Resources

Many people had to be evacuated following flooding caused by the destruction of the Kakhovka dam in Ukraine.Credit: ZUMA Press, Inc./Alamy Stock Photo

Oleksandra Shumilova was hundreds of kilometres away from her native Ukraine when, in early 2022, Russian troops invaded and destroyed a water pipeline near her hometown of Mykolaiv. For 24 days, the taps ran dry. When the water finally returned it was contaminated with salt and harmful chemical deposits that rendered it unsafe for drinking.The incident struck a chord with Shumilova, a freshwater ecologist at the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Berlin — on multiple levels. Not only was Mykolaiv her hometown, but she studies the floodplains of a river in Italy that still bear the scars of the First World War.Pockmarked by craters from decades-old aerial bombardments, the area around the Italian river is scattered with unexploded military ordnance. When discovered, these munitions must undergo controlled detonations, creating blasts that reverberate in Shumilova’s mind during her fieldwork.“Remnants of war can stay in nature for a long time,” Shumilova says. Now, she fears, history is repeating itself in the Russia–Ukraine war.Shumilova took it upon herself to chronicle what is happening in Ukraine. “This research is very personal,” she says. She began poring over government records and media reports, meticulously searching for instances of damage to water resources and infrastructure, resulting from military actions. She and her collaborators cross-checked their findings with information from a diverse array of Ukrainian, Russian and international sources.

Parts of Kherson, Ukraine, were flooded after the Kakhovka dam was destroyed during the Russia–Ukraine war.Credit: Roman Pilipey/Getty Images

Focusing on just the first three months of the conflict, a detailed record of 64 events emerged, each affecting crucial water facilities and often triggering a chain of events1. Missiles striking hydropower dams, for example, might result in power outages that render water-pumping stations and wastewater treatment facilities inoperable — with devastating consequences. Millions of people can be left without access to clean water, agricultural fields might have insufficient irrigation, and the unchecked flow of untreated sewage and contaminated ground water from industrial mines can pollute nearby river basins, causing significant harm to both people and the environment.These incidents highlight just one aspect of the intricate interplay between water and armed conflicts. Water resources can be casualties of violence, but disputes over water control can also act as triggers for unrest — for example, when two communities clash over access to a single water source. Furthermore, water is frequently weaponized, as has happened in Gaza, when Israel responded to the deadly attacks by Hamas on 7 October by restricting access to fresh water and cutting off fuel shipments needed to run desalination and water-treatment plants for local production of potable water.Historical records show that conflicts over water access stretch back millennia, with water systems often being targeted or manipulated as strategic assets on the battlefield. But this water–war nexus seems to be intensifying. Driven by escalating tensions and intensified hostilities in places such as the Middle East, Ukraine, southern Asia and the Sahel region of sub-Saharan Africa, water resources have increasingly become targets or triggers of violence over the past decade, notes environmental scientist Morgan Shimabuku.“What we do see right now is a really large increase in the total number of water-related conflicts around the globe,” says Shimabuku who is at the non-profit organization the Pacific Institute in Oakland, California, and helped to develop an online database of water-related clashes called the Water Conflict Chronology. There were more than 200 incidents in 2022 alone, and with the ongoing conflicts in Ukraine and Gaza, 2023 is projected to surpass that figure (see ‘Warring over water’).

Source: Adapted from O. Shumilova et al. Nature Sustain. 6, 578–586 (2023)

Add in the mounting stresses on water systems from population growth and climate change, and the potential for violence and instability is only expected to grow. Shimabuku thinks that there is an urgent need for comprehensive and cooperative efforts to safeguard water resources and to promote peace, but she also sees reasons to be hopeful.For example, many previously conflicting factions are embracing collaborative water-sharing treaties, which can de-escalate hostilities. “We have a lot more tools in our toolbox now for addressing these challenges,” Shimabuku points out.Troubled watersIn 1995, the then-vice-president of the World Bank, Ismail Serageldin, made a dire warning for the years ahead: “Many of the wars in this century were about oil, but wars of the next century will be over water.”

People queue to refill drinking water in Mykolaiv, Ukraine, after Russian forces cut off the pipeline used to supply water.Credit: AP Photo/Emilio Morenatti/Alamy Stock Photo

It’s an oft-repeated idea that persists to this day, cited frequently in discussions about water scarcity and conflict. But according to Jampel Dell’Angelo, who studies governance and disputes over freshwater resources at the Vrije University Amsterdam Institute for Environmental Studies in the Netherlands, “this is a myth”. At least when thinking about conflicts between nations.In a globalized economy of countries interconnected by trade, including that of agricultural commodities that can be considered a form of virtual water transfer, tensions over cross-border issues of water scarcity are often diffused by forms of interstate cooperation. This typically prevents water from serving as a trigger for major wars, but it doesn’t stop localized violence from arising in water-strapped nations.In Iraq, for example, large-scale protests over tainted water supplies have been met with strong police crackdowns. Frequent droughts in Somalia have prompted herders to abandon their pastoral lifestyles and join militant groups instead. And neighbouring states in India clash every year over their allocated river waters, with demonstrations that often turn violent.What’s more, the very conditions that promote interstate water peace can actually exacerbate water-related instability at the local level. This is particularly evident in water-scarce low-income countries, which frequently export their limited natural resources, amplifying their local water challenges and potentially fuelling smaller-scale conflicts. “There’s a shift in the burden of water scarcity on the heads of people who already suffer from the lack of water,” Dell’Angelo says.Further compounding the problem, foreign agribusiness investors have increasingly acquired vast land holdings in low- and middle-income countries, often at the expense of local communities and appropriating valuable water resources in the process. Termed land or water grabbing, this phenomenon gained momentum after the economic and food crises of 2008 — and, according to Dell’Angelo, the ongoing war in Ukraine is likely to further intensify this trend, owing to reductions in Ukrainian grain exports and heightened concerns about food security. “This will put additional pressure on land and water,” Dell’Angelo says, “with escalating consequences.”One priority of water-security researchers is to prevent similar crises in the future. “We want to put points on a map and show people where water conflict is happening so that we can better apply solutions,” says Samantha Kuzma, a data scientist at the World Resources Institute, an environmental policy and research group in Washington DC.Those efforts begin with prediction. To identify problem hotspots, Kuzma and her colleagues developed an artificial intelligence algorithm called the Global Early Warning Tool. This tool considers a wide range of environmental, economic and social factors. By comparing past trends to present data, it flags regions where water-related issues such as flooding, pollution and scarcity could spell trouble2.Kuzma hopes that the tool will help to inspire localized conflict-mitigation measures when and where they are needed. This could prove instrumental in drought-affected areas such as Ethiopia, where restricted access to potable water might escalate tensions between government forces and armed factions, or in water-scarce regions of Syria that are already marred by conflicts between rival militia groups.Although implementation can be challenging, Kuzma emphasizes that the timely identification of emerging conflicts can streamline the adoption of collective land-use strategies that will ultimately ease tensions. “If we can see water as the security risk that it is — and have more investments going into securing the resource, and managing it sustainably — we should see real impacts on the ground,” she says.Shifting baselinesThe world’s rapidly changing climate could intensify the need for those kinds of water-security intervention. As a team led by Solomon Hsiang, now chief environmental economist at the White House Office of Science and Technology Policy in Washington DC, showed in an influential 2013 analysis, extreme rainfall conditions can be causally linked to an increased risk of violence and civil war3.

