In an age when freshwater supplies are under pressure from a growing human population, the alchemic act of turning seawater into drinking water is enormously appealing.
Gov. Jerry Brown has proposed two giant tunnels, each wide enough to contain most of the Sacramento River, to alleviate California’s chronic water woes and reduce tension between San Joaquin Valley farmers and salmon advocates. This controversial project, billed “California WaterFix,” is little more than a modern application of irrigation technology developed by the Roman Empire.
Scientists at an East Bay laboratory, meanwhile, are also trying to address water shortages, but to do so, they’re delving into uncharted realms of science and technology.
Like Brown’s clunky tunnels, the scientists’ lab-scale project involves passing water through expensive tubes—but the water conveyance tunnels being assessed by researcher Aleksandr Noy and his colleagues are barely one atom wide.
Noy works at the Lawrence Livermore National Laboratory, where he has spent almost 20 years studying the potential of tiny carbon nanotubes—50,000 times thinner than a human hair—to separate salt from water. Noy drew attention from the research community last August when he and several colleagues published findings that using a thinner nanotube greatly increases the rate at which water can pass through a desalination filter.
“Imagine you have a group of people going through a door, and they all bump into each other as they go through one by one,” Noy says.
Well, it turns out that using a thinner tube facilitates a smoother, albeit single-file, flow.
“It’s like all those people form a chain and hold hands, and that way they can slip through the doorway much faster.”
As with polymer membranes, currently employed by desalination plants worldwide, the salt molecules are too wide to pass through, and freshwater flows out the other side—but huge implications dwell in the details. In Noy’s recent experiments, saltwater has passed through the nanotubes six times faster, using 25 percent less energy than it would to pass through desal systems now in use.
Noy says future nanotube systems, in the very best of scenarios, might be able to desalinate seawater hundreds of times faster than existing ones.
In an age when freshwater supplies, both in California and abroad, are under pressure from a growing human population, the alchemic act of turning seawater into drinking water is enormously appealing.
“It’s an understandable perspective when you look west from California and see all that water,” says Jonas Minton, a Sacramento-based water policy advisor for the Planning and Conservation League.
But Minton, who chaired a state-advising desalination task force in the early 2000s, thinks desalination of seawater should be a last resort for California. That’s because it comes with problems: Pumping water from the ocean can harm marine life, and so can discharging the brine that contains the salt removed from the fresh stuff. The enormous amount of energy needed to squeeze salt out of water also makes desalinated seawater almost prohibitively expensive, and a source of greenhouse gas emissions.
“It’s generally two or three times as expensive as alternative water supplies,” says Jay Lund, a UC Davis professor with the Center for Watershed Sciences.
But Peter Fiske, director of Lawrence Berkeley National Laboratory’s Water–Energy Resilience Institute, says the energy costs of desalination should not be a deal breaker, and that it must play a role in supplying the state with water.
“Desalinating seawater does take a lot of energy, but there are lots of valuable things in our society that take a lot of energy,” he says.
California is home to several seawater desalination facilities, with at least one very large facility being planned.
There’s no question California has cheaper, safer options for producing water. Heather Cooley, water program director at the Pacific Institute, says the state’s urban population could produce at least 4 million acre-feet of water each year—80 times the amount now coming from seawater desalination statewide—simply by using less water to begin with. Recycling treated wastewater that flows out to sea could produce, some say, another million acre-feet.
In fact, Noy has speculated that carbon nanotube filtration systems might wind up serving water recycling systems, if not desalination plants, though he says any commercialization of the technology is at least five years off.
California just experienced its hottest recorded summer, with all-time heat records logged in numerous cities, biggest-ever wildfires and—in early January—a record-breaking rainfall day in downtown Sacramento. The turbulent year came after the worst drought in an estimated 500 years or more. Clearly, the scientific consensus that climate change will cause increasingly variable weather and extreme conditions is coming true—and this will certainly impact the state’s water supply.
Still, Lund is open-minded but conservative when it comes to developing desalination. He thinks California’s climate must grow dramatically drier, and water much more expensive, before seawater desalination becomes financially viable at large scales. For now, the technology remains on the fringe of feasibility.
“Desalination is a promising tool,” Lund says, cracking a subtle joke, “and it probably always will be.”
