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A storm dumps snow on California’s Mammoth Lakes on 28 March.Credit: Mario Tama/Getty

Not again! Earlier this week, California was battered by heavy rain, strong winds and thick snow — the latest in a seemingly unending procession of strong storms. Wild weather has afflicted the previously drought-stricken state for three months, resulting in devastating floods, paralysing blizzards and dozens of deaths. Data released Thursday show that the snowpack is the biggest on record. Nature spoke to atmospheric and climate scientists about what’s driving the surge in wet weather and what the state could look like in a warmer future.

A rare snowstorm in southern California frosted the mountains on the edge of Los Angeles on 1 March.Credit: Ringo Chiu./ZUMA Press Inc/Alamy

Why are so many storms hitting California?California’s recent parade of storms is driven by atmospheric rivers — long, narrow plumes of moist air that travel from the tropics to higher latitudes. When these ‘rivers in the sky’ sweep over mountainous regions they condense into clouds that produce heavy rain and snow, says Allison Michaelis, an atmospheric scientist at Northern Illinois University in DeKalb.An atmospheric river can ferry enormous amounts of water vapour; some discharge more than twice as much water as the Amazon River1. In the western United States, atmospheric rivers contribute up to half of the region’s annual rain and snow. Since last November, 31 atmospheric rivers have hit California, more than half of which ranged from moderate to extreme, according to data from the Scripps Institution of Oceanography in La Jolla, California.Although back-to-back atmospheric rivers are not unheard of, they make a significant impact, says Michaelis. “What might have typically been a more beneficial event could turn potentially hazardous if it comes on the heels of another system.”

Cars dot floodwaters from the Tule River on 21 March, after days of heavy rain in Corcoran, California.Credit: David Swanson/Reuters

How much snow is there?In the Sierra Nevada mountain range in eastern California, the season is the snowiest since 1952, says Andrew Schwartz, an atmospheric scientist who leads the University of California, Berkeley’s Central Sierra Snow Lab in Donner Pass. “It’s just dumping snow,” he says. A total of 18 metres of snow has fallen at the lab this season, nearly double the yearly average. And statewide, the snow’s water content — the amount of water that would result if the snow were melted — is roughly double the average, says Schwartz.The conditions have brought welcome relief after the three driest years on record in California, allowing the rollback of ‘exceptional’ and ‘extreme’ drought designations for the first time since 2020, according to the US National Oceanic and Atmospheric Administration’s US spring outlook. But capturing and storing water released as the thick snowpack begins to melt can be a race against time, says Tom Corringham, a research economist at Scripps. If the snow melts too quickly, the excess water ends up in the ocean instead of being stored and distributed to where it’s needed most, he says. “That’s not ideal for water management.”

People remove snow from a residential complex in Mammoth Lakes, California, on 29 March.Credit: Mario Tama/Getty

Is climate change playing a part?As the atmosphere warms, atmospheric rivers are likely to become more frequent and hold more moisture, and that will result in heavy downpours of rain and snow, says Schwartz. He notes that California is swinging between wet and dry periods that are more extreme than in the past. “While this variability has always existed, it’s becoming amplified due to climate change,” he says.Kim Reid, a climate scientist at Monash University in Melbourne, Australia, says that more work needs to be done to understand how climate change will affect jet streams and other systems that influence the direction of atmospheric rivers. If atmospheric rivers shift by a few degrees latitude, they could become more common in some regions and rarer in others, she says. More

Baghdad on the Tigris: this week Iraq became the first country in the Middle East to join the UN water convention.Credit: Getty

Forty-six years. That’s how long it took the United Nations to organize a high-level conference on water. The 3-day event, held last week in New York, was brief compared with its 12-day predecessor, which took place in Mar del Plata, Argentina, in 1977. That meeting helped to catalyse the drafting of the UN’s 1992 water convention, an international agreement through which countries agree to cooperate on the use and protection of shared waterways. Delegates to this month’s conference did not make any binding commitments, but countries are converging on several ideas. One is to establish a panel of scientists to regularly advise on water issues. Another is for the UN to appoint a ‘water envoy’, a high-level diplomat representing secretary-general António Guterres. The conference also increased the visibility of the 1992 convention.Each of these is an important step. The appointment of a UN envoy would send a powerful signal that this is a hot topic, high on the agenda of world leaders, and that a boost to the science is overdue. For decades, there’s been much rhetoric around applying science to water resources at the intergovernmental level, but action has been piecemeal. The 1977 conference report (known as the Mar del Plata Action Plan) and the 1992 convention recognize the need for research and development. This need was most recently incorporated into the UN’s Sustainable Development Goals (SDGs) in 2015; SDG6 aims to achieve equitable access to safe water and sanitation by 2030. These agreements also mention the need for countries to share data — for example, on river flows, weather and climate, and water quality. But with some two billion people still lacking safe water in their homes, SDG6 is a long way from being achieved.
The world faces a water crisis — 4 powerful charts show how
The necessity of studying and sharing such data is underscored by a Comment in Nature written by climate scientist Johan Rockström, economist Mariana Mazzucato and their colleagues. Among other things, they describe how land-management practices in one country can impact atmospheric water flows in other countries. But to properly take advantage of such knowledge, countries need to both collect and share data.One option proposed by the UN’s science agency UNESCO is modelled on the Intergovernmental Panel for Climate Change, and would produce periodic global literature reviews to be signed off by governments. Such an idea needs rigorous analysis and testing. Separately, there is also a real need for input from independent scientists on water disputes between nations.At the start of the year, Mohammed Basheer, a water-resources economist at the Humboldt University of Berlin, and his colleagues published a modelling study addressing a protracted dispute over Africa’s largest hydroelectric dam on the Nile River. The work showed how Egypt, Ethiopia and Sudan, the three countries involved, could benefit if each was willing to compromise (M. Basheer et al. Nature Clim. Change 13, 48–57; 2023). However, it’s not clear whether these recommendations will find their way into negotiations. Relations between Egypt and Ethiopia are fraught, and there is no clear path for the provision of independent scientific advice on the dam.
Why we need a new economics of water as a common good
A study by Patience Mukuyu at the International Water Management Institute in Pretoria, South Africa, and her colleagues, published in early March, reaffirms that relatively few countries that share watercourses are cooperating, such as by sharing data (P. Mukuyu et al. Water Int. https://doi.org/j36p; 2023). Co-author Alistair Rieu-Clarke at Northumbria University, UK, who studies transboundary water issues, emphasizes that there are demonstrable benefits to data sharing. In September 2021, four African countries — Gambia, Guinea Bissau, Mauritania and Senegal — agreed to cooperate (including by sharing data) on a giant underground aquifer, which covers more than 300,000 square kilometres and supplies water to 80% of their combined populations.The list of transboundary water disputes is lengthening. The Indus Waters Treaty, a 63-year-old agreement between India and Pakistan on sharing the Indus River’s waters, is in trouble. The melting of glaciers as a result of climate change is affecting river flows; at the same time, both countries have plans in the works to build dams. In January, India announced that it wants to renegotiate the treaty to take account of a changed environmental and geopolitical situation, rather than work within what it sees as an outdated framework. However, Pakistan wants to continue to resolve disagreements using the treaty’s dispute-settlement procedures. Elsewhere, Iran, Iraq, Syria and Turkey have long been at odds over the shared Euphrates–Tigris river basin, where water availability will also be affected by climate change.The idea of a UN water envoy and science panel offer an opportunity to make a difference to such disputes. More countries that share water resources also need to sign and ratify the 1992 UN water convention. Last week, Iraq, Nigeria and Panama were among ten countries to either do so or announce that they intend to do as much.The UN and its member states have made a positive start. Increased visibility of the 1992 convention will pay dividends, as will boosting research to help policymakers to better understand and resolve water crises, although the devil will be in the detail. Science, as Basheer told Nature earlier in the year, can show countries how to “help each other, look after each other and look out for each other”, when water disputes are being discussed. Ultimately, countries need to accept that scientists must have a seat at the table during these discussions. More

