San Diego temporarily solved its water crisis by turning ocean water into fresh water. But desalination won't work everywhere.

• The largest desalination plant in the US is in San Diego.
• Experts have said the huge costs and ecological risks mean these plants might not work nationwide.
• Other options, such as water recycling and conservation efforts, might be better.

In the early 1990s, San Diego was dying on the vine, starved of water in a series of yearslong droughts.

The county, which relied almost entirely on imported water, had to cut back on 30% of its usage and was at risk of losing 50%. 

At the last minute, a miracle saved San Diego — rain and snow in the desert replenished aquifers, saving the city from intense cutbacks.

But the water didn't extinguish the passion of San Diegans, who after finding themselves in this situation, rallied together to find a way to become more self-sufficient, Jeremy Crutchfield, the water-resources manager at the San Diego County Water Authority, told Insider.

Enter the Claude "Bud" Lewis Carlsbad Desalination Plant. It would become the largest facility for turning salt water into fresh water in the United States. Now, about 10% of the county's water comes from that plant.

It's not the only way that San Diegans get their water, but it's another tool in their kit to make sure drought would never threaten them again, Crutchfield said. 

"We've proven here in San Diego that it works," he said. 

But San Diego got lucky. Water access is threatened across the US, from a six-way tug-of-war on the fraying rope that is the Colorado River's water supply, to engineers' 24/7 efforts to prevent salt water from seeping up the Mississippi River.

But for other cities, desalination might not be the answer.

What is desalination, and how is San Diego using it?

Desalination works by taking salty water and running it through a series of increasingly fine strainers to remove debris. It's then pushed through a membrane with tiny holes that capture the salt while fresh water flows through.

The holes in the membrane are about 0.1 micrometer in diameter — 1,000 times thinner than a sheet of paper.

Just to push the water through such a small membrane, you need "a heck of a lot of electricity," Robert Glennon, a professor emeritus at the University of Arizona and the author of "Unquenchable: America's Water Crisis and What to Do About It," told Insider.

All that electricity costs a lot of money.

Each day, the plant generates 50 million gallons of fresh water for San Diego County, which over the course of a year amounts to between an estimated $49 million and $54 million in operations costs, a 2017 article in The Wall Street Journal said.

The water-treatment facility in Orange County, California, which purifies highly treated sewer water into drinking water and serves a similar-sized population, costs about the same — $50 million — to operate each year. Except it generates about 3 ½ times more water than Carlsbad, meeting about 35% of Orange County's water demands.

Both plants cost between around $900 million to $1 billion to build.

All together, desalination costs more money than most local governments are willing or able to spend on their own, Frank Ward, a professor of resource and welfare economics who studies water policy at New Mexico State University, told Insider.

Ward said, "the grim specter of costs that always comes to bite us in the rear, doesn't it?"

But when stars align 

On its own, San Diego County probably wouldn't have had the funds to get the Carlsbad plant up and running, Crutchfield said.

But there was enough public interest in water resources in the area at the time to get the attention of a private player — Poseidon Water LLC.

In 1998, Poseidon agreed to front the funding, permitting, designing, constructing, and early operating costs, using company funds and public-activity bonds. The company took on a huge amount of early risk, Michelle Peters, director of operations at Poseidon, told Insider. 

One of the reasons Poseidon got the plant approved was because it had found a location that made it easy to access water, which helped it sidestep backlash from local environmentalists.

Normally, where a desalination plant gets its salt water from and where it dumps its wastewater is of major environmental concern. Sucking the water in means sucking any tiny or microbial life that could disrupt the ecological balance in with it.

Then dumping dense, salty waste back can drastically change the ocean's salinity and suffocate marine life, Michael Hanemann, a professor of water economics and policy at Arizona State University, said.

These concerns troubled Glennon enough that when he was asked to consult on a new desalination proposal in the Salton Sea in California, he recommended against it. He remembered thinking, "What would we be doing, taking this virgin piece of beach, a functioning ecosystem, and completely degrading it?"

But the Carlsbad plant was built next to a power plant conveniently located on the shoreline.The power plant used ocean water to cool its machinery — so the desalination plant could use that hot saltwater waste for its main supply. 

One person's trash is another's treasure, as they say.

Since Carlsbad was using water that was being extracted anyway, it posed no additional threat to the ecosystem — at least on the front end. But it did have to address the back end.

Peters said they developed a method of diluting the brine before sending it back to the shoreline by a discharge pond. In the eight years since it began running, the plant has kept salinity levels within regulations the California Ocean Plan Amendments has set, so in that regard, the method worked, Peters said.

Moreover, dilution can be an effective way of managing environmental impact, Glennon said. 

The other options for saving water

Because of building and operations costs, plus their potential environmental and ecological toll, desalination plants might not be the saving grace to the country's water crisis that people might think, Glennon said. But they can be a backup plan.

"As an economist, in principle, there is a case for desal as a form of insurance against disruption of conventional surface-water supply," Hanemann said.

But there are far easier methods to consider as the first line of defense against water shortages, such as conserving water, recycling used water, and manipulating the cost of water, Glennon said. When applied rigorously, these methods have been promising in the past.

In 2019, Los Angeles proposed recycling water from sinks, showers, toilets, appliances, and machinery into its water supply. Recycling this source would make enough drinking water a year to equal the seventh-largest river in the United States, the Columbia River, Glennon said. 

With these easier options on the table, it's even more staggering that cities such as San Diego have pushed desalination efforts through.

Peters recognized that her company's success in San Diego might be a rare occurrence.

When it comes to using desalination in other cities across the country, she said, "I'm sure anything could be done. But whether that's the right call is going to be very dependent on where you're looking at."

Roughly 200 desalination plants are currently operating in the US and about 50 to 75 new projects are proposed each year in the country.