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“In this photo, I’m visiting a once-abandoned well, known as the Three Trees Well, north of Bengaluru, India. In the past, this type of well would have been filled with concrete and the land used to build properties, but thanks to community outreach efforts it has been protected and cleaned by local community members. Their work has been rewarded by the well reconnecting with the below-ground aquifer and bringing water to the community again. It now contains around 3 metres of water during the peak summer months.This is a success story, and we need more of those. People on the city’s outskirts are struggling, and the state’s government has responded by arranging tankers to bring water from the Kaveri River, 100 kilometres away. Unfortunately, this kind of event is taking place across much of urban India. Around 50% of the supply in Indian cities comes from groundwater and, without it, life grinds to a halt.I work as an adviser for the Biome Environmental Trust in Bengaluru and develop policies related to sustainable water management. I am also an adjunct faculty member at Azim Premji University in Sarjapura, where I teach courses on water conservation and management.Here in Bengaluru, I’ve been working with the traditional well-digging community, known as the Mannu Vaddar or Bhovi, to complete works in the city and surrounding rural areas. If the culture of the well can be revived in India, it might help people to find a path to sustainability in the face of climate change.Since our success at the Three Trees Well, the government has funded a further programme to rejuvenate wells and shallow aquifers in 10 cities across India. Now, the government wants to replicate that programme across a further 5,100 urban areas in the country. I am a small part of this journey, and it all began with Bengaluru’s wells.” More

Almond farmers in California are under pressure to reduce the amount of water they use.Credit: Ed Young /Design Pics Editorial/Universal Images Group/Getty

From the Dust Bowl era of the 1930s in North America to the droughts in Ethiopia in the 1980s, Australia in the early 2000s and Syria, Iraq and Iran in 2020, the spectre of water shortages has long hung over the world’s farmlands. When rain fails to arrive season after season, crops wither and cattle starve, and famine and conflict often follow. Climate change brings a whole new level of unpredictability to the rainfall that farmers rely on, either to water their crops directly, or to feed the rivers, lakes, ground water and snowpack from which they draw water for irrigation. And that means agriculture is having to adapt — quickly.But crops that have been cultivated in the same place or cattle that have occupied the same rangelands for centuries can’t just be packed up and moved to a new area when rain patterns change. Instead, producers — and the governments that rely on them to nourish the populace and the economy — are having to rethink what is really involved in future-proofing an industry that humanity can’t live without. Some of the solutions lie in engineering crops to be more drought tolerant, or choosing crop varieties that are inherently better able to survive in drier conditions. But they also lie in an approach that requires economic and agricultural flexibility.
Nature Spotlight: Agricultural sciences
The Intergovernmental Panel on Climate Change has forecast that the percentage of the world’s population exposed to extreme drought will increase from 3% to 8% by 2100. If global warming exceeds 3 °C above pre-industrial levels, around 170 million people — mostly in low- and middle-income countries — face extreme drought.“I can see that Africa, Latin America and the Mediterranean continues to become drier,” says Hideki Kanamaru, a natural-resources researcher at the United Nations Food and Agriculture Organization in Rome. “These are particular areas of concern [because they] overlap with the historical trend of droughts.”Modelling suggests that rainfall will generally increase at higher latitudes — towards the poles — but decrease over subtropical areas. Over the past century, there has been a trend towards more rainfall in eastern North and South America, northern Europe, and northern and central Asia. However, there has been less rainfall overall in the Sahel, southern Africa, the Mediterranean and southern Asia. Climate change is also likely to alter monsoon rain patterns, which many agricultural regions rely on for predictable rainfall.However, this isn’t the only water-scarcity threat faced by producers. Amal Talbi, a hydrogeologist and water-resources management specialist at the World Bank in Washington DC, says that drought can also arise from economic water scarcity.Whereas physical water scarcity is when there is not enough water to meet the needs of agriculture or other uses that need fresh water, economic water scarcity is when, “you have the water, but you don’t have access to the water because you don’t have the infrastructure,” Talbi says. This distinction is important because the approach to solving these problems is very different.Flexible food strategiesPhysical water scarcity can be tackled in several ways. The first is to use less water overall: “Either you reduce your irrigation area, or you change the crops, so you use crops that use less water,” Talbi says. The second is to boost water sources with methods such as wastewater reuse or desalination plants.Another method is to be flexible with what crops are grown and when, and then use this to make the most of both water and market demand. This is the approach taken by Jordan, one of the most water-scarce nations. Receiving less than 50 millilitres of rainfall per year, the country is facing an even drier future, with its freshwater supplies per person now just 3% of what they were two decades ago, owing in part to climate change. Despite this, agriculture contributes around 30% of the country’s gross domestic product.