Water is the lifeblood of our planet — essential for keeping humans and every plant and animal alive. It helps to circulate carbon and nutrients in the air and in soils, and regulates climate. For millennia, Earth’s water cycle has provided reliable supplies and sustained conditions conducive to human development. Yet anthropogenic pressures are now pushing the cycle out of balance, threatening to undermine the reliability of rainfall itself.The impacts are already being felt across the world — in devastating floods, such as those in Pakistan last year that killed 1,500 people and affected two-thirds of the country’s districts, and in severe droughts such as the five failed rainy seasons in a row that have brought more than 20 million people to the point of starvation in the Horn of Africa. Meanwhile, more than 2 billion people still lack access to safe drinking water, one child dies every 17 seconds from waterborne diseases, and 3 billion people face food insecurity owing to water scarcity — numbers that could grow with the global population unless water provision improves (see go.nature.com/3jkgtry).Water managers have always had to deal with natural variability, building larger reservoirs and tapping aquifers to fight scarcity, for example. But current challenges and trends in the rest of this century demand a completely different approach: a radical shake-up in how water is governed, managed and valued, from local to global scales, including a re-evaluation of human water needs (see Supplementary information, Box S1).Today, the sector concentrates on flows of ‘blue’ fresh water — liquid that runs off the land and is stored in rivers, lakes, reservoirs and underground aquifers. Utilities capture and extract this water locally for drinking and sanitation, agricultural irrigation and industry. They assume it will be continually replenished, naturally, within historical ranges. In many places, that premise already no longer holds.
As the UN meets, make water central to climate action
Each 1 °C of global warming increases global mean precipitation by 1–3%, and it could rise by up to 12% by the end of the century compared with the period 1995–20141. The impacts will be felt unevenly, with the frequency and severity of both floods and droughts rising. Deforestation, land degradation and infrastructure development are also altering precipitation patterns and affecting where water comes from and ends up2. Excessive extraction for irrigation and industry is aggravating water shortages in river basins, from the Colorado in the United States and the Yangtze in China to the Murray–Darling in Australia.To meet these growing challenges, water must be recast as a global common good. That means states establishing an obligation under international law to protect the global water cycle for all people and generations, and acknowledging that actions in one place have impacts in another — for instance, that deforestation in Brazil affects rainfall in Peru. It means assessing the role and economic value of not just blue fresh water, but also ‘green’ water that is held in the air, biomass and soils. And it means governments and the private sectors reformulating their roles and responsibilities, to develop objectives, policies and funds that can reshape markets and better manage global water supplies.All these challenges must be discussed at the United Nations Water Conference in New York this week — the first such meeting in almost 50 years. Here, we highlight three areas in which research is badly needed to support discussions.Understand all water flows within and between nations fullyManaging fresh water on a global scale means going beyond our current fixation on capturing blue water, which constitutes 35% of all fresh water on land, to also encompass green water, which makes up the remaining 65% (see Supplementary information, Fig. S1). Flows of moisture and vapour from land and vegetation are essential for regulating the water cycle and securing future rainfall, as well enabling carbon sequestration in soils and forests.Globally, up to half of terrestrial precipitation originates from green water evaporated over land, with the rest from evaporation over the ocean3. Thus, landscape changes can alter water supplies in regions downwind, as well as changing local climates and streamflows. For example, deforestation in the Congo Basin lowers rainfall in neighbouring countries, and even across the Atlantic in the Amazon. Heavy irrigation of crops in India can boost the streamflow of the Yangtze River in China, through moisture transported downwind4.
Flash floods: why are more of them devastating the world’s driest regions?
By analogy with watersheds on land, researchers refer to ‘precipitationsheds’ and ‘evaporationsheds’ in the atmosphere. Simply put, a precipitationshed is where rain comes from and an evaporationshed is where evaporation goes to. (Here, evaporation refers to total evaporation from the ocean and green water flows from land, including from soil and water bodies, as well as transpiration from vegetation.)Researchers need to understand better how these processes interact and how atmospheric flows of water vapour connect different regions. A new view of interconnectivity is emerging, through combining meteorological databases (including on water vapour, humidity, wind speed and direction) and computer models that connect likely sources and sinks.To illustrate, we used such data3,5 to calculate volumes, ratios and flows of evaporation and precipitation in several regions (see ‘Atmospheric watersheds’, ‘Terrestrial moisture flows across borders’ and Supplementary information, Fig. S2). Generally, countries where prevailing winds blow from the ocean have a plentiful and consistent source of moisture and little dependence on other nations. Landlocked countries are more vulnerable to natural variability and the practices of neighbours over which they have no control.

Source: Analysis by J. Rockström et al.

