Sorbent materials that capture and release water molecules are key to technologies that turn the Earth’s ambient moisture into drinkable water and energy.

As climate change pulls Earth to greater extremes, it is widening existing inequalities and threatening a just future. One of the most pressing concerns is access to fresh water. Water is not only essential for survival, but it is also deeply tied to prosperity1. Yet water distribution is profoundly uneven, