by Ariana Drehsler

If you live in San Diego, chances are a large portion of the water pouring from the tap, refilling the toilet tank and sprinkling the lawn comes from the Colorado River. 

Fed by melting snowcaps in Colorado’s Rocky Mountains, today that river provides about 72 percent of San Diego’s water after it travels through an aqueduct from Los Angeles and another pair of pipes managed by the San Diego County Water Authority.

In the 1940s, the San Diego Water Authority bought almost all the water the growing city needed from the Los Angeles Metropolitan Water District, which maintains Southern California’s direct connection to the river. But a severe drought in the 1990s forced drastic water cuts statewide and convinced San Diego to diversify its sources.

Most of San Diego’s water still comes from that same river and through those same pipes. What’s changed is who San Diego pays for the water. Increasingly, the region buys its water from the Imperial Valley, instead of Los Angeles which ties San Diego’s fate ever faster to the dwindling supplies of the Colorado River.

Imperial Valley

Alex Jack of Jack Brothers, Inc., looks at his lettuce growing in Imperial Valley on Nov. 15, 2022. San Diego pays for water conservation projects on Imperial Valley farms in exchange for some of the farmers’ Colorado River water. / Photo by Ariana Drehsler

Nearly three quarters of San Diego’s water comes from the Colorado River, and a whopping 59 percent of that is supplied through a deal made in 2003 with the Imperial Irrigation District in the eastern neighboring county home to a $2 billion agriculture industry. 

The deal works like this: San Diegans pay for water conservation projects on Imperial Valley farms in exchange for some of the farmers’ Colorado River water. San Diego also helped pay to pave-over earthen water canals, which prevents excess water from seeping into the soil when its transported, in exchange for the water preserved by that concrete lining. About 43 percent of San Diego’s supply comes from the farm conservation program, and the other 16 percent from the canal-lining project, according to the Water Authority.  

In the water policy world, that deal is known as the QSA or “quantification settlement agreement,” and it’s one of the largest water trades between agriculture and urban area in U.S. history. 

Farmers don’t physically send the water westward through canals or pipes to make that exchange. San Diegans are instead consuming water on paper, tracked using legal instruments to determine who is paying for and consuming water molecules circulating throughout the West.

“It becomes part of the Colorado River accounting,” said Dan Denham, deputy general manager of the Water Authority. “It’s not like a real time hand on the faucet turning it on and off.”

Employees at the Imperial Irrigation District in Imperial Valley on Nov. 16, 2022. / Photo by Ariana Drehsler

San Diego’s water still travels through Los Angeles’ connection to the Colorado River through the Metropolitan-owned Colorado River Aqueduct, a 240-mile straw from the Colorado River to Southern California. The water then travels south through two additional aqueducts built between LA and San Diego that terminate at a reservoir in Otay. 

Water supplied by LA typically includes a mix of Colorado River water and some meltwater from the Sierra Nevadas in northern California, provided by another delivery system known as the State Water Project. The latest drought took a large toll on that northern California supply as well to the point where LA wasn’t sending any of that water to San Diego, according to Water Authority officials. Only five percent of that supply will be available in 2023, according to the state Department of Water Resources, pushing Angelenos that rely on it into a deeper state of uncertainty.

San Diego recently shifted much of its supply off LA. In 1991, the Water Authority bought 95 percent of its water from Metropolitan Water District which included that northern California water mix. Today San Diego buys just 13 percent of its supply from Los Angeles.

But whether San Diego buys its Colorado River water from Imperial Valley or LA directly, San Diego still has to pay LA to use its aqueducts because the region doesn’t have its own pipeline to the river. That’s historically been a recipe for drama. For years, the Water Authority has been fighting in court to lower Metropolitan’s aqueduct-related fees known charged in part to get a portion of Imperial Valley’s allotted river water to San Diego. 

A Straw to San Diego

The reverse osmosis barriers inside the North City Pure Water Facility / File photo by Megan Wood

Every few decades, members of the Water Authority’s governing board resurface the idea of building the region its own pipeline to the Colorado River. The last round was September of 2020 when officials floated building a straw parallel to the one owned by Metropolitan, which would have cost at least $5 billion while not bringing any new water to the region. 

Proponents, though, argued that it would give San Diego control over water infrastructure costs, the primary driver of ever-rising water rates.

Denham said the Water Authority put “its pencils down” on that project for now as inflation, costs of construction and labor continue to rise. Estimates on what it would cost to build the pipeline, Denham said, now are likely much different than even just two years ago, when the board paid a consulting firm just under $2 million to study new routes for the pipe. 

In the meantime, San Diego relies on Imperial Valley’s water supply surviving severe cuts through the latest extreme drought impacting the Colorado River. Allocating Colorado River water relies on a century-old set of agreements and contracts that say Imperial irrigation District is virtually last in line to be cut by force. 

A view of the Colorado River as it flows through northern Arizona / Image via Shutterstock

While a portion of Los Angelenos faced rounds of tight, mandatory water restrictions this year as northern California resources dried up, San Diegans continued watering lawns under light and mostly voluntary restrictions. 

The Water Authority celebrated its “drought-proof” supplies, attributed largely to its deal with Imperial Valley and huge investments in reservoirs for emergency storage, albeit all at an increasingly larger impact on San Diego pocketbooks. 

San Diego is developing more water options as sewage becomes a recyclable commodity in this coastal desert. The City of San Diego is spending billions to recycle its wastewater into drinking water and a collection of East County water agencies are doing the same. But those projects will take years to complete.

Since 1991, when San Diego bought 95 percent of its water from LA and therefore the Colorado River and northern California, San Diego has diversified its sources some. About 10 percent of the region’s drinking water comes from a plant in Carlsbad that de-salts ocean water. Another 5 percent comes from recycled water plus 6 percent from pumping up groundwater and the rest  come from local surface water and a small additional canal lining project on the San Luis Rey River.

The region has a long way to go if the goal were to wean itself off the Colorado River entirely. But the river remains the cheapest source on paper for now. 

Correction: This post has been updated to reflect specifics about how San Diego contracts for Colorado River water.

Join the Conversation


  1. “The Water Authority celebrated its “drought-proof” supplies, attributed largely to its deal with Imperial Valley. . .”

    The Water Authority’s drought proof supplies still rely on the Colorado River. The on going drought in the West means that the Colorado River is no longer a reliable supplier of water. If we want truly “drought proof” supplies the answer is at least two more large Desal Plants, combined with conservation, storage and recycling.

    As noted in the article making us truly water independent will be expensive, but that expense is a fraction of what Water Rationing would cost. LA is on the wrong path, we must divorce ourselves from them or they will impose their restrictions on us. If we become water independent we can tell MWA to “Go Pound Sand.”

  2. I found Ms. Elmer’s article to be confused and downright wrong on several points. In the third paragraph she makes reference to an entity she calls the “Los Angeles Metropolitan Water District.” There is no such entity. The true name of the entity she is referring to is the Metropolitan Water District of Southern California. The in the fourth paragraph Ms. Elmer states: “Increasingly, the region buys its water from the Imperial Valley, instead of Los Angeles.” The region has in fact never purchased water from Los Angeles, whose water is delivered through the Los Angeles Department of Water and Power. Ms. Elmer continues at a half dozen points in the balance of her article to state that LA is supplying and our region is buying water from LA. This is simply false. It’s the Metropolitan Water District, a cooperative consisting of 26 member entities, that sells water to our region. The aforesaid errors reflect sloppy journalism at best, and lost credibility is a hard thing to recover.

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