Severe droughts in eastern Australia in 2019 meant farmers had to feed cattle with fodder imported from the other side of the country.Credit: David Gray/Getty

Jordan’s answer to worsening water shortages is to focus on growing high-value, water-intensive crops for export, such as strawberries and tomatoes, in the central and northern Jordan Valley region. Although this area gets some rainfall, farmers also have access to the Jordan River and the King Abdullah Canal, an irrigation project that provides water to the Jordan Valley.It might seem illogical to grow water-hungry crops in a water-deprived landscape, but Talbi says it makes more sense than growing a crop such as wheat. “For the same land, what you would get in terms of these foods — exporting them, getting that money and then buying wheat — you will have much more than if you were using wheat in that area,” she says. Jordan also has another advantage: its climate means that those high-value seasonal products ripen earlier than they do in regions such as Spain and Portugal, so Jordan gets them to European markets ahead of other producers. “In a way, it is among the best countries in the region in terms of managing the water scarcity, given that they have so little options,” Talbi says.Morocco has a more complex water scenario to negotiate because different parts of the country experience different rainfall. Its largest crop is wheat, followed by barley, but it also produces high-value, water-hungry crops such as tomatoes, potatoes, citrus fruits and watermelon. Farmers and businesses there, like those in Jordan, grow high-value crops in irrigated areas where the water supply can be more carefully controlled and is therefore reliable, and save the less water-hungry crops for the rain-fed regions. “Roughly 50% of the time Morocco has a low rainfall, 50% it has good rainfall, so it has high variability,” Talbi says. When rainfall is good, they plant wheat and grains, and when it isn’t they maximize their irrigated high-value crops and use this money to buy wheat and to compensate the grain farmers.Change in the timesAnother factor that influences physical water availability is changes to the timing of previously predictable climatic patterns. In the northwest United States — Oregon, Washington and Idaho — wheat, tree fruit such as apples and cherries, and potatoes are the dominant crops. These are watered by a combination of rain and irrigation, the latter of which relies on the annual snowpack melting and delivering a flush of water to rivers and lakes in the Columbia River basin.But rainfall patterns are changing, says Georgine Yorgey, the associate director of the Center for Sustaining Agriculture and Natural Resources at Washington State University in Mount Vernon. “We’re going to hold less water in snowpack, more precipitation falling as rain at shoulder times of year and in shoulder elevations, and then also earlier snowmelt,” Yorgey says. And that has implications for planting and harvesting. “We have more of a mismatch between when the water comes and when the water is needed.”The timing of a crop’s sensitivity to water stress — when it is likely to have the greatest impact — varies between crops, Kanamaru says. “The last stage — ripening through harvest stage — they are not so sensitive to water stress,” he says. “The next critical stage is planting to early vegetation and the most critical stage is during reproduction.” If rainfall patterns change, it could mean that the timing of planting and harvesting of crops has to change. It’s not a new strategy in agriculture, but one that is being considered much more broadly in the face of shifting temperatures and rainfall patterns. One study has found evidence that the sowing of spring crops such as maize (corn), rice, sorghum and soya bean can shift by 10–30 days across different regions (S. Minoli et al. Nature Commun. 13, 7079; 2022). Another project in Australia found that moving the planting window for sorghum forward by four weeks reduced the risk of high summer temperatures causing heat stress during flowering (see go.nature.com/3vp3dt3).However, being flexible and tailoring each year’s agricultural focus to rainfall works only with crops that are planted and harvested in yearly cycles. It’s less viable for longer-lived crops, such as tree nuts, as California’s almond industry is discovering. The almond sector has quadrupled in size in the past 20 years, and is now the fourth largest agricultural commodity in the state, supplying around 80% of the world’s almonds. This expansion comes at a water cost: in 2021, the crop consumed 520 billion gallons more water than it did in 2017.