For example, Brazil is largely self-sufficient in green water and precipitation. We find that around 60% of its rainfall comes from moisture evaporated from the Atlantic, and 35% from moisture from Brazilian lands, including the Amazon rainforest (see Supplementary information, Fig. 2a). Much of this airborne moisture stays within the country, trapped by the High Andes. But Brazil also exports 25% of its green water to downwind countries, such as Argentina, Bolivia and Colombia. Rainfall in these nations will drop if deforestation in the Amazon continues6, yet no political or institutional arrangements exist to address this dependency.Rainfall patterns in sub-Saharan Africa, meanwhile, are tightly interwoven. Nigeria derives 64% of the moisture that precipitates its rainfall from within the continent; of this, 22% comes from within and 42% from outside its borders, predominantly from the Congo Basin. In turn, Nigerian land contributes 43% of the evaporated water driving rainfall in neighbouring countries such as Cameroon, Guinea and Ghana. All these countries’ water supplies are thus at risk from deforestation in central Africa.China, too, is heavily reliant (74%) on water evaporated from land for its precipitation. Of that, 44% comes from internally recycled moisture, and the rest from upwind neighbours, including India, Kazakhstan and Russia. Moisture from Chinese land also has a large role in rainfall across Central Asia and the Tibetan Plateau.Moreover, no country acquires over half of its moisture from within its own boundaries, implying that even the largest countries rely on evaporation from other areas to sustain their precipitation. Even Russia, the most self-reliant in rainfall and with 45% of its moisture recycled internally (see Supplementary information, Fig. S2a), is still heavily dependent on neighbouring countries (20%) and the ocean (35%).

Source: Analysis by J. Rockström et al. See also Fig. S2b in the supplementary information.

This striking view of interdependence surpasses existing transboundary issues around rivers, lakes and groundwater, which are the usual focus of water governance and disputes. For example, the Grand Ethiopian Renaissance dam on the Blue Nile has an impact on supplies to Sudan and Egypt downriver. Researchers need to study how rifts between countries might grow once inter-reliance is better understood.To inform policies, scientists need to assess water stocks and flows of green and blue water, locally and globally, using satellites, big data and Earth-system models. Researchers need to know where and through which processes global change is shifting freshwater cycles and supply. The impacts and costs of extreme events, such as parching of soils and extremes of river flow, need to be studied in the context of precipitationsheds and evaporationsheds.Hydrologists, economists and political scientists will need to set budgets for green and blue water across scales, while keeping the sources and patterns of fresh water within ranges typical of the past 12,000 years during which human civilizations evolved (the Holocene epoch). However, recent analyses suggest that features such as soil moisture are already deviating from historical ranges in some places, being either wetter or drier7.Rethink how water is valued and who ‘owns’ itTreating water as a collective resource requires rethinking its economics. Currently, blue water is managed and regulated largely as a public good for drinking and sanitation. Yet public ownership undervalues water, in that one person’s access does not limit another’s, even though water is a finite resource. This promotes excessive, unsustainable and inequitable use. And it discourages private investment. In 2015, private-sector investment in water globally accounted for less than 5% of the total funds allocated to telecommunications, energy, transport and other basic services8.
Degrowth can work — here’s how science can help
By contrast, green water is given no economic value, despite the fact that it drives economic development, stabilizes climate change and secures precipitation. It can be public, private or a common good, depending on where it is.To manage both blue and green water as a global common good, governments need to reshape water markets — not simply fix them when they fail. Governments must monitor soil moisture and vapour flows, and set policies that value these flows as natural capital. Water governance and management need to span all scales, connecting local watersheds, river basins, precipitation- and evaporationsheds, and eventually the globe.To bring in businesses and investments, economists need to value water as an asset that generates functions and services for human well-being. This could follow, for example, the framework established in the Dasgupta Review on the economics of biodiversity, published by the UK government in 2021 (see go.nature.com/2om5hho), which sets value on natural capital and manages natural assets within a sustainability framework. Researchers must evaluate the amount of green water needed to sustain biodiversity and carbon sinks in ecosystems. And they must assess the ‘social cost of water’ (akin to the ‘social cost of carbon’), which considers the costs to society of loss and damage caused by water extremes and not meeting the basic provision of water for human needs.