Displaced people in Gaza fetch drinking water outside a school.Credit: MAHMUD HAMS/AFP via Getty Images

Such was the case in Syria, where discontent over the government’s handling of a prolonged drought period contributed to uprisings in 2011. This spiralled into a devastating internal war that persists to this day.Yet, perhaps counter-intuitively, as climate extremes become less anomalous and people become accustomed to more frequent water disasters, it’s possible that the number of water-related conflicts will decline, although the severity of such clashes could intensify.That’s what Marc Müller, a water engineer at the Swiss Federal Institute for Aquatic Science and Technology in Dübendorf, and his colleagues found when they modelled the relationship between climate variability and conflict. Because the reference point for ‘normal’ levels of water availability changes, they concluded, so will the threshold at which people are willing to fight4.Water-related conflicts could therefore become fewer and further between. But when they do arise over ever-shrinking water supplies, Müller warns, the hostilities are likely to escalate quickly. “Conflicts will be less often, but worse,” he says.Such predictions offer little consolation to the people of Gaza, who continue to endure shortages of clean water and a sanitation crisis that is facilitating the spread of waterborne diseases.Water challenges are nothing new in the region. Even before the current conflict, extreme overuse of groundwater resources, a lack of large-scale desalination plants and the discharge of mostly untreated sewage all contributed to water scarcities in Gaza. But the situation is now much worse — and with the world’s attention focused on the water crisis, some researchers are hopeful that more will be done to address the problem once the war ends.“There’s going to be a lot of rebuilding necessary after all the destruction,” says David Katz, a water-policy researcher at the University of Haifa, Israel, “and maybe investing in water infrastructure will be something that can galvanize the global community.”As Katz points out, water cooperation helped to pave the way for a peace agreement between Israel and Jordan nearly 30 years ago, and he’s hopeful that the same might be possible in any future détente between the Israeli and Palestinian governments. “Political change opens up new opportunities,” he says. “It could conceivably happen.”Meanwhile, in Ukraine, the dire impact of Russia’s assaults on the nation’s water infrastructure is consistently and relentlessly worsening. This is starkly evident in the catastrophic destruction of the Kakhovka dam and hydroelectric power plant on 6 June 2023. The massive concrete structure crumbled. Trillions of litres of water gushed out, deluging areas downstream. At least 50 people died and thousands lost their homes.In the intervening months, the extent of the damage to communities, agriculture and the environment has become apparent. The Black Sea, into which the flood waters and accompanying sediment poured, became polluted, with a potentially devastating impact on the local marine ecosystem. Vast tracts of flooded land are no longer amenable to farming, crippling the Ukrainian economy, and areas that remain arable will probably have reduced yields without the reservoir there to provide a steady stream of water for irrigation.This could spell trouble for global food supplies, given the dependence by many low-income countries on Ukrainian grain. “It will touch millions of people, not only those living in Ukraine,” says Viktor Vyshnevskyi, a hydrologist at the National Aviation University in Kyiv, who has studied the myriad water-related repercussions of the dam explosion5.This human-caused flood was not without precedent. During the Second World War, in August 1941, the retreating Soviet army destroyed a dam at the northern end of the same reservoir where the Kakhovka dam was later constructed. The goal was to slow the advance of German forces. But the obliteration of the dam resulted in massive downstream flooding that reportedly claimed the lives of thousands of people. The occupying German forces partially restored the hydrotechnical structure, before they too demolished it as the tide of the war shifted back in favour of the Soviets.With history as a sobering backdrop — in Ukraine and beyond — the persistent use of water as both a casualty and a weapon of war remains a looming threat in a world grappling with the chaos of climate change. However, by shedding light on this issue, water scientists aspire to catalyse efforts that can avert future conflicts and ensure the protection of this invaluable resource for generations to come.“We want to provide a resource for other researchers, policy makers and those who can enact solutions around how to prevent violent conflict related to water,” says Shimabuku.“Could there possibly be water-resource management approaches or governance structures that can be put in place to reduce the potential harm that these conflicts drive?” she asks. In a world in which water is both a source of life and strife, the choice between conflict and cooperation will determine our shared future. More

Water-treatment firm Aquagga’s ‘forever’ chemical destruction unit in Fairbanks, Alaska, uses a technique called hydrothermal alkaline treatment.Credit: Gus Millevolte

Selma Thagard watched in astonishment as the indestructible chemicals did the one thing that they shouldn’t do — fall apart.A chemical engineer at Clarkson University in Potsdam, New York, Thagard was developing a plasma reactor for water treatment in 2016 when an environmental-engineer colleague suggested she add chemicals known as PFAS to the water she was testing. These per- and polyfluoroalkyl substances, also commonly referred to as forever chemicals, are made up of chains of carbon and fluorine atoms held together by some of the strongest chemical bonds in nature. They don’t break down naturally, and many decontamination techniques can’t touch them either. The PFAS wouldn’t be destroyed by Thagard’s plasma reactor, her colleague told her, but might act as a useful reference sample.But it didn’t play out that way. In just a few minutes, the chemicals were no more. “When plasma degraded PFAS so rapidly, within minutes, he told me: ‘That’s not right. Nothing can degrade PFAS,’” Thagard says. She ran the test seven or eight more times, and each time the chemicals disappeared.Thousands of variations of PFAS chemicals have been used for decades in a wide variety of products, including food packaging, stain-resistant textiles and firefighting foam. Their widespread use, combined with their inability to break down naturally, means that they have spread to water, soil and wildlife. Thagard’s colleague was studying the accumulation of the chemicals in fish in North America’s Great Lakes, but they are present all around the globe.The substances also accumulate in people, and are thought to contribute to reproductive issues, impaired immune function and even cancer. Over the past two decades, concern about these forever chemicals has grown, leading to the imposition or proposal of regulations to cap their presence in water in the United States, the European Union and the United Kingdom.But ‘forever’ might be a shorter time than previously thought. Scientists, including Thagard, are developing methods to break down PFAS into fluoride and carbon dioxide, which are not dangerous in the small amounts produced. These approaches to degrading the molecules have arisen in the past few years and could become widely available in just a few more. The big questions are where in the water cycle to deploy them, and which method makes the most economic sense.Treatment technologies by themselves won’t completely solve the problem of PFAS pollution. For one thing, the number of possible molecules based on the carbon–fluorine bond is vast, making it difficult to know for certain whether a particular method can tackle each one. “There are new ones being put on the market each year,” says Timothy Strathmann, a civil and environmental engineer at the Colorado School of Mines in Golden. It can also be difficult to measure some of these molecules, especially at low concentrations. The sheer number of possible molecules, plus their stealthiness, are an ongoing challenge, Strathmann says. “This is why we need to also keep up with our ability to detect and sense these chemicals. Because if you don’t know what you’re looking for, you don’t find it.”Electrical zappingThagard’s water-treatment technique relies on electrical discharge plasma1. She puts water contaminated with PFAS in a reactor and pushes bubbles of argon gas through it. The PFAS is attracted to the interface between the water and the bubbles, and rides them to the surface of the water. The atmosphere above the water is also argon — chosen because it has a high density of electrons. High-voltage pulses of electricity flow between electrodes near the surface of the water, knocking electrons loose from the argon atoms and turning the insulating gas into a conducting plasma.

Environmental biochemist Susie Dai is using a fungus to help break down ‘forever’ chemicals.Credit: Michael Miller, Texas A&M AgriLife