Two decades of R&D
In the Zucker brothers' 1984 comedy film Top Secret, fictional rock star Nick Rivers, imprisoned in Cold War Germany, breaks out of his cell, scurries through the bowels of a prison and abruptly tumbles out of a ventilation duct into an underground laboratory. The musician is greeted by a scientist, clad in a white lab coat, who tells him he had spent years developing “the first magnetic desalinization process so revolutionary it was capable of removing the salt from over 500 million gallons of seawater a day.”
“Do you realize what that could mean to the starving nations of the Earth?” the scientist asks.
Rivers, played by a bright-faced 25-year-old Val Kilmer, answers, “Wow–they’d have enough salt to last forever.”
The entrance to Noy’s lab is a bit more formal, requiring an escort from the gate and a brief glance from an armed guard in camo fatigues. Once inside, Noy himself is careful about making grand claims about what his work may accomplish.
“We don’t want to embellish what we are doing here,” he says as we walk through the maze-like, institutional-gray halls of the facility.
Noy, who speaks with a faint accent from his native Russia, took his current post at Lawrence Livermore in 1998. Though the esteemed facility’s main focus is nuclear weapons, the science of desalinating water has absorbed Noy’s attention here for 19 years. In the early 2000s, he and several competing scientists from other institutions made advances on the nanotube desalination front. They were, as he says, “in a friendly race,” and it was Noy’s lab that broke ahead in 2006, when a test batch of saltwater ran through a nanotube system so quickly that freshwater overflowed the capture basin overnight. Noy says the water had moved through the filter thousands of times faster than he’d expected it to.
More than a decade later, Noy and several colleagues and assistants still work in the same lab.
“Have you been to a water treatment plant before?” he asks, still leading me toward his office.
I have—the Silicon Valley water treatment plant, which uses polymer membranes to filter impurities and trace salts from urban wastewater.
“We are nothing like that,” he says.
It’s true. The focus of his work—still some of the world’s most groundbreaking nanotube filtration research—is still confined to the desktop scale. Noy’s lab is crammed with beakers, test tubes, vials of solution, vacuum chambers, computer screens and powerful microscopes. Noy guesses it will be five years, at the very least, before the technology he is working on moves to a commercial scale.
Though he is modest, Noy is also bluntly honest about his work.
“In principle, if you made a membrane that uses the same mechanism as we’ve been studying, you could move water through 100 to 200 times faster,” he says.
The reason these nanotubes work so much more effectively at filtering water has to do with the carbon atoms they’re made of. Industry-standard polymer-filtration membranes contain proteins called aquaporins that may be attracted to hydrogen, ultimately slowing the passage of water through a filter. But carbon is hydrophobic, Noy explains. This has the effect of causing the water molecules, just before they enter the tubes, to align themselves in a smoothly flowing, single-file chain. There is little or no friction between the water and the tube walls, and the H2O molecules zip through the filter.
It sounds brilliant, but in the world of separating salt from water, efficiency doesn’t come for free. Noy says a big problem with rapid desalination is clearing the salt off the filtering membrane.
“We don’t know if we could actually use the membrane at that speed,” Noy says. “If you pass water through that fast, salt will begin to build up at the surface—like a salt traffic jam. So, where will that salt go?”
He says the filtered salt can actually crystallize over the membrane, effectively clogging it.
“So, even though you have this built-in advantage of really high flux, it doesn’t mean you should necessarily run it at that flux.”
Years of experimenting lie ahead, in which time Noy and his colleagues must try and understand the mechanisms and efficiencies of nanotube filtration and, based on their findings, optimize the filters and size the nanotubes specifically to target certain particles.
“With nanotubes, we actually have a chance to make a membrane that is selective only for water,” Noy says.
That would be the gold-standard filter, preventing everything except water molecules passing through. Polymer membranes, with their much wider tubes, may prevent salt from passing through a filter, but they allow various harmful particulates, like pharmaceutical pollution and endocrine disruptors, to pass through.
Noy explains that another massive challenge in desalination, energy demands, can also be streamlined, but only to a point. The absolute minimum of energy needed to desalinate Pacific Ocean water at a recovery rate of 50 percent of the inflow volume—the optimal rate in terms of energy requirements, since the saltier water gets, the harder it is to desalinate—is roughly 3.8 kilowatt hours per 1,000 gallons of water. (An electric motor rated at 1,000 kilowatts, running for one hour, uses 1 kilowatt hour of energy.)
“Anything less than that number would violate the laws of physics,” Noy says, explaining that this figure corresponds to the osmotic pressure needed to separate the molecules.