Access to clean drinking water remains a global problem, one that could worsen as the world’s population continues to rise.Credit: Ashraf Shazly/AFP/Getty

Whenever private companies benefit from public subsidies, guarantees, loans, bailouts and procurements, governments could attach conditionalities to contracts to maximize public benefits. For instance, the 1996 amendments to the Safe Drinking Water Act in the United States promoted equitable access to water by creating the Drinking Water State Revolving Fund to subsidize companies that provide water for disadvantaged communities. Similarly, the 2022 US CHIPS and Science Act contractually obliges funding recipients to maximize efficiency with regard to water, waste and electricity.New forms of public–private arrangements, including permits, property rights and procurements, should be developed to counteract the rent-seeking and value-extractive behaviour that has plagued some national water sectors. In England, for example, since the privatization of the water industry in 1989, £72 billion (US$88 billion) has been paid out to shareholders as dividends, while outdated infrastructure has left the water system riddled with leaks and sewage discharges.Some preliminary work to reshape the economics of water has begun: two of us (M.M. and J.R.) are leaders on the independent Global Commission on the Economics of Water (watercommission.org), which was launched in May 2022 at the World Economic Forum in Davos, Switzerland. The group is assessing impacts on the global hydrological cycle from climate and environmental change, as well as country interdependencies and the international cooperation needed to treat water as a global common good. A call to action (see go.nature.com/3zxnw54) and a first review report (see go.nature.com/3twxsok) were released the week before the UN 2023 Water Conference.Start locally and build globallyEffective management of water as a global common good starts locally. National governments, cities and regions need to define goal-driven ‘missions’ that add up globally. For example, nations might pledge to ensure that the supply of green and blue water in the hydrological cycle inside their borders remains within a manageable range, as defined by safe planetary limits or boundaries9. Targets and strategies must be designed to initiate coordination, finance and innovations10.For example, the European Union’s Water Framework Directive has, since 2000, required the EU member states to develop river-basin management plans jointly with the public. Obligations are reviewed every six years, and non-compliance brings legal sanctions. Although progress has been made, more-coordinated efforts and monitoring would help to realize the directive’s full potential11.All sectors must be involved. Food production, for example, accounts for around 75% of freshwater consumption globally, with India the largest consumer. India might, for instance, focus on ensuring continuity of food supply without imposing pressures on national use of green and blue water. Production and consumption processes should be redesigned to minimize water waste and maximize water sharing.In Australia, the national science agency, CSIRO, is working to reduce the economic impacts of the country’s droughts by 30% this decade, by making climate data accessible to farmers to enable them to make informed water-use decisions. Other countries, such as Kenya, are exploring ‘green water credits’ that reward upstream water management beneficial to downstream areas12.Cooperation and exchange of knowledge will be crucial to join up local and global strategies. As with greenhouse-gas accounting and the Sustainable Development Goals, the UN and other bodies will need to develop mechanisms for overseeing the planet’s water resources; discussions on how to do that must start this week in New York City. None of what we set out here will be easy. But the future of Earth’s bloodstream is at stake. More

As many as 43,000 people might have died as a result of drought in Somalia last year, according to a report published this week by the Somalian government, the UN children’s agency UNICEF and the World Health Organization.Credit: Jerome Delay/AP/Shutterstock

The United Nations water conference starts tomorrow. Co-hosted by the Netherlands and Tajikistan, the three-day event will take place at UN headquarters in New York and will be the first such event in nearly half a century. During that time, a rising number of people around the world have gained access to safe water and sanitation (see ‘A tale of two halves’) — except in sub-Saharan Africa (see ‘The neglect of Africa’), where the numbers without safe drinking-water services are greater than they were in 2000. Globally, around 500 million people are compelled to use open defecation, and millions more rely on contaminated water supplies. Can this conference make a difference?

Source: WHO/UNICEF

Why has it taken the United Nations 46 years to organize a conference dedicated to water?The simplest answer is that water (as a standalone topic) has not been high on the international sustainable-development policy agenda — at least, not until now, says Rachael McDonnell, deputy director-general for research for development at the International Water Management Institute, based in Rome.The first UN water conference took place in Mar del Plata, Argentina, in 1977. Representatives of 118 countries and territories met over 12 days and issued the Mar del Plata Action Plan, which recommended that countries achieve universal clean water and sanitation by 1990 to avoid a global water crisis by the end of the twentieth century.Several low-income countries asked for financial support, but were rebuffed, and instead a study was proposed on how to finance water projects, as Nature reported at the time.In 2015, the international community set a 2030 target (under the UN Sustainable Development Goals, SDGs) for providing clean water and sanitation to all. As of 2020, some 2 billion people still lacked safe drinking water in their homes, and around one-third of people did not have basic handwashing facilities at home, according to data from the World Health Organization (WHO) and the UN children’s agency UNICEF. At current rates of improvement, 1.6 billion people will still lack safe drinking water at home by the 2030 deadline.