The process delivers enough energy to break the carbon–fluorine bonds. If any PFAS is left, it’s at concentrations too low to detect, below the parts-per-billion level. The fluoride and carbon dioxide that are produced from the disintegration of PFAS are absorbed by the water, but in amounts that Thagard says are too small to be concerning. However, the mechanism that causes the bonds to break — something that was never expected to happen — is still unclear. “The science is largely unknown,” she says. “We are doing extensive research from the fundamental side.”Thagard and her colleagues carried out a field test on PFAS-polluted water at Wright–Patterson Air Force Base, outside Dayton, Ohio, in 2019 and showed that they could treat 4 litres of water and reduce the amount of PFAS to below the health-advisory level of the US Environmental Protection Agency in a couple of minutes2. That was using a crude system, she says; an optimized reactor could treat about 40 litres per minute. The US military has been funding research, including Thagard’s work, into cleaning up PFAS because the long-time use of firefighting foams has contaminated many bases.Thagard is chief executive of DMAX Plasma, a start-up firm she founded in Potsdam to commercialize the technology. The start-up has sold small systems to military and industrial customers. Its standard treatment unit, the company says, requires less electricity than most household electric ovens. With some engineering work, Thagard says that the systems could be scaled up to meet the needs of water-treatment plants.Under pressureAnother effort to destroy PFAS is being led by Aquagga, a water-treatment start-up company in Tacoma, Washington, in collaboration with Strathmann. It is using a technique called hydrothermal alkaline treatment (HALT), which involves adding an alkaline substance such as sodium hydroxide to the PFAS and heating it to 350 °C under high pressure (roughly 160 times atmospheric pressure)3. Under these conditions, the hydroxide draws the fluorine to itself and destabilizes the PFAS molecules. Using high-resolution mass spectrometry, the researchers found that after treating a sample of water containing PFAS they had extracted as much fluoride as should have been bound up in the PFAS to begin with — suggesting it had all been broken down.In the absence of destructive technologies, PFAS in water systems has been filtered out and sent to landfill or an incinerator. But even burning doesn’t destroy all the PFAS, which can be spread by smoke or ash from the incinerator or leach out of landfill. Neither process results in the substances being removed from the environment permanently, the way that the destructive approach does.Some sort of filtration or separation process to increase the pollutant-to-water ratio will probably be a step in any PFAS-destructive technology. “You’re not going to treat a million gallons with the destructive process,” Strathmann says. Indeed, the HALT method that Aquagga is developing works with PFAS that has been caught by an activated-carbon filter. So far, the pilot versions can treat only around 4–8 litres of concentrated PFAS per hour, but the company is working to scale that up. It’s taking orders for systems that can treat up to 75 litres per hour and developing ones that will treat nearly 600 litres per hour.Some attempts to destroy PFAS have only succeeded in breaking long-chain molecules into smaller ones with fewer than six carbon atoms. The HALT method seems to be more versatile. “This process applies across the full spectrum, from the very shortest chains, with only one carbon, all the way to the longest chain we’ve tested”, with ten carbon atoms, Strathmann says. That means it should destroy any PFAS, even those that regulatory agencies have not yet listed as of concern4,5.A sound techniqueIn addition to heated chemicals or bright plasma, high-frequency sound waves might also provide the energy needed to break up the molecular chains, by knocking the fluorine atoms loose. Jay Meegoda, a civil and environmental engineer at the New Jersey Institute of Technology in Newark, is among those working on this approach — known as sonolysis. He sends sound waves at a frequency of about 1 megahertz into a concentrated solution of PFAS6. This ultrasound creates bubbles in the water that are only a few nanometres across.Meegoda keeps pouring acoustic energy into the solution until the bubbles become unstable and implode. That releases a burst of energy, raising the temperature of the water that immediately surrounds the bubbles to 5,000 °C for about 10 nanoseconds. Although brief, the heating “is good enough to break all the molecular bonds”, Meegoda says. Everything in the immediate vicinity of the bubble gets broken down to individual atoms, even the water. Hydrogen and oxygen atoms quickly recombine as water. Carbon atoms from the PFAS join with oxygen to become carbon monoxide, and then carbon dioxide. Fluorine atoms form fluoride ions.Meegoda is working with Tetra Tech, an engineering services company in Pasadena, California, and hopes to run a pilot project with his technology in 2024. He expects to see some sort of PFAS degradation technology, whether his own or another, on the market in about two years.Meegoda, Strathmann and Thagard, along with many other researchers, are focused on degrading PFAS at existing water-treatment facilities, where the chemicals would have to be concentrated before destruction. But Michelle Crimi, a civil and environmental engineer and a colleague of Thagard’s at Clarkson, is taking the attack closer to the source. She wants to use a version of sonolysis to handle polluted ground water. Her idea is to build horizontal wells at contaminated areas, such as air-force bases or industrial sites, where there is already a high concentration of PFAS. “We don’t want to treat extremely low concentrations and huge volumes of drinking water indefinitely,” Crimi says. “That’s super expensive.” As the ground water slowly flows through the well — it could take two days to traverse a 46-centimetre well — an ultrasound system hits it with sound waves at frequencies in the mid-kilohertz range7. In the same way as Meegoda’s sonolysis system, the sound waves deliver enough energy to create bubbles in the water and break apart the PFAS molecules. The water would then continue on its natural course, into rivers, lakes or the aquifers that feed more-familiar vertical wells. “Our goal is to stop the contaminated water from reaching the drinking-water wells,” Crimi says.Crimi has co-founded a start-up company — RemWell in Potsdam — to commercialize her technology. She launched a field test in late October at Peterson Space Force Base in Colorado Springs, Colorado, to gather data on how well the system works.Let it rotLeaning towards a more naturalistic approach, Susie Dai, an environmental biochemist at Texas A&M University in College Station, is working on a technique using bioremediation, which relies on living organisms to break down the PFAS. “Bioremediation is typically cheaper than any other chemical or mechanical process, because you have an organism that’s growing by themselves do the work,” she says.Dai starts with maize (corn) stover — the leaves, stalks and cobs that remain after the maize is harvested. She separates its two main components: the cellulose that makes up plant cell walls and fibres, and the lignin that gives the stalks their stiffness. She then modifies the lignin by treating it with polyethylenimine to add functional groups, then mixes it back together with the cellulose to form a fibrous, organic filter material that can catch and hold the PFAS molecules8. Finally, Dai adds a fungus called Irpex lacteus, or white-rot, that commonly grows on fallen trees. The fungus devours the PFAS, using enzymes to break it down into more benign molecules. It also eats the filter material.Dai still needs to measure whether the fungus fully breaks down all of the contaminant and produces pure fluoride, or leaves behind some chains. “I think it’s pretty promising if PFAS are disappearing from the environment,” she says. “It is still important for us to know what the degraded products are, but it’s less important than the removal of the parent molecule.” She is looking for a site where she can test her technology under real-world conditions.Crimi would like to see the producers of PFAS pollution take further steps to shoulder the costs of cleaning up the problem, which tends to disproportionately affect lower-income communities. “It’s tricky with PFAS, because the solutions are really just emerging. There’s still a lot of work to do to really inform what is the most sustainable and cost-effective way to address the big problem,” she says.Still, she’s optimistic that the world won’t be stuck with forever chemicals eternally. “I always say, ‘Forever no more.’” Scaling up the various techniques now under development would turn that hope into a cleaner-water reality. More

Illustration: Sam Falconer

There is an old joke, made famous by the writer David Foster Wallace, in which one fish says to another, “How’s the water?” The second fish replies: “What the hell is water?”That’s more or less the question Nature faced when putting together this collection of articles on the ubiquitous substance on which all life on Earth (not just that of fish) depends. Any attempt to cover the full spectrum of scientific and social issues associated with water is surely doomed to neglect something of importance. But Nature likes a challenge. This supplement is a compendium of intersecting stories that showcase how water affects the sustainability of healthy human civilization.For millennia, the most primal concern about water has been having enough of it. Some argue that too much attention is paid to water supply, and that the real priority should be making do with what is available. Indeed, progress on conservation and efficiency has been impressive — the US economy now needs much less water per dollar of output than in previous decades.But conservation can go only so far. Rivers, wells and artificial reservoirs provide ample supplies for much of the world, but arid regions still struggle. Some researchers in these water-starved regions are turning their attention to the wet sponge that is the planet’s atmosphere. New technologies could extract clean fresh water from thin air, and sharply reduce water scarcity.No matter how abundant the supply, of course, water intended for drinking also needs to be clean and free of contaminants. Among the most pernicious are the ‘forever’ chemicals known as PFAS: chains of carbon and fluorine atoms held together by some of the strongest chemical bonds in nature, and impervious to most attempts to break them down. But engineers are devising various methods to crack them apart and purify PFAS-contaminated water.Although water sustains life, it can also be a threat. Flooding can ravage communities. In a live webcast earlier this month, specialists shared their latest thinking about flood resilience. They painted an alarming picture of the way floods disproportionately affect the world’s poorest populations, even in rich countries, such as the United States. Indeed, 1.8 billion people (22% of world’s population) live in areas at risk of severe flooding — and almost 90% of them are in low- and middle-income countries. Some researchers say that much of the infrastructure put in place to tame waterways is proving inadequate, or even counterproductive. They advocate rethinking how water is handled in the built environment, including re-establishing the abandoned practices of ancient cultures.The danger posed by water is of course increased by climate change. Minimizing its effects will require a large-scale push towards renewable power sources, but these tend to be intermittent, and therefore dependent on technologies to store and transport energy. One leading candidate for renewable power is hydrogen, which can be formed by electrolysing water. However, there is an inherent tension: an economy dependent on hydrogen energy will inevitably consume vast quantities of water. Reducing hydrogen’s water footprint is an important focus as renewable sources become a bigger part of the energy picture.Finally, because of water’s central role in life, it is also a major component of many human conflicts. Wars have been fought over water access. Armies have wielded water as a weapon. But most commonly water is a casualty of war, as has been seen with the destruction of water infrastructure in the Russia–Ukraine war. Those who follow these events closely think that there is an urgent need to identify likely areas of water conflict, and promote greater collaboration between nations on water resources. We all need water to live — not just fish.We are pleased to acknowledge the financial support of the FII Institute in producing this Outlook and the associated webcast. As always, Nature retains sole responsibility for all editorial content. More

Solar power is the cheapest source of renewable energy available to produce hydrogen.Credit: Timothy Hearsum/Getty Images

To steer economies away from fossil fuels and to cut carbon emissions, hydrogen needs to be produced from low-carbon energy sources, such as wind and solar power. This green hydrogen is particularly attractive to certain big-energy users such as the shipping, aviation and steel industries, which would struggle to run on batteries or plug into renewable energy directly through power grids. And producing hydrogen is straightforward: electricity zapped into water splits the H2O molecules into hydrogen and oxygen, which bubble off as gaseous H2 and O2. The hydrogen can then be piped to where energy is needed.In a world of growing water stress, however, the process’s reliance on water is raising alarm (see ‘Watering the power plant’). Earlier this year, the non-governmental organization Food & Water Watch in Washington DC warned that, by 2050, hydrogen production could gulp down as much water as is used by 34 million US citizens each year. A spate of studies over the past few years provides a more positive picture, however, presenting evidence that scaling up hydrogen production need not threaten water supplies. “Water withdrawals for hydrogen production are negligible compared to total water withdrawals,” says Lorenzo Rosa, an environmental engineer who specializes in links between water, energy and food at the Carnegie Institution for Science in Palo Alto, California.