Strawberry farmers in Morocco grow the crop in irrigated areas where the water supply is carefully controlled but reliable.Credit: Youssef Boudlal/Reuters

In the past two years, drought has forced a reckoning, and there are now calls for the almond industry to reduce in size to preserve the state’s water supply in times of shortage. An almond tree can take around seven years to become fully productive, so it’s an industry that can’t just turn on a dime. As a result, producers are facing some tough decisions about its future viability in a drier, hotter climate.Cattle are a lot more mobile than an almond tree, but even in a country with grazing lands as vast and expansive as Australia’s, droughts have had devastating effects on this agricultural sector. “There were genuine shortages of feed for livestock. We had farmers in the eastern side of Australia with very hungry livestock, having to pay very high prices to ship grain and fodder from the other side of the country because there was none in eastern Australia,” says Neal Hughes in Geelong, Australia, who is an economist at the Australian Bureau of Agricultural and Resource Economics and Sciences — a national government research agency.Australia is usually a significant exporter of grain around the world, accounting for around 13% of all global wheat exports. But during the last devastating drought, which culminated in the Black Summer bush fires of 2019 and 2020, Australia’s contribution to wheat exports dropped drastically, and the nation even ended up having to import small amounts of grain to meet domestic needs, Hughes says. It was a shot across the bow of a country with an economy that is heavily dependent on its natural resources, warning that climate change could threaten a long-cherished status quo.An issue of accessEconomic water insecurity is a very different challenge, because solutions require a cross-disciplinary approach. A big issue is that the water exists, but requires efficient and affordable irrigation to enable farmers to get to it. In regions such as West Africa and the Sahel, the cost of irrigation is astronomical compared with that in other nations, Talbi says. For example, to irrigate one hectare in the Sahel can cost up to US$20,000, whereas doing the same in China might be around $600–700 per hectare, she says.One reason is that the supply chain for irrigation equipment is not yet established in Africa, so these products must be imported. Getting irrigation set up not only where it’s needed, but how it’s needed is also a challenge. Pumps and infrastructure can’t simply be parachuted in for free, Talbi says. Those systems have to be built from the ground-up if they are to be sustainable in the long term.Water isn’t the only challenge that agriculture faces in a climate-changed future, but historically it has been the most devastating, accounting for at least half of agricultural losses, Kanamaru says. And that’s only going to get worse. “Climate change is an additional amplifier to the long-standing problems of managing water,” he says.Finding solutions will require a holistic approach. “There are many parameters: variables we can modulate in this complex balance between demand and supply of water,” he says. “But I think we need to take a step back and look at the water budget of the whole hydrological cycle.” More

More than two billion people worldwide lack access to reliable, safe drinking water. Challenges around managing water resources are complex and wide-ranging. They are interlinked with those affecting land and food systems and are exacerbated by the climate crisis. Four scholars propose ways to prompt progress in water governance — and highlight just how crucial it is for local communities to be involved.

Farhana Sultana approaches research on environmental harms and social inequities in tandem.Credit: Wainwright Photos

FARHANA SULTANA: Collaborate to advance water justice Throughout my childhood in Dhaka, Bangladesh, the frantic call ‘Pani chole jaitese!’ (‘The water is running out!’) prompted my family, along with the entire neighbourhood, to scramble to fill pots and buckets with water before the taps ran dry. I witnessed women and girls walk long distances to secure this basic necessity for their families, long before water governance became central to my academic career. Amid water insecurity, the opposite extreme was just as familiar — going to school through devastating floods and experiencing the fall-out from disastrous cyclones and storm surges.Municipal water services in Dhaka also struggled to meet the growing demands of a rapidly urbanizing and unequal megacity. Access to electricity — needed to run water pumps — was sporadic, and there weren’t enough treatment plants to ensure clean water for millions of residents.These early experiences fuelled my dedication to tackling water injustices. Today, as an interdisciplinary human geographer with expertise in Earth sciences, and with policy experience gained at the United Nations, I approach environmental harms and social inequities in tandem — the root causes that connect both must be addressed for a just and sustainable future. My research also encompasses climate justice, which is inextricably linked with water justice. Climate change intensifies water-security concerns by worsening the unpredictability and severity of hazards, from floods and droughts to sea-level rise and water pollution.Such events hit marginalized communities the hardest, yet these groups are often excluded from planning and policymaking processes. This is true at the international level — in which a legacy of colonialism shapes geopolitics and limits the influence of many countries in the global south on water and climate issues — and at the national level.However, collaborative work between affected communities, activists, scholars, journalists and policymakers can change this, as demonstrated by the international loss-and-damage fund set up last year to help vulnerable countries respond to the most serious effects of climate-related disasters. The product of decades of globally concerted efforts, this fund prioritizes compensation for low-income countries, which contribute the least to climate change but often bear the brunt of the disasters.I also witnessed the value of collaboration and partnership in my research in Dhaka. Community-based groups, non-profit organizations and activists worked with the Dhaka Water Supply and Sewerage Authority to bring supplies of drinking water at subsidized prices to marginalized neighbourhoods, such as Korail, where public infrastructure was missing.Globally, safe water access for all can be achieved only by involving Indigenous and local communities in water governance and climate planning. People are not voiceless, they simply remain unheard. The way forward is through listening.