Source: WHO/UNICEF

Water was not a priority for the September 2021 UN conference on food security, nor last year’s climate COP27 in Egypt, says Henk Ovink, the Netherlands’ special envoy for international water affairs. Water must have a firm place in any follow-up UN process, he stresses. These include the UN Food Systems Stocktaking Moment that will take place in Rome in July, the SDG Summit in September in New York, and COP28 in Dubai in November. “We can’t wait another 46 years because what is happening is just too awful at the moment, and it’s going to get worse,” says McDonnell.Where is the crisis at its worst?The water crisis is worst in low-income countries — for example, an estimated 70% of the population of sub-Saharan Africa lacks safe drinking-water services.The conference needs to prioritize addressing water insecurity in vulnerable communities and those in conflict and post-conflict settings, says Carol Cherfane, director of the Arab Centre for Climate Change Policies, a think-tank connected to the UN based in Beirut. A report published this week by UNICEF and the WHO says that as many as 43,000 people might have died last year from drought in Somalia (see ‘Scorched Earth’).

Source: IPCC

Providing better access to water for health care and sanitation is another urgent priority. Too many people have no choice but to use contaminated water supplies (see ‘Faecal contamination’). In 2021, one in 10 health-care facilities worldwide had no sanitation services and some 857 million people had no water service at their health-care facility, according to an earlier joint report also by the WHO and UNICEF summarizing 20 years of data on water and sanitation.The conference will also discuss a plan for countries that share their water resources to communicate more effectively. The Transboundary Water Cooperation Coalition was launched at the Paris headquarters of the UN science agency UNESCO at the end of last year. This will be particularly important for countries in the Middle East and North Africa. Around two-thirds “of the water resources in Arab states flow from outside of their national borders”, says Cherfane. “A transboundary basin-level approach is very important, not as an instrument of creating conflicts, but as an instrument of creating opportunity for conversations and cooperation and coordination.”How is climate change affecting water resources?Around half of the world’s population is already at risk of severe water scarcity for at least some of the year, according to the latest (sixth) assessment report from the Intergovernmental Panel on Climate Change, published this week. This number is likely to increase owing to the effects of climate change, such as heavy precipitation, flooding, drought and wildfire events. If global temperatures reach 1.5°C above pre-industrial temperatures, extreme agricultural (soil moisture) drought is expected to be twice as likely in many parts of the world.

Yahia Abdel Mageed, Sudan’s then-irrigation minister, was secretary-general of the first UN water conference in 1977. Calls at that meeting for financial help for low-income countries were rebuffed.Credit: Keystone Pictures USA/Zuma Press/Alamy

Will the conference lead to a legally binding water treaty?The conference will produce a ‘water action agenda’. But this will involve “voluntary commitments”, says McDonnell. “There’s nothing binding, there is no equivalent to the Paris [climate] agreement.” Moreover, there’s no leading UN body that is responsible for implementing and monitoring progress for all water-related SDGs. “The conference finds itself in an institutional void,” says Ovink. “While we are now very busy with the water conference, we’re not very busy with water.”But setting up a new treaty or institutional UN body will take many years. Instead, delegates will call for water to be prioritized in existing treaties and in the UN system.Some countries will be calling for more funds, especially in the form of grants for projects such as desalination of seawater or wastewater treatment. Much existing international support is loans, says Omar Salameh, a spokesman for Jordan’s water and irrigation ministry, based in Amman. “However, loans exacerbate the financial pressures on already-struggling economies,’ he says.UN secretary-general António Guterres is also expected to ramp up fundraising for his plan, announced at COP27, to create climate early-warning systems in all UN member states, so that countries are better prepared for extreme events. “Only half of our 193 members have proper early-warning services in place,” says Petteri Taalas, secretary-general of the World Meteorological Organization, based in Geneva, Switzerland, which is working with Guterres to implement the plan. “We need some US$3 billion during the coming five years,” adds Taalas. So far, around 10% of this has been raised, through different sources.