Source: E. Grubert. Clean. Prod. Lett. 4, 100037 (2023).

Still, Rosa says that water considerations should shape how and where hydrogen is produced, especially because heat and altered precipitation driven by climate change are tightening pressure on water supplies. “Hydrogen’s water consumption is small compared to what’s currently used in fossil-energy conversion and inconsequential compared to agricultural water use,” says Jack Brouwer, director of the Clean Energy Institute at the University of California, Irvine. “But there are serious water availability and delivery challenges at the local and regional levels that will need to be considered.”Brouwer and Rosa say that expanding hydrogen-production technologies and water-treatment options could enable hydrogen producers to tap into a range of non-potable water resources — including seawater — or to slash their water consumption. At the same time, geospatial analyses that maps water and renewable-energy resources against projected hydrogen production and demand can pinpoint where investing in water-saving technology — or deciding to import rather than produce hydrogen — will be key to minimizing tension between the push for hydrogen and the need to preserve water resources.A thirsty processThe water requirements for producing hydrogen by electrolysis begin with a simple calculation: every kilogram of H2 molecules requires 9 litres of H2O. Treatment to purify that water — eliminating minerals that would gum up the works — consumes another 15 litres of water per kilogram of H21.That’s not the end of the story, however. There’s a lot more water use to be counted if the renewable energy that powers the process is included. The operation of solar panels and wind turbines might not consume much water, but manufacturing them does. All told, manufacturing a wind turbine adds 11 litres to green hydrogen’s water footprint. And the manufacture of today’s leading variety of solar power adds a huge 124 litres, mostly from the fabrication of silicon photovoltaic wafers.Still, the water requirements of hydrogen production seem to be manageable. As part of an analysis co-led by Rosa, one scenario for a net-zero global economy in 2050 that consumes 400 megatonnes of green hydrogen per year would use a meagre 0.13% of the world’s available water supply if the energy came entirely from wind power, and about 0.56% if it all came from solar power 2.Countries that already face water scarcity, Rosa and his colleagues argue, could choose to import hydrogen to meet domestic needs rather than ramping up production. In fact, many of the countries that their study identified as land-limited are already working to foster a hydrogen trade, including Japan and parts of Europe. Other regions and nations — including areas of sub-Saharan Africa, South America, Canada and Australia — have sufficient land and water to become major hydrogen exporters, and many are already gearing up to fulfil this role.Multiple factors suggest that the impacts of green hydrogen on regional water could be even more limited than Rosa’s findings suggest. For example, over the past few years analysts and energy planners have lowered their estimates of how much green hydrogen will be produced over the long term. In its September prediction for limiting global temperature rise to 1.5 °C, the International Energy Agency (IEA) projects there will be one-fifth less hydrogen use in 2050 than it had predicted in its 2021 report.Another important consideration when computing hydrogen’s hydrological footprint is the capacity of hydrogen to be a substitute for fossil fuels, which are themselves water-intensive sources of energy. Most studies so far do not account for the effect of such a substitution. Rosa and his colleagues, for example, assume a fivefold reduction in petroleum refining between 2020 and 2050, as the use of gasoline and diesel is phased down. But they do not work in a corresponding reduction in water use, which could further improve hydrogen’s hydrological footprint. And if green hydrogen replaces natural gas, the substantial water consumption by gas producers that use hydraulic fracturing will be reduced. For example, many jurisdictions in the United States and Europe are considering using green hydrogen to fuel gas-fired power plants to cover gaps in supply from solar and wind farms.Love that dirty waterIn many cases, hydrogen producers might be able to avoid adding strain to potable water supplies by tapping polluted or salty water, instead of potable water. Options include municipal waste water, waste water from oil and gas production and even seawater. Water treatment and desalination plants are expensive to build, but the investment is comparatively small relative to the overall cost of hydrogen production.

Jack Brouwer, director of the Clean Energy Institute at the University of California, Irvine, demonstrates the electrolysis stack in a system used to make renewable hydrogen.Credit: Steve Zylius/UCI

In 2022, an analysis 3 by a team at Yale University in New Haven, Connecticut, concluded that even to treat seawater — the toughest water source to prepare as input to such a facility — would require only 0.3% of an electrolysis plant’s total energy budget. “The bottom line is that “we do not need to consume freshwater resources used for drinking” to produce hydrogen, says Lea Winter, a chemical and environmental engineer at Yale and the study’s lead author. The International Renewable Energy Agency agrees, concluding in 2020 that: “Even in places with water stress, seawater desalination can be used with limited penalties on cost or efficiency.”In California, electrolyser manufacturer Plug Power in New York plans to build a water-treatment plant and hand it over to the local municipality, in return for a source of water for hydrogen production. Mendota, where the plant is to be built, is currently depleting ground water to meet demand for potable water. City officials say that the new plant will clean up sewage to increase the city’s water supply, so that it can reduce its use of ground water and sell water to Plug Power.Using seawater presents almost limitless potential, but also troubling environmental impacts. Some desalination plants release heated brines laden with treatment chemicals back into the sea; they can also suck in and destroy marine creatures. The most significant ecosystem impact of these plants, according to a 2020 review4, is lethal osmotic shock to marine organisms, including fish, plankton and algae when super-salty brines cause their cells to dehydrate. Most at risk are organisms in semi-closed seas such as the Red Sea, the Mediterranean and the Persian Gulf. Nearly half of the world’s desalination capacity is concentrated in the Persian Gulf.Some observers, however, foresee potential environmental dividends if hydrogen producers tap seawater and waste water. Thomas Adisorn, a political scientist at Germany’s Wuppertal Institute for Climate, Environment and Energy, sees potential for projects such as that of Plug Power to improve the environment by supporting international development. “Putting more effort into using recycled waste water in developing countries that are exporting hydrogen could raise their capacity to build wastewater infrastructure,” says Adisorn, who organized a meeting in 2022 to help officials from water-scarce Jordan who were planning its hydrogen economy.New technology and engineering integrations promise to trim the cost of non-conventional water use even further, while capturing other valuable benefits that pay for the extra water treatment. One active area of research and development, for example, would monetize green hydrogen’s oxygen by-product. Aerobic treatment tanks at wastewater plants rely on pumped air to sustain their waste-eating microbes. According to Brouwer, some large wastewater plants pump in pure oxygen instead of air to spur faster digestion. With an electrolyser they could get that oxygen for free, says Brouwer, rather than operating pricey air-separation units.Researchers with the municipal water authority Sydney Water and the University of Sydney, Australia, estimated in 2022 that integrating electrolysers into wastewater treatment plants could save the city about US$1.5 million per year 5. They calculate that the city’s 13.7 gigalitres per year of unused effluent could yield 0.88 megatonnes of green hydrogen per year — one-tenth of the amount Australia and New Zealand are expected to produce in 2030, according to analysts S&P Global in New York. Sydney Water says that its unpublished research confirms the viability of hydrogen and oxygen production using its treated water, following further purification.Another innovation that could prove a major benefit to using seawater for hydrogen production is the ability to operate electrolysers offshore. Over the past year, teams in China and Europe have deployed platforms combining desalination equipment and electrolysers. The hope is that the floating electrolysis plants — if they can operate reliably amid storms and other assaults to offshore hardware — will cut the cost of offshore wind energy. Shipping hydrogen through pipelines is generally cheaper than moving the equivalent amount of energy through electrical transmission lines, and hydrogen proponents are betting that this rule will hold for passing energy from offshore wind farms back to land.The hydrogen producer Lhyfe’s 1-megawatt pilot platform operated offshore for 5 months this year using desalinated seawater, and a 10-megawatt platform is planned for Belgian waters in 2026. Lhyfe in Nantes, France, wants to mitigate the impact of desalination by eschewing chemical additives in its treatment process, and by diluting brine with extra seawater, says Stéphane Le Berre, Lhyfe’s offshore project manager.Lhyfe is now exploring whether the oxygen from offshore electrolysis could counteract declining levels of dissolved oxygen in the ocean — conditions that are stunting marine ecosystems in some regions. In July, researchers projected that artificial oxygenation from global deployment of offshore wind farms and electrolysers could reduce the volume of severely hypoxic zones by 1.1–2.4%6. But they also reported some counterintuitive regional impacts. For example, their simulation projected that oxygen injection might enlarge an existing hypoxic zone in the Indian Ocean’s Bay of Bengal.Known unknownsTechnological wild cards, meanwhile, could alter water consumption calculations around hydrogen production. In a review, the IEA identified 40 companies that are exploring a potential hydrogen source that might be cleaner than electrolysis: natural pockets of the gas, some of which might be tapped using little water. But, as with injecting oxygen in to the sea, seemingly water-saving technologies could have perverse effects. Accessing ‘geological’ hydrogen might require fracturing of rock layers akin to hydraulic fracturing or ‘fracking’ used to recover oil and gas. And some of the hydrogen prospectors plan to stimulate hydrogen production in situ by injecting water into iron-rich rock formations.Green-energy company Eden GeoPower in Somerville, Massachusetts, plans to test hydrogen stimulation in the peridotite rock formations of water-scarce Oman, in collaboration with the country’s Ministry of Energy and Minerals. The company hopes to increase underground permeability using its water-free electrical fracturing technology. Chief executive Paris Smalls, says “back of the envelope calculations” suggest that net water consumption will be comparable with that of electrolysis per kilogram of hydrogen delivered.Eden GeoPower’s attention to water resources is the exception to the rule among hydrogen producers. Water supply is not mentioned in the IEA report or in a 2022 “critical” review of hydrogen-production technology 7.Given that hydrogen production and water use are inextricably bound, it is unlikely that water supply will continue to be omitted. The inconvenient truth, say both Brouwer and Rosa, is that solar energy is the cheapest source of low-carbon power available to produce hydrogen, but the regions with the best solar resources are also some of the most parched.Brouwer is one of the main team members behind California’s hydrogen-development programme, which picked up $1.2-billion of the $7 billion in US federal funds awarded in October to regional ‘hydrogen hubs’ that link producers and consumers. He says that hydrogen plants can tap into conventional water supplies or clean up waste water, but that reaching net-zero carbon emissions in California will ultimately require a lot more solar panels in the desert.Converting that solar energy to hydrogen will force the state to build more infrastructure, and to make an important choice. As Brouwer puts it: “We’re going to eventually have to figure out whether we want to run big wires from the solar resource to where the water is, or big pipes sending water to the desert.” More