It takes 4,888 kilowatt hours to desalinate an acre-foot of water, 3,900 to deliver an acre-foot from the Sacramento-San Joaquin River Delta and 385 to recycle an acre-foot, a 2016 study calculated. Emissions in CO2 equivalents, according to the authors, ranged by equal proportions, with recycled water producing one-twelfth the CO2 equivalents of desalinated water.
Noy says carbon nanotubes could reduce energy inputs into seawater desalination by 25 percent.
“That’s a lot when you consider the amount of energy being used,” he says.
An acre-foot of desalinated seawater in California costs $2,000 to $3,000, according to a 2016 report titled “Proceed with Caution.” The same amount of water—326,000 gallons, about the average Californian household’s one-year supply—costs anywhere from $300 to $1,300 when produced through recycling. And simple conservation can make available an acre-foot of water for as little as $300 or less.
The Silicon Valley Advanced Water Purification Center, in San Jose, treats and recycles 8 million gallons of water per day, directing it toward uses other than drinking water—mostly urban landscaping. Hossein Ashktorab, the plant’s recycled water manager, says the facility has considered investing in desalination but, for cost and logistical reasons, opted against it.
“We’ve compared desalination to water reuse, and water reuse is much better—it’s more cost effective and more environmentally friendly,” he says. “So, in the next 20 to 40 years, we’re concentrating our focus on wastewater and purifying for reuse.”
Scientists elsewhere are working to address serious environmental threats associated with desalination. To mitigate the risk of entrapping of larval sea creatures, many modern plants are being built with their intake pipes buried deep in the sand, sometimes in the form of wells drilled into beaches between the high-tide and low-tide zones.
To deal with the harm of the extra salty effluent, many desalination plants blend their brine with effluent from wastewater treatment plants, or discharge the brine from multiple small pipes angled upward in a way that promotes mixing with surrounding seawater.
In theory, such mitigations, combined with the use of solar panels or other renewable energy sources to run the plants, could take care of most of the environmental issues.
Newsha Ajami, Stanford University’s director of urban water policy, believes desalination should be kept on the table as an option, especially in parts of the world with no better option for accessing freshwater. However, in much of California, she feels it must be considered a last resort.
“It’s a very expensive solution, and it’s very energy intensive,” she says. “If there are cheaper, better, more environmentally friendly solutions at the table, why wouldn’t you use them?”
In the late 1980s, a severe drought drove California into a water crisis. The dry spell would last six years, depleting reservoirs and prompting aggressive conservation efforts statewide. The city of Santa Barbara did more than that, electing to invest in a $34 million desalination plant. The project went online in March of 1992.
Just three months later, it shut down. The next winter was a wet one, and as depleted reservoirs refilled, Santa Barbara’s desalination plant remained idle. For more than 20 years it stayed that way, and for desalination skeptics, the plant stood as an example of why such facilities should not be built in the first place.
“The drought ended, and they had much cheaper options for producing water,” Cooley says. “That was a significant capital investment for the community.”
However, in the midst of another drought in 2015, the Santa Barbara City Council voted to reopen the plant. It reopened in May of last year, and once fully operational will provide Santa Barbara residents with 30 percent of their potable water.
Another potential lesson in desalination economics comes from Australia, where a 12-year dry spell parched the nation and finally ended in 2010. To buffer its water supply, the nation built six desalination plants at a cost of more than $10 billion. A wetter climate cycle resumed, and nearly all the plants shut down within a few years of opening.
“Now only one is still operating,” Lund says. “They were too expensive to operate.”
In spite of challenges in desalinating water and doing so cost competitively, the industry is growing. Globally, 18,000 desalination facilities were operating as of December 2015, according to the International Water Association, producing about 1 percent of the world’s drinking water. In places such as Israel, Dubai and Singapore, desalination projects have proven very cost effective, mainly because so little other water is available.
In California, seawater desalination plants have been built in several locations, including Catalina Island, Santa Barbara and Carlsbad, near San Diego, to supply communities with freshwater. Another desal project is underway in Monterey, although it is facing a legal challenge.
Like the proposed Monterey facility, about two dozen plants are desalinating brackish groundwater. This takes less energy. However, there is relatively little brackish groundwater available to work with.
Minton, at the Planning and Conservation League, says California aquifers contain about 100,000 acre-feet of brackish groundwater that could be desalinated at a fraction the cost of desalting seawater.
The Carlsbad plant, built by Poseidon Water between 2012 and 2015, is the state’s largest. Former Sen. Barbara Boxer recently wrote an editorial for the San Diego Union-Tribune in which she praised the facility.