Source: WHO/UNICEF More

Perfluorinated and polyfluorinated alkyl substances (PFAS) have been found in more than 2,800 US communities.Credit: Alexander Safonov/Shutterstock

The US Environmental Protection Agency (EPA) has proposed the first limitations on a set of pervasive and dangerous ‘forever chemicals’ in US drinking water. The chemicals, known for their strong carbon–fluorine bonds, are difficult to destroy and have become widely dispersed in the environment. Scientists and engineers are busy developing ways to extract the chemicals more efficiently from water and soil and break them down, but water utility companies warn that meeting the EPA’s new standards will be expensive in the short term — possibly prohibitively so for small water-treatment facilities.“This is a huge deal, in terms of protecting public health, but also in terms of what it’s going to take to accomplish,” says Michelle Crimi, an environmental engineer at Clarkson University in Potsdam, New York.
Tainted water: the scientists tracing thousands of fluorinated chemicals in our environment
Proposed on 14 March, the regulation targets perfluorinated and polyfluorinated alkyl substances (PFAS), a class of thousands of nearly indestructible compounds used in everything from non-stick cookware and waterproof clothes to industrial materials and cosmetics. Once called miracle chemicals for their hallmark durability, PFAS accumulate in the environment and in people; even minute amounts increase the risk of cancer, as well as the risk of developmental and other health problems1, research shows.The EPA suggested a voluntary limit for PFAS in drinking water in 2016, but this is the first time it has advanced a mandatory requirement. The core of the proposal would restrict two of the most dangerous PFAS compounds, PFOA and PFOS, to four parts per trillion. That is the lowest level that is detectable using current laboratory tests, although the agency has determined that there are risks associated with much lower concentrations. Another four chemicals would be regulated as a mixture.Similar movements to rein in PFAS are afoot internationally. At the extreme end of the spectrum, the European Union is considering legislation that would ban the production of PFAS altogether.Health costsAchieving the EPA’s proposed regulation won’t be cheap. PFAS contamination has been found in around 2,800 communities in the United States, according to the Environmental Working Group, an advocacy organization based in Washington DC, and research by the group suggests that it probably affects the water supplies of at least 200 million people2. And although the use of PFOA and PFOS has mostly been phased out in the United States, the group has identified around 30,000 industrial facilities that could be using countless other compounds in the PFAS family.
How to destroy ‘forever chemicals’: cheap method breaks down PFAS
Numerous states have already set limits on PFAS in drinking water, and water providers have demonstrated that existing technologies such as carbon filtration can reduce PFAS amounts to undetectable levels. But installing such technologies nationally could be costly, with the financial burden falling disproportionately on smaller water-treatment systems. For facilities large and small, adding PFAS filtration will have to be weighed against other priorities, such as replacing lead pipes, says Chris Moody, a regulatory analyst with the American Water Works Association (AWWA), which is based in Denver, Colorado, and represents more than 4,300 utility companies that provide some 80% of the US drinking-water supply.By one measure, the EPA estimates that implementing its proposal nationally would cost around US$772 million annually, but a study commissioned by the AWWA using similar assumptions suggests that the price tag could be around $2.9 billion a year. The EPA says that more than $9 billion is already available through a US infrastructure law enacted in late 2021, but Moody stresses that this is just a start: the AWWA-estimated cost over 20 years is $58 billion.If history is any indicator, however, costs will probably come down over time, says Melanie Benesh, vice-president of government affairs at the Environmental Working Group. “With regulation often comes market innovation,” she adds.Innovative solutionsScientists and engineers started investigating technologies years ago, when the risks posed by PFAS became clear. Research has focused on methods to more efficiently remove PFAS from drinking water, clean up groundwater contamination or destroy the chemical compounds.The upshot is that a variety of promising technologies are now available, from carbon filtration and ion-exchange systems that can separate PFAS from drinking water to electrochemical and gasification methods to break down PFAS, says Patrick McNamara, an engineer at Marquette University in Milwaukee, Wisconsin. But scaling them up to be practical could be challenging, he adds.For her part, Crimi is working with the US Department of Defense to test a technology that could be used to clean up plumes of PFAS contamination in groundwater before they leach into drinking-water supplies. Starting as early as this year at Peterson Space Force Base in Colorado Springs, groundwater will be collected inside a horizontal well and funnelled through a reactor developed by Crimi’s team that uses ultrasound waves to break the carbon–fluorine bonds in PFAS3.“We know it’s effective in the lab,” she says, but there are always things to learn when scaling up to field operations.The EPA is accepting comments on the proposal until mid-April. More

Competing interests
J.H.M. worked as an advisor to the Asian Development Bank and World Bank on water and climate change issues. He is currently working with a coalition of national party, private sector, and NGO groups on a set of cases and recommendations to articulate water resilience as an operational economic concept, which is funded by the Kingdom of the Netherlands, GIZ, and the Kingdom of Spain. More

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