Floods, droughts, pollution, water scarcity and conflict — humanity’s relationship with water is deteriorating, and it is threatening our health and well-being, as well as that of the environment that sustains us. The good news is that a transition from the water policies and technologies of past centuries to more effective and equitable ways of using and preserving this vital resource is not only possible, but under way. The challenge is to accelerate and broaden the transition.Water policies have typically fostered a reliance on centralized, often massive infrastructure, such as big dams for flood and drought protection, and aqueducts and pipelines to move water long distances. Governments have also created narrow institutions focused on water, to the detriment of the interconnected issues of food security, climate, energy and ecosystem health. The key assumption of these ‘hard path’ strategies is that society must find more and more supply to meet what was assumed to be never-ending increases in demand.That focus on supply has brought great benefits to many people, but it has also had unintended and increasingly negative consequences. Among these are the failure to provide safe water and sanitation to all; unsustainable overdraft of ground water to produce the food and fibre that the world’s 8 billion people need; inadequate regulation of water pollutants; massive ecological disruption of aquatic ecosystems; political and violent conflict over water resources; and now, accelerating climate disruption to water systems1.A shift away from the supply-oriented hard path is possible — and necessary. Central to this change will be a transition to a focus on demand, efficiency and reuse, and on protecting and restoring ecosystems harmed by centuries of abuse. Society must move away from thinking about how to take more water from already over-tapped rivers, lakes and aquifers, and instead find ways to do the things we want with less water. These include, water technologies to transform industries and allow people to grow more food; appliances to reduce the amount of water used to flush toilets, and wash clothes and dishes; finding and plugging leaks in water-distribution systems and homes; and collecting, treating and reusing waste water.Remarkably, and unbeknown to most people, the transition to a more efficient and sustainable future is already under way.Singapore and Israel, two highly water-stressed regions, use much less water per person than do other high-income countries, and they recycle, treat and reuse more than 80% of their waste water2. New technologies, including precision irrigation, real-time soil-moisture monitoring and highly localized weather-forecasting models, allow farmers to boost yields and crop quality while cutting water use. Damaging, costly and dangerous dams are being removed, helping to restore rivers and fisheries.

Source: US Geological Survey

In the United States, total water use is decreasing even though the population and the economy are expanding. Water withdrawals are much less today than they were 50 years ago (see ‘A dip in use’) — evidence that an efficiency revolution is under way. And the United States is indeed doing more with less, because during this time, there has been a marked increase in the economic productivity of water use, measured as units of gross domestic product per unit of water used (see ‘Doing more with less’). Similar trends are evident in many other countries.

Source: US Geological Survey/US Department of Commerce.

Overcoming barriersThe challenge is how to accelerate this transition and overcome barriers to more sustainable and equitable water systems. One important obstacle is the lack of adequate financing and investment in expanding, upgrading and maintaining water systems. Others are institutional resistance in the form of weak or misdirected regulations, antiquated water-rights laws, and inadequate training of water managers with outdated ideas and tools. Another is blind adherence by authorities to old-fashioned ideas or simple ignorance about both the risks of the hard path and the potential of alternatives.Funding for the modernization of water systems must be increased. In the United States, President Biden’s Infrastructure Investment and Jobs Act provides US$82.5 billion for water-related programmes, including removing toxic lead pipes and providing water services to long-neglected front-line communities. These communities include those dependent on unregulated rural water systems, farm-worker communities in California’s Central Valley, Indigenous populations and those in low-income urban centres with deteriorating infrastructure. That’s a good start. But more public- and private-investments are needed, especially to provide modern water and sanitation systems globally for those who still lack them, and to improve efficiency and reuse.Regulations have been helpful in setting standards to cut waste and improve water quality, but further standards — and stronger enforcement — are needed to protect against new pollutants. Providing information on how to cut food waste on farms and in food processing, and how to shift diets to less water-intensive food choices can help producers and consumers to reduce their water footprints3. Corporations must expand water stewardship efforts in their operations and supply chains. Water institutions must be reformed and integrated with those that deal with energy and climate challenges. And we must return water to the environment to restore ecological systems that, in turn, protect human health and well-being.In short, the status quo is not acceptable. Efforts must be made at all levels to accelerate the shift from simply supplying more water to meeting human and ecological water needs as carefully and efficiently as possible. No new technologies need to be invented for this to happen, and the economic costs of the transition are much less than the costs of failing to do so. Individuals, communities, corporations and governments all have a part to play. A sustainable water future is possible if we choose the right path. More