“The plant in Carlsbad serves as a shining example of the advances that have been made in pursuit of safe, reliable climate change-resilient water,” wrote Boxer, who is a paid lobbyist for Poseidon.
The Claude “Bud” Lewis Carlsbad Desalination Plant is located beside the Encina Power Station, where it will share the existing facility’s seawater intake pipe—which the power plant needs for cooling off machinery. The desalination plant will similarly share the power station’s outfall pipe. To conserve energy, the desalination plant uses 144 energy recovery devices produced by the aptly named Energy Recovery, Inc., in San Leandro. These contraptions capture the hydraulic energy contained within the high-pressure outflow stream of discharged brine and uses that energy to help operate the intake pumps. The plant’s website claims this saves 146 million kilowatt-hours of energy per year and reduces annual carbon emissions by 42,000 metric tons. The facility, which produces as much as 50 million gallons of drinking water per day, will also be restoring 55 acres of wetland.
But to Minton and other desalination skeptics, the Carlsbad facility shows why communities should avoid seawater desalination. The facility went online in December 2015 and in the 2016-17 year produced 40,000 acre-feet of freshwater. This wound up being an oversupply of water, thanks to last winter’s heavy rains. Since the plant is operating on a contract that requires the San Diego County Water Authority to buy the desalinated water whether it needs it or not, the agency poured more than half a billion gallons of desalinated water into a reservoir, where—to be used again—it must undergo standard treatment processes.
David Zetland, a water policy analyst and author who studied at UC Davis and now lives in Amsterdam, says the plant is a complete waste. “They didn’t need it, because consumers have reduced their demand enough to live with conventional supplies.”
Now, Poseidon Water is proposing to build another desalination plant in Huntington Beach. It is being promoted as state-of-the-art, with energy recapture systems to improve efficiency and systems in place that will minimize marine impacts. In a San Diego Union Tribune editorial, Boxer says the Huntington Beach plant will be “the most environmentally sound desalination plant in the world.” Opponents “are behaving like climate change deniers” by ignoring science, the politican-turned-lobbyist wrote.
John Kennedy, the Orange County Water District’s executive director of engineering and water resources, says even injecting the water into the ground would serve a good purpose, helping guard against seawater intrusion into the local aquifer. While all the desalinated water might not be needed immediately by the local community, he says having the plant will be a good security measure.
“We don’t know how much imported water will be available in the future,” he says. “Exports from the Sacramento-San Joaquin Delta keep getting cut lower and lower, and who knows if they’ll ever build the tunnels.”
Kennedy says the desalination plant will increase local monthly water bills between $3 and $6 per month.
“That’s not very much, and it’s a good insurance policy, if nothing else,” he says. “Poseidon has come along and offered to build us a desalination plant in our backyard, and if we say no now, we might not get another chance.”
Fiske, at the Lawrence Berkeley lab, says the cost of desalination, and the energy needs, are rather trivial compared to its potential value. The ocean, he says, cannot be overlooked as a water supply for coastal communities in arid places, primarily for the obvious reason—the ocean is essentially endless.
“Ocean desalination represents a water supply that has very, very limited risk—we’re always going to have ocean water to treat and purify,” he says.
Fiske believes every coastal community in California without a highly reliable water supply should aim to use seawater desalination to produce between 7 and 10 percent of its supply.
“Ocean desalination doesn’t have to be a large percentage of our water supply, but it provides a very stable, very reliable source,” Fiske says. “I like to think of it a little bit like a portfolio. You have some assets that have low cost but are variable, and you want to also have some assets that might be higher in cost but are absolutely reliable.”
Like Fiske, Seth Siegel feels the costs of desalination should not be seen as a deal breaker. Siegel, author of Let There Be Water, a New York Times bestseller about Israel’s high-tech path toward water sustainability, says the energy needed to desalinate enough seawater to provide a family of four with all their household needs is the electricity equivalent of having a second refrigerator.
“We all have refrigerators, and televisions, and nobody is saying we shouldn’t because of the energy costs,” he says. “We don’t tell people they should go back to a lifestyle of the ’60s and ’70s.” He argues that desalination, while not appropriate in regions with consistent rainfall, may be a vital technology of the future, especially in affluent areas that can afford to pay for it and where water is in short supply.
“We shouldn’t rush into it, because they’re expensive to build, but we also shouldn’t be ideological about it and say we shouldn’t desalinate water because it takes energy,” he says.
