Why desalination won’t save states that depend on Colorado River water

The Colorado River encircles Horseshoe Bend in Glen Canyon National Recreation Area in Page, Arizona.

Rhona knew | Afp | fake images

States that depend on the drought-stricken Colorado River are increasingly looking to desalination as a way to correct the river deficit and increase water supplies throughout the western US.

The search for alternative ways to get water comes as federal officials they continue to impose mandatory water cutoffs for states that feed from the Colorado River, which supplies water and power to more than 40 million people.

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Desalination (or desalination) is a complicated process that involves filtering the salt content and bacteria from ocean water to produce safe drinking water for the tap. While there are more than a dozen desalination plants in the US, most in California, the existing plants do not have the capacity to replace the amount of water the Colorado River is losing.

“Ocean water desalination has tremendous appeal,” said Robert Glennon, professor emeritus of water law and policy studies at the University of Arizona. “The idea is that if we can get the salt out of the water, everything can be fixed. But it’s a kind of siren song that will turn bad.”

Desalination plants are expensive to operate, require enormous amounts of energy and are difficult to manage in an environmentally friendly way, according to water policy experts.

The debate over whether desalination could be a solution to the drying up of the Colorado River comes as a historic mega-drought grips the western US, spawning the region’s driest two decades. in at least 1,200 years. Water levels in the country’s two largest reservoirs, Lake Mead and Lake Powell, have reached their lowest levels on record.

Pipes containing drinking water are shown at the Poseidon Water desalination plant in Carlsbad, California, USA, on June 22, 2021. Picture taken on June 22, 2021.

mike blake | Reuters

The Biden administration has urged seven Colorado River basin states to save between 2 million and 4 million acre-feet of water, or up to a third of the river’s average flow. But water managers say the savings will need to be much more drastic as drought conditions worsen in the basin.

Kathryn Sorensen, who leads the research at the Kyl Center for Water Policy at Arizona State University, said that while there has been great progress in water conservation across the West, the Colorado River is severely overcommitted and the low levels of the reservoirs are “extremely problematic”.

“We’ve been taking more water from the river than mother nature can really provide,” Sorensen said. “The river is a super important resource for all of us.”

The cost of water is high

Since desalination is a drought-resistant process, some have argued that states with such facilities could become less dependent on water from the Colorado River. But the cost of desalination is high compared to the cost of imported river water, and the process requires a great deal of energy to separate salts and other dissolved solids from the water.

Large-scale plants require “tens of megawatts” to operate, according to the Department of Energy, and energy consumption is the largest component of desalination operating expenses, comprising about 36% of total operating expenses.

For example, the Carlsbad Desalination Plant in San Diego, California requires about 35 megawatts of electricity to run. (For comparison, 1 megawatt is enough power to run a small city, and 1,000 megawatts is enough to power a medium-sized city.) The plant produces an average daily flow of 50 million gallons, only about 10% of the total drinking water needed by San Diego.

The cost of desalinated water in Carlsbad is estimated at $2,725 per acre-foot, according to a recent analysis by environmental economist Michael Hanemann of Arizona State University. That’s significantly more than the amount the San Diego County Water Authority pays for water from the Colorado River and the Sacramento San Joaquin River Delta. Last year, the Water Authority proposed to increase its rate to $1,579 per acre-foot of untreated water in 2023.

“Desalination technology has gotten a lot better and it’s now remotely plausible to do it,” said Jay Lund, co-director of the Center for Watershed Sciences at the University of California, Davis. “But it’s only plausible if you’re willing to pay a lot of money.”

Water policy experts have also long debated the possibility of taking water from Mexico’s Sea of ​​Cortez, the closest sea to Arizona. Indeed, Arizona officials voted in December to advance study of a $5 billion project led by an Israeli company to build a plant to desalinize seawater in Mexico and transport it in a pipeline that would run through Organ National Monument. Pipe Cactus.

The company leading that project said it would deliver up to 1 million acre-feet of water to Arizona, about the amount the central and southern part of the state used from the Colorado River in 2022. The first phase of the plan would be a single pipeline that would transport approximately 300,000 acre-feet of water to Arizona, with future pipelines delivering up to 1 million acre-feet.

If the desalinated water they were going to cost between $2,000 and $3,000 per acre-foot for the Mexico plant, then the cost could potentially run up to nearly $1 billion each year for 300,000 acre-feet of water. And the cost could reach nearly $3 billion per year for 1 million acre-feet of water.

The environmental costs of desalination

There are also environmental costs to desalination. In addition to the greenhouse gas emissions produced by the large amount of energy required to operate, the process leaves excess brine, or concentrated saltwater, which can increase the salinity of seawater and, as a result, harm local marine systems. and the quality of the water.

The brine may contain toxic metals such as mercury, cobalt, copper, iron, zinc, and nickel, as well as pesticides and acids that cause irrevocable changes in the environment.

“It’s hard to bring desalination projects to scale because desalination is extremely expensive and there are real problems disposing of the leftover brine,” Sorensen said.

A study published in the journal ScienceDirect found that brine volumes are greater than most industry estimates, averaging one and a half gallons for every gallon of freshwater produced. The authors recommended brine management strategies that limit negative environmental impacts and reduce the economic cost of disposal.

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However, the current most widespread practice is to dump the excess brine back into the ocean, what has led to the death of fish and coral populations, as well as damage to sea grass and fish larvae.

California regulators last year rejected a $1.4 billion desalination plant in Huntington Beach, citing not only water costs but also dangers to marine life and risks associated with rising sea levels and flooding.

Desalination will be useful in some areas of the country, especially as operating costs come down and more research is done on brine disposal. But water policy experts have suggested alternatives that are currently less expensive and energy intensive and pose no environmental risks.

Lund said low-value fallow farming is a better and cheaper alternative from a national and state perspective, since farming uses about 80% of the Colorado River’s water. “It’s the cheapest and most sustainable way to restore balance to the system,” Lund said.

Wastewater reuse, water conservation and encouraging water reallocation are other sustainable solutions to water scarcity that should take precedence over desalination, Glennon said.

“Desalination is not a silver bullet. There are immense challenges,” Glennon said. “We can do it, there’s no question about that, but it’s not the only option.”

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