Old Delhi’s Red Fort, a nearly 400-year-old structure where India’s flag is hoisted every Independence Day, is separated from the Yamuna River by a 55-kilometre ring road that circles the capital. I drive past it on this road, built on an old floodplain, on my way to work at Ashoka University in the neighbouring state of Haryana, a further 30 kilometres or so upstream. The river is hidden from view in places but it can be seen farther along, narrow and darkened by pollution for most of the year.In July 2023, flood water from heavy monsoon rains entered the Yamuna from Haryana, flooding parts of Delhi. TV images of the river lapping at the walls of the Red Fort recalled nineteenth-century paintings of the old course of the river.
Nature Spotlight: India
The Yamuna forms from the melting glaciers of the lower Himalayas, running for more than 1,370 kilometres until it merges with the Ganga in the city of Prayagraj in Uttar Pradesh. Delhi lies along its banks for just 20 kilometres, less than 2% of the river’s total length. But in that short stretch, the city belches out around 80% of the pollution found in the Yamuna. In some seasons, a foamy mixture of sewage and industrial waste coats the river surface in parts of Delhi. Newspapers carry pictures of Hindu devotees offering morning prayers while standing knee-deep in this toxic foam.Much of Haryana’s ground water is used to cultivate rice. Farmers pump it up using electricity that the state government heavily subsidizes to encourage agriculture. Without economic incentives to use this electricity sustainably, groundwater levels declined precipitously from the 1990s into the early 2000s. To combat this, legislation was introduced in 2009 to restrict the sowing of rice to mid-June onwards, timed to begin after the start of the monsoon season. Previously, rice planting had started as early as May.This means that the rice-harvesting season ends even closer to the wheat planting season, which begins in November. Farmers need to get rid of their rice-crop residue as soon after harvesting as possible to clear space for the wheat.Burning the crop residue is the cheapest solution. But in the early winter months, smoke and dust released from a combination of residue burning and other sources is concentrated by frequent changes in temperature and stagnant winds, and shrouds northern India. Schools are closed, construction work is halted and flights are grounded because of the poor visibility. Hospitals fill with people complaining of breathing difficulties. Each resident of Delhi is thought to lose nearly 12 years of their life to air pollution.As the world’s climate changes, extreme events such as the rains that led to the Delhi floods in July will become more common. The southern Indian state of Kerala witnessed a devastating flood in 2018, the worst in almost a century of recorded history. More than one million people were evacuated to higher ground. A study that year showed that about 60% of the coast of Kerala was eroding, and areas where good fishing could be found were shifting, affecting the lives of one million fishers and their families.Two large Indian cities, Chennai, on the Bay of Bengal, and Kolkata, on the banks of the Hooghly River, are expected to be at significant risk from sea-level rise in the next few decades. Along with the resulting intrusion of salt water into groundwater systems, this will increase climate-change-induced migration. The Sundarbans, an ecologically sensitive wetland system on the Bay of Bengal that contains the largest mangrove forest in the world, has already seen substantial climate-change-driven migration into the nearby city of Kolkata.The Namami Gange Programme is one of many started since the mid-1980s to clean up India’s iconic holy river, the Ganga. Around US$3 billion for this has been set aside or spent since 2014, largely on new sewage-treatment plants.But pollution levels remain stubbornly high, the result of lax enforcement of control measures and unregulated river-front development. More data are needed, and more transparency on the causes, so citizens can hold civic bodies and elected representatives responsible.Science can help too. The Ministry of Earth Sciences is funding several initiatives aimed at improving India’s ability to model the monsoon. This will help provide actionable advance warnings of extreme rain events. More research on the geomorphology of coastal India, on near-shore ocean current patterns and on the impact of sea walls could aid the design of interventions to slow coastal erosion.Fresh water is a finite and vulnerable resource that should be managed in a participatory fashion. Citizen groups in the south-Indian city of Bengaluru are helping to renew urban water bodies, reconfiguring them as centres around which communities can coalesce. In arid areas, such as the deserts of Rajasthan and Gujarat, old methods of rainwater harvesting are being revived, helped by traditional community knowledge.Guaranteeing a minimum amount of fresh water for each individual, free of charge, will ensure broader societal equity. Beyond that limit, water usage should be priced, creating an economic incentive for its sustainable use. Such a policy was introduced nearly a decade ago by the Delhi government, but continued groundwater extraction using illegal borewells has partly neutralized this positive step.Ensuring the sustainable use of water intersects climate change, agriculture, politics, pollution, migration and much more. Well-intentioned policy measures, such as subsidizing electricity for agriculture, can have unexpected consequences for water and its sustainable use.Placing water at the centre of our thinking about sustainability can help avoid such pitfalls. We need more conversations about water. More

Groundwater pumped on to Dennis Hutson’s farm in Allensworth, California, had dangerously high levels of arsenic. New technology tested on the farm reduced the levels to drinking-water standard.Credit: Adam Lau/UC Berkeley

In 2022, Ashok Gadgil conducted the first field trial of a water-treatment system for the 600 or so residents of Allensworth, California, who have been battling arsenic contamination for some time. The system is a more efficient iteration of technology that Gadgil and his team installed in India in 2016 to provide rural and marginalized communities with access to safe drinking water at low cost1. Like many small rural communities, Allensworth — a historically Black town with a majority Latinx population today — has no access to high-quality surface-water treatment facilities that are common in urban areas. Instead, these communities often use wells, which are at high risk of contamination with arsenic and other toxic substances.It’s an urgent issue in California: roughly 300,000 of the state’s 39 million residents drink from wells in the state’s rural areas and are therefore exposed to high levels of arsenic in the ground water. “Safe drinking water, which is a big chunk of our work, is all related to rural areas,” says Gadgil, who worked as an environmental engineer for 35 years at the state’s Lawrence Berkeley National Laboratory, and in July assumed an emeritus role at the University of California (UC), Berkeley. His team plans to return to Allensworth next year to continue testing the system, which makes use of technology, developed by a team that included Gadgil’s colleague Siva Bandaru, that uses hydrogen peroxide to rapidly oxidize iron so that it binds to arsenic and removes it from water.California, like many US states, has a mounting number of rural concerns, including not just safe water supplies, but also wildfire preparedness, air quality and equitable access to health care. Researchers in the UC system have key roles in monitoring and addressing such concerns. In addition to the ten academic campuses spread across the state, the UC system has a network of Agriculture and Natural Resources extension centres that serve as bridges to rural areas. Roughly 270 researchers are employed by these centres to support all 58 state counties through collaboration with other UC teams, as well as working with other public and private organizations. And even though funds for these centres have been waning over the past two decades, they are currently allocated around US$100 million of the UC system’s US$47-billion budget for 2022–23 to rebuild their dwindling workforces.
Millions of jobs in food production are disappearing — a change in mindset would help to keep them
It’s a welcome boost for researchers who face unique challenges in rural settings, where the remoteness of the communities can be a barrier to participation and engagement and cultural differences and concerns about confidentiality can cause some residents to be wary of academics. The most successful collaborations between urban-based researchers and rural communities have been based on a commitment to building trust, bridging political divides and delivering meaningful results, say researchers with experience in these settings.A growing number of scientists are pursuing community-based research partnerships2. A common motivation, says Gadgil, is a sense of urgency in addressing environmental-justice issues, especially in historically excluded communities. Researchers at public universities, such as those in the UC system, often have a sense of responsibility to give back to the citizens that fund their mission, he says, adding that some of the most satisfying projects use innovative technologies to find solutions to these communities’ problems. “Scientists are always looking for new frontiers,” says Gadgil.The regional contribution of the UC system is also apparent from Nature Index data on science cities (see ‘Deep connections’ and ‘Slipping back’).Centring community voicesAnn Cheney, a medical anthropologist at UC Riverside, conducts health research in partnership with communities living near the Salton Sea, California’s largest saline lake, roughly 50 kilometres north of the Mexican border. Over the past few decades, the lake has been shrinking owing to drought and reduced run-off from agriculture, which has increasingly exposed the lake bed. This has become a growing source of dust in a region that already has higher than average rates of childhood asthma compared with the rest of the state3.In 2017, Cheney and her colleagues worked with researchers at the US Border Health Commission to identify the health needs of Mexican immigrants in rural southern California. Childhood health was at the top of the list. Since then, she has partnered with local groups to further analyse health impacts, particularly in undocumented immigrants. A major challenge, she says, is that many of these communities have grown resentful of urban academics who — backed by hefty grants — swoop in to collect their data but then fail to return with solutions. “My fear, and what I’ve already seen happen, is the continued exploitation of these incredibly vulnerable communities,” Cheney says.