Tara McAllister is exploring the interface between Mātauranga Māori (Māori Knowledge) and non-Indigenous science.Credit: Royal Society of New Zealand

TARA MCALLISTER: Let Māori people manage New Zealand’s water I have always been fascinated by wai (water) and all the creatures that live in it. Similar to many Indigenous peoples around the world, Māori people have a close relationship with nature. Our connection is governed by geneaology and a concept more akin to stewardship rights than to ownership. This enables us to interact with our environment in a sustainable manner, maintaining or improving its state for future generations.I was privileged to go to university, where I studied marine biology. I then moved to the tribal lands of Ngāi Tahu on Te Waipounamu, the South Island of New Zealand, which triggered my passion for freshwater ecosystems. Intensive agriculture is placing undue pressure on the whenua (land) and rivers there. Urgent work was required. Undertaking a PhD in freshwater ecology, I studied the causes of toxic benthic algal blooms in rivers. For me, there is no better way to work than spending my days outside, with my feet in the water.

A worker fills people’s water containers from a tanker in Kolkata, India.Credit: Rupak De Chowdhuri/Reuters

Having just started a research position at Te Wānanga o Aotearoa, a Māori-led tertiary educational institution, I am now exploring the interface between Mātauranga Māori (Māori Knowledge) and non-Indigenous science, and how these two systems can be used alongside each other in water research. I have also been working on nurturing relationships with mana whenua, the community that has genealogical links to the area where I live, so that I can eventually work in the community’s rivers and help to answer scientific questions that its members are interested in.Despite a perception that Aotearoa (New Zealand) is ‘clean and green’, many of its freshwater ecosystems are in a dire state. Only about 10% of wetlands remain, and only about half of rivers are suitable for swimming. Water resource management is challenging, because of a change this year to a more right-wing government. The current government seems intent on revoking the National Policy Statement for Freshwater Management, established in 2020.This policy has been crucial in improving the country’s management of freshwater resources. Although not perfect, it does include Te Mana o te Wai — a concept that posits that the health and well-being of water bodies and ecosystems must be the first priority in such management. It is now in danger of being repealed.I think that, ultimately, our government’s inability to divulge control and power to Māori people to manage our own whenua and wai is what limits water resource management. More than any change in policy, I would like to see our stolen lands and waters returned.

Suparana Katyaini calls for more policy support for Indigenous-led water management.Credit: Milan George Jacob

SUPARANA KATYAINI: Consider water, food and land together Growing up in New Delhi, I always had easy access to drinking water — until the summer of 2004, when a weak monsoon triggered a water crisis and the city had to rely on water tankers. I realized then that good management of water resources supports our daily lives in ways we take for granted until we experience scarcity.My professional journey in research and teaching has been motivated by this experience. During my environmental studies of water poverty in India, I noticed that the field relied largely on quantitative data over qualitative insights — the degree of water-resources availability, access and use are typically assessed through metrics such as the water-availability index or the water-demand index. But in many places, Indigenous and local communities, including farmers and women in any occupation, have collectively developed skills to weather periods of water scarcity. Paying attention to these skills would lead to better water management. For example, the issue of food and nutritional insecurity in water-scarce areas in the state of Odisha, India, is being solved by Bonda people through revival of the crop millet, using varieties that are nutritious, water-efficient and climate-resilient.But these efforts need more policy support. My current work at the Council on Energy, Environment and Water explores how water, food and land systems are interlinked in India, and how better understanding of these relationships can inform policies. I am looking to identify similarities and differences in objectives of national and regional policies in each sector, as well as exploring whom they affect and their intended impacts. The aim is to move towards unifying water, food and land governance.