Urban Californians, whipped into shape by repeated droughts, are using less and less water each year. In 2010, the Sacramento Suburban Water District was serving 170,000 people. Now, its service population is 177,000. However, overall water use has plunged, according to data provided by Roscoe, from 12.3 billion gallons in 2010 to 5.8 billion in the water-year ending in 2017. That corresponds to a per capita reduction from 199 gallons per day to just 90. A similar drop has occurred in San Francisco, where a rapidly rising population is consuming about 20 percent less water than it was in 2005. The city's residents use just 44 gallons per day on average.
The cutbacks have come largely from standardizing more efficient toilets and shower heads, and by removing lawns and making irrigation more efficient—and there is certainly more room to improve. For instance, the Orange County residents who would receive water from the proposed Huntington Beach plant use two to three times as much water as do residents of San Francisco, according to data from the California Department of Water Resources.
Cooley, at the Pacific Institute, says California’s annual urban water use of about 9 million acre-feet could be cut by at least half through further conservation efforts. That, at very little cost, would free up roughly 5 million acre-feet of water per year—enough water to fill a skyscraper 200 miles tall, and about the amount exported from the Sacramento-San Joaquin River Delta each year.
It would take the Carlsbad desalination unit 100 years to squeeze out that much freshwater.
Cooley says stormwater capture could produce another 400,000 acre-feet each year, and water recycling another 1 million acre-feet. In fact, while large cities lobby constantly for more imported water from depleted rivers, coastal water treatment plants discharge almost 1.5 million acre-feet of treated sewage water every year, according to the Department of Water Resources. The Los Angeles area, which annually uses as much as 1.9 million acre-feet of water from the beleaguered Sacramento-San Joaquin River Delta, recycles just 11 percent of its effluent.
Israel, by contrast, recycles and reuses almost 90 percent of its sewage water, and per capita usage is very low—only 40 gallons per person daily. Israel also desalinates lots of water—enough to supply its 8 million people with more than 90 percent of their household needs.
“But they made those investments [in conservation and recycling] first, before they went to desalination,” Cooley says.
Fiske points out that water recycling is not itself a source of water. Indeed, he says, recycling and reusing become less effective the less water a community has available. California’s population is rising and may reach 50 million in 30 years, and its water supply is growing unstable. Total precipitation may decline in the future, and higher temperatures will mean more of it falls as rain, rather than snow—historically the state’s most important storage reservoir. Fiske says to delay desalination development could even risk disaster.
“In Australia, their drought was an economic catastrophe,” Fiske says. “So, we have to ask ourselves, ’What are the consequences of having an extreme drought where we literally run out of water?’”
Nanotubes for recycling?
At Lawrence Livermore lab, it isn't clear that carbon nanotubes will ever produce water at a commercial scale. Years of experimenting lie ahead, in which time Noy and his colleagues must try and understand the mechanisms and efficiencies of nanotube filtration and, based on their findings, optimize the filters and size the nanotubes specifically to target certain particles.
“With nanotubes, we actually have a chance to make a membrane that is selective only for water,” Noy says. Noy believes nanotube filtration technology could eventually find a functional home in water recycling systems, if not desalination.
“It depends what they have in the water that they want to remove,” Noy says. “If they have large-sized impurities, then the carbon nanotubes would be overkill. But if we’re interested in molecules in the water, then this would be a proper use.”
But commercializing the technology could be challenging. Fiske, who is familiar with but not involved in Noy’s research, explains that a garbage can-sized piece of industrial-sized piping that draws water through a desalination system contains 500 square meters of membrane, which is fitted in the system rather like a rolled-up carpet.
“So, any membrane technology needs to be massively scaleable” at affordable costs, he says.
Elsewhere, many researchers are exploring ways to potentially improve the science of turning saltwater into freshwater. A lab at UC Berkeley, for example, is studying the way that tropical mangrove trees process seawater, removing its salt and making it physiologically serviceable. These plants are of particular academic interest because they achieve what the most advanced desalination plants cannot—solar-powered, 100-percent recovery of desalinated seawater.
California is a fitting place for such research. The state has emerged in recent years as a poster-child for the worst of what climate change may deliver—unpredictable weather extremes, fires punctuated by flooding, and the sporadic ebb and flow of water. Amid such inconsistent rhythms, the steady clockwork-like drone of desalination plants—and the prospect of entirely drought-proof water—may eventually resonate even with skeptics. And for desalination believers, it is already clear that California has enough water to last forever.