The largest minority population in California’s rural areas is Latinx people. Cheney, who has become fluent in Spanish so that she can engage with community members more effectively, says that the small number of Latinx staff at academic institutions in California, relative to the general population, makes it difficult to involve local voices in research. It can be time-consuming to partner with community members in identifying research needs, incorporating local knowledge and implementing research findings, and it comes at a cost, says Cheney, given that academic career advancement is typically based on publications.William Porter, who works with Cheney at UC Riverside, says that the Salton Sea’s growing dust problem was too much for him to ignore. An atmospheric scientist, Porter had originally arrived at UC Riverside in 2017 to focus, in part, on wildfire and coastal air quality. But he soon felt an urgent pull. “It’s right here in my backyard,” he says.Over the past few years, Porter has tailored research programmes to track dust storms and their acute health effects. He’s also launched a project to help the region’s residents to build their own indoor air purifiers using box fans and air filters. Scientists are uniquely positioned to address the consequences of policy indecision when it comes to complex environmental crises, he says, and he sees the Salton Sea’s environmental decline as a pressing opportunity to build research capacity around climate-related problems that are becoming increasingly common worldwide. What’s clear, says Porter, is that the days of the ‘ivory tower’ model of research dissemination are over; academics can no longer just publish a paper and assume the results will be delivered to communities. “That is a broken model,” he says. “The way you conduct community research nowadays is as part of a team with communities.”As California’s rural areas experience wildfires, flash floods, heatwaves and drought, researchers are asking what they can do to help, says Diana Moanga, who manages the Spatial Analysis Center at Stanford University in California. Throughout her career in California, Moanga has interviewed ranchers affected by dwindling water supplies, helped to create a risk index of mobile homes that are vulnerable to wildfires and assessed the potential for solar projects on tribal lands. Notably, she says, funders want to ensure that research results reach communities. Federal agencies such as the National Oceanic and Atmospheric Administration and the US National Science Foundation will not fund projects that do not set out clear community impacts — as well as a clear plan to disseminate the results back to community members.
Water crisis: how local technologies can help solve a global problem
Gadgil agrees that rural-community projects must avoid top-down approaches to be successful. In fact, his team always asks community members how else they would like to use scientists’ skills. Most often, the researchers provide teaching modules on making drinking water safe. They have even helped rural students with their science-fair projects. In his experience, if locals aren’t engaged, “as soon as you leave, the intervention will die”. It’s important to set appropriate expectations when embarking on a project, he says, by explaining how the science works, and emphasizing that a few failures might occur before the problem is solved.Better yet, says Susana Matias, a researcher who sits at the nexus between UC Berkeley, the Agriculture and Natural Resources network and community members, is sharing the leadership and decision-making. When analysing data from the state’s largest farmworker population health surveys4, for instance, Matias found increased risk of chronic health conditions, notably obesity, compared with elsewhere in the country.For example, in one project, Matias and her team partnered with a berry grower, who allowed them to run a health-promotion programme focusing on diet and exercise with farmworkers in their fields in California5. Although the programme did not measurably improve health outcomes, the researchers think it was highly valuable in engaging the farmworker community. “Roughly half of these populations are potentially undocumented immigrants, so it is key to have community-based partners to help build trust and access,” says Matias, who emphasizes that placing value on community members’ time and expertise is an important way to build mutual respect and workforce capacity.The value of rural dataInvolvement by rural residents is particularly important in medical research. People living in rural areas are more likely to die from heart disease, cancer, chronic respiratory disease and stroke than are urban dwellers, according to the US Centers for Disease Control and Prevention, but securing their participation in trials and surveys can be major challenge. Participants typically have to contribute their time during business hours, which might not be feasible for those in full-time employment, especially when they live far from urban centres. “Rural participants are often excluded from clinical research,” says epidemiologist Jennifer Radin.

By encouraging participants to engage with studies remotely, Radin and her colleagues at Scripps Research in La Jolla, California, and Johns Hopkins University School of Medicine in Baltimore, have been able to gather high-quality rural-health data. From 2017 to 2019, for example, they ran POWERMOM, a nationwide pregnancy health study in which participants could share data on blood pressure, weight-gain and other factors throughout their pregnancies, through a smartphone app6. Of the 3,612 participants who were initially recruited, 16% had rural addresses — a high percentage compared with previous studies, says Radin. “Doing a completely remote clinical trial allowed us to include everyone,” she says.In 2020, Radin launched another study, called DETECT, which used wearable devices to predict outbreaks of COVID-19 in the United States. The team also conducted outreach in far-flung locations, such as rural Alaska and Guam, to ensure that diverse populations were represented. The initial results, published last year, showed that symptom and sensor data collected by smartwatches and activity trackers could improve surveillance of COVID-197. “These digital tools can be rolled out anywhere, at any time — not necessarily only when it’s convenient for the researchers, but when it’s convenient for the participant to share their data and experience,” says Radin.Perhaps the greatest health impact, however, comes from the UC Programs in Medical Education (PRIME), which aim to address California’s looming physician shortage, especially in rural areas, where only 9% of the state’s doctors practise. The programme has resulted in more than 750 medical-school graduates since 2004, and roughly 43% of those graduated from programmes based in or serving rural areas.It’s projects such as this, which centre societal needs and priorities, that Gadgil hopes will attract greater funding and resources in future, alongside curiosity-driven science. “Research that benefits the communities around us is receiving much more focused attention,” he says. More

A sample of lanthanum (iii) nitrate under the microscope.Credit: Christian Wei/Zoonar/Alamy

The fermented drink kombucha seems about as far away as possible from the mining of heavy metals. But Alexa Schmitz, chief executive at the biomining company REEgen in Ithaca, New York, sees parallels between her firm’s bacteria-based product and the tangy beverage.REEgen’s bacterial ‘soup’ dissolves ground-up rocks, waste electronic components and other solids that contain rare-earth elements — metals that have valuable conductive, magnetic and fluorescent properties and that are used in everything from mobile phones to wind turbines. The metals impart strength and hardness to alloys, for example, and are found in superconductors and catalytic converters. But Schmitz notes that the company’s product is much less hazardous, both to people and to the environment, than are the chemicals typically used to separate metals from ore. “We’re producing a solution that is proving to be about as good as concentrated nitric acid at dissolving solids,” says Schmitz. “But it’s a little bit like kombucha. You can stick your hand in a vat of it and come out unscathed.”Rare-earth elements include those in the lanthanide series — those with atomic numbers from 58 to 71, usually shown as a pop-out beneath the main periodic table — as well as the group 3 transition metals scandium and yttrium. They are used in products such as magnets, light bulbs and electric cars, and end up in various waste streams, including mining tailings and ash from coal plants.Despite their name, rare- earth elements (REEs) aren’t all that uncommon, but they don’t tend to be found in concentrated deposits (unlike, say, a vein of gold). Miners might have to excavate one tonne of rock just to obtain a gram of REEs, says Buz Barstow, a synthetic biologist and Schmitz’s former adviser at Cornell University in Ithaca.
How a protein differentiates between rare-earth elements
They’re also difficult to purify. REEs tend to co-occur in natural deposits and are chemically similar. The conventional purification process involves repeatedly separating the metals, in dozens or even hundreds of cycles, using aqueous acids and organic solvents such as kerosene. It’s inefficient, costly and damaging to health and the environment. Much of the globe’s REE separation currently takes place in China.Now, Schmitz and a small but growing cadre of researchers are investigating a possible alternative: biomining. Many microorganisms naturally concentrate metals, and some are already used to mine copper and gold. The discovery about a decade ago of microbes that use lanthanides for their metabolism1,2 allowed researchers to explore the feasibility of adapting the microorganisms or their components to isolate REEs. The US Defense Advanced Research Projects Agency (DARPA) in Arlington, Virginia, has invested around US$43 million in research–industry partnerships to develop biomining for REEs.There’s room for microbes at every step of the biomining process, says Dan Park, an environmental microbiologist and DARPA grant team member at Lawrence Livermore National Laboratory in Livermore, California. For starters, many microbes secrete acids that can solubilize metals from rocks, discarded appliances and other electronic waste. Some make proteins that specifically interact with REEs, giving scientists the opportunity to isolate the elements from other metals, and perhaps even from each other.But scaling up microbe-based mining and remediation from the bench to an industrial process, in a way that would be practical and economical, involves substantial challenges.Each DARPA project on REEs, for example, has a goal that is puny by industrial standards: by 2026, the teams must to be able to purify 700 grams of material in a week. “It is really a baby step,” says Linda Chrisey, a programme manager for biological technologies at DARPA. “The most important thing is, can we do it?”Microbe minersWhatever the starting material, the first step in biomining is to grind it up and isolate the metals from everything else. Acid is often used to solubilize metals, and the acids produced by microbes are environmentally friendly, economical options. Researchers at Idaho National Laboratory in Idaho Falls, for instance, zeroed in on Gluconobacter oxydans, an acid-producing bacterium found in garden soil, fruits and flowers, as a potential microbe miner. The organism has no designs on the REEs themselves, says Barstow, who also works with G. oxydans. Rather, the acid it produces dissolves phosphates that it then uses in DNA; the liberation of REEs is a collateral benefit that humans can exploit.In experiments at Idaho National Laboratory, G. oxydans secreted a gluconic acid mixture that was better at leaching rare metals from industrial waste than was a comparable concentration of commercial, pure gluconic acid3. “We think there are other things being produced besides the gluconic acid,” says Vicki Thompson, a chemical engineer at the lab.Gluconobacter oxydans has a long history in biotechnology applications and a sequenced genome that is accessible to genetic tools. Schmitz, Barstow and their colleagues tapped these tools to optimize leaching of REEs by G. oxydans. The researchers began with a gene knockout screen, disrupting 2,733 of the microbe’s non-essential genes to identify more than 100 that influence gluconic acid output4.Disruption of G. oxydans genes involved in the uptake of phosphate resulted in the microbes producing a solution that was more acidic and more effective at leaching REEs5. “We convince them they’re starving for phosphate,” explains Schmitz. Work at REEgen to combine genetically engineered G. oxydans with optimization of the firm’s processes has boosted leaching by up to five times compared with wild-type microbes, Schmitz says.Separation anxietyAfter leaching, the next step is to isolate REEs from other metals that come out in acid, such as calcium and iron. Here, some surprising biology comes to the rescue. REEs were once thought to have no direct relevance to living organisms. Then, in 2012 and 2013, researchers reported that REEs are used by certain microbes to metabolize methanol1, and are even vital to the survival of microorganisms living in volcanic mud pots in Italy2.Lanthanides, it turned out, provide essential cofactors for microbial enzymes called alcohol dehydrogenases, some of which convert methanol to formaldehyde as part of metabolism. In fact, use of lanthanides as enzyme cofactors is widespread among microbes, even those that don’t eat methanol, says Cecilia Martinez-Gomez, a microbial physiologist at the University of California, Berkeley. Researchers are now adapting these microbes, or just their REE-binding molecules, to concentrate the desired elements.