Michael Blackstock examines climate change from a water-centred perspective.Credit: Mike Bednar

MICHAEL BLACKSTOCK: Shift attitudes towards water In 2000, I conducted an ethnographic interview with Indigenous Elder Millie Michell from the Siska Nation in British Columbia, Canada, that transformed my interest in water from intellectual curiosity to passion. She passed a torch to me that fateful day. During our conversation for my research about the Indigenous spiritual and ecological perspective on water, she asked me: “Now that I shared my teachings and worries about water, what are you going to do about it?” She died of a stroke a few hours later.As an independent Indigenous scholar, I went on to examine climate change from a water-centred perspective — drying rivers, downpours, floods and melting ice caps are all water. This approach, for which I coined the term ‘blue ecology’, interweaves Indigenous and non-Indigenous ways of thinking. It acknowledges water’s essential role in generating, sustaining, receiving and, ultimately, unifying life on Mother Earth. This means changing our collective attitude towards water.In 2021, I co-founded the Blue Ecology Institute Foundation in Pavilion Lake, Canada, which teaches young people in particular to acknowledge the spiritual role of water in nature and in our lives, instead of taking it for granted as a commodity or ecosystem service. Giving back to nature with gratitude is also crucial. Such restrained consumption — taking only what is needed — would give abused ecosystems time to heal.A focus on keeping water healthy can help to guide societies towards more sustainable environmental policies and climate-change resilience — and ensure that future generations will survive with dignity. Critics say, ‘Blue ecology is kinda out there.’ In my view, however, ‘here’ is not working. More

Striped by its rings’ shadows, Saturn (light blue; artificially coloured) looms behind its moon Mimas (grey sphere), which conceals a liquid ocean underneath its surface.Credit: NASA via Alamy

There’s a newfound ocean in the outer Solar System, and it’s in a very surprising place1. Mimas, a mid-sized moon of Saturn, turns out to have an ocean beneath its icy surface — despite looking too geologically inert to have water sloshing inside.Mimas joins a growing list of icy moons that are also ocean worlds. The fact that boring-looking Mimas has an ocean means that “you could have liquid water almost anywhere”, says Valéry Lainey, an astronomer at the Paris Observatory.That’s important because interactions between ocean water and rock, which would occur where a buried ocean meets a moon’s rocky core, can generate enough chemical energy to sustain living organisms. If there are more stealth ocean worlds out there similar to Mimas, there are greater chances of extraterrestrial life.Peek-a-boo oceanThe discovery, reported today in Nature by Lainey and his colleagues, largely resolves the long-standing question of whether Mimas has an ocean. Many researchers hadn’t expected it to: Mimas’s geology does not display signs of a possible buried ocean, such as the icy rafts that jostle on Jupiter’s moon Europa or the geysers that spew from Enceladus, another icy moon of Saturn.
Pluto’s dark side spills its secrets — including hints of a hidden ocean
But in 2014, a team that included Lainey and that was led by Radwan Tajeddine, an astronomer then at the Paris Observatory, analysed images taken by NASA’s Cassini spacecraft, which explored Saturn and its moons between 2004 and 2017. By studying how the 400-kilometre-wide Mimas wobbled in its orbit around Saturn, the researchers concluded that it had either a buried ocean or a rugby-ball-shaped core2. As more scientists studied how an ocean could have formed and evolved, it became harder to explain the geology of Mimas without invoking an ocean3.In the 2024 study, Lainey and his colleagues seem to have nailed the case. They went further than they had in 2014, by analysing not just the orbit’s wobble but also how Mimas’s rotation around Saturn changed over time. The team combined Cassini observations with simulations of Mimas’s interior and its orbit to conclude that there must be an ocean 20–30 kilometres below Mimas’s surface.Solid evidenceThe work is the best evidence yet for an ocean in Mimas, says Alyssa Rhoden, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who will report similar conclusions at a conference next month in Texas. “I am happy to move Mimas from the ‘maybe possibly an ocean world’ category to the ‘yeah it really could be an ocean moon’ category,” she says.
Cassini’s 13 years of stunning Saturn science — in pictures
But it seems to be a young ocean — having formed in the last 25 million years, compared with almost 4 billion years ago for Earth’s first ocean. If the ocean had been around for longer, it would have begun to exert its influence on Mimas’s icy surface by now, for example by fracturing it. At some point in the recent past, Lainey says, Mimas was probably travelling on a stretched-out orbit that caused it to gravitationally interact with other Saturnian moons. That tidal interaction would have heated up Mimas, melting its interior and creating the ocean.Ultimately, the pockmarked Mimas could evolve to look similar to smooth Enceladus, which is coated in ice created by water spraying through cracks in its shell. And beyond Saturn, the discovery suggests that several moons of Uranus could also be hiding oceans of their own, despite looking static and frozen on their surfaces.“There are no boring moons,” Rhoden says. More

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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