A worker walks past a stack of waste computers at a recycling yard in Accra, Ghana.Credit: Christian Thompson/Anadolu Agency/Getty

Martinez-Gomez’s group, for instance, works with another lanthanide-using organism called Methylobacterium extorquens, which is found in a variety of locations, such as plants and the oceans. She and her team identified a set of ten M. extorquens genes6 that produces a small metal-binding molecule that the team named methylolanthanin. The microbes secrete methylolanthanin into their surroundings, where it sticks to nearby lanthanides, which are otherwise insoluble. The complex is then taken up by a microbial transporter and brought into the cell to serve as a cofactor for alcohol dehydrogenase.M. extorquens also has a system to store lanthanides for later use, saving the metals either in granules or in structures that the researchers called lanthasomes7. This, presumably, allows the bacterium to prepare for a lanthanide drought; it can stockpile enough of the metals to last for several microbial generations, says Martinez-Gomez.To improve lanthanide uptake for biomining purposes, she and her team engineered a strain of M. extorquens that allowed them to control and scale up methylolanthanin production. This more than tripled the microbes’ ability to collect neodymium and other REEs from pulverized magnets, Martinez-Gomez says. Then it’s a relatively simple matter of breaking open the cell and precipitating the lanthanides. The process results in REEs that are more than 98.8% pure, says Martinez-Gomez, who co-founded a company, RareTerra in Berkeley, to commercialize accumulation and separation of lanthanides by M. extorquens.The bacterium has also yielded a tool that has become key to the burgeoning field of rare-earth biomining. Discovered in 2018, lanmodulin is a lanthanide-binding molecule8 that sits between the two outer membranes of the bacterium, alongside the alcohol dehydrogenases that use lanthanides as a cofactor. Co-discoverer Joseph Cotruvo Jr, a biochemist at Pennsylvania State University in University Park, still isn’t sure what lanmodulin does there. “We kind of got sidetracked by the interesting properties and technological applications,” he says. For example, his group, Martinez-Gomez and others are adapting parts of the protein to create luminescent and fluorescent biosensors. These could highlight where REEs are present or accumulating9,10, and might even be used to remediate REE contamination of water sources11.Lanmodulin has provided researchers with a mechanism for isolating REEs, at least at the benchtop scale. Park, a collaborator of Cotruvo’s, immobilized lanmodulin on agarose microbeads to create a column that could capture lanthanides. Starting with coal-mine ash from the northwestern United States, which contained less than 1% lanthanides overall, the team obtained a solution of 88.2% pure lanthanide12. “It was so selective that we could take really dilute, poor sources of rare earths, and selectively capture using lanmodulin,” says Park.Getting specificLanmodulin and M. extorquens are part of a small group of emerging tools for purifying REEs. Researchers have also designed lanthanide-binding peptide tags that can be encoded in a gene of interest. Originally intended to enhance X-ray crystallography and protein assays13, these are also finding applications in biomining.Researchers are studying the REE-collecting abilities of the model microbe Pseudomonas putida14 and of Methylacidiphilum fumariolicum — the species discovered in volcanic Italian mud pots15. And scientists in Germany have discovered that photosynthetic single-celled organisms called cyanobacteria can suck up REEs16 — although, as with G. oxydans, this doesn’t seem to be essential for their survival. The cyanobacteria can even absorb heavy metals into their cell walls if they’re dead, meaning that it might not be necessary to keep them alive to use them in metal purification, says biotechnologist Thomas Brück at the Technical University of Munich in Germany.
Metal-oxide cages open up strategy for processing nuclear waste
Whatever their source, once REEs are obtained, the most challenging step is to separate them from each other. There are 17 rare-earth metals, which are not necessarily interchangeable for commercial applications. Yet the smallest and largest lanthanide atoms differ in size by less than half an ångström. Their similarities in size and chemistry explain why the current chemical separation process is so laborious. Isolating individual REEs is “the problem that industry wants to solve the most”, says Cotruvo.Here, again, lanmodulin offers possibilities. Cotruvo and his colleagues scanned genome sequences for the most unusual lanmodulins they could find, homing in on a protein from a bacterium called Hansschlegelia quercus. It’s found on oak buds, where it can live on methanol released by the plant. Lanmodulin from H. quercus showed a preference for light lanthanides — those with atomic numbers of 62 or less — rather than for heavy ones with atomic numbers of 63 and up.Cotruvo’s group discovered that H. quercus lanmodulin distinguishes between the metals through a selective process. When the molecule encounters a light lanthanide such as neodymium or lanthanum, two lanmodulin monomers stick together to form a dimer, and do so more than 100 times more tightly than they do in the presence of a heavier lanthanide such as dysprosium. The lanmodulin protein probably doesn’t dimerize on Park’s columns, Cotruvo says, but nonetheless, that preference meant that a column of H. quercus lanmodulin could separate a mixture of neodymium and dysprosium into fractions that were more than 98% pure for each element17.“That’s really a significant breakthrough,” says Daniel Nocera, an inorganic chemist at Harvard University in Cambridge, Massachusetts. “It’s going down the road to selectivity.”And there are likely to be other tools out there, notes Martinez-Gomez, because microbes seem to have a wide variety of mechanisms for collecting, transporting and using lanthanides. “There are really interesting differences, so this is really a broad and emergent area of study,” she says.
NatureTech
To apply these tools to mining and recycling, researchers envision a series of steps. First, they’ll remove metals from the ore or waste material, then they’ll extract lanthanides from the other metals. At that point, they might enlist H. quercus lanmodulin or other tools to separate groups of lanthanides from each other, such as lights from heavies, until they have pure elements.But biology doesn’t have to solve all the separation problems, says Park, because the chemical process remains an option. If microbiologists could go from a low-grade leachate to a solution that is, say, 80–90% REE, they could pass it on to the chemists to finish the job. Even with partial biomining, the whole process might still use less energy and produce less toxic waste than an entirely chemical purification.Emphasis on ‘might’: the commercial viability of this biomining approach remains to be seen. “The system needs to be incredibly robust, otherwise it won’t be economically feasible,” says Marina Kalyuzhnaya, a microbiologist on a DARPA REE project at San Diego State University in California.The Idaho team has calculated how much it would cost to use G. oxydans to recover REEs from hazardous waste originating in petroleum production, and estimated that the process could be economical18. The biggest costs in terms of both money and environmental hazards were electricity to power the plant and glucose to feed the microbes, with the sugar alone accounting for 44% of the investment. But microbe miners don’t necessarily need pure glucose. Alternatives include maize (corn) stover — the stalks, leaves and cobs left over after harvests — or the starchy water that runs off potatoes after they’re washed. Switching to either of these inputs, the team calculated, cut costs by 17% or more19.Another key question is how long purification columns will last before they have to be replaced. So far in the lab, scientists have run their columns only dozens of times at most, but mining companies could require tens of thousands of runs. “Any time we talk to somebody in industry, that’s the first question they’ll ask,” says Park. “It’s still a pretty open question.”Park advises scientists interested in studying this kind of process to talk to people in the mining industry to understand their needs. He’s also found “a wealth of expertise” in advice from peers at the Critical Materials Innovation Hub, a collaboration between labs in academia, industry and the US Department of Energy, led by Ames National Laboratory in Iowa. Its goal is to accelerate work on rare-earth and other materials that are key to clean energy. Conferences and journals from the American Chemical Society are also great resources for those interested in REE purification, Park says.And should lanthanide biomining prove successful, it could be only the beginning. There are other elements found in relatively low-grade ores that manufacturers would love to concentrate, Barstow says. “Rare earths are just a test bed for all the other minerals,” he says. “We want to make microbes that are tailored for all the other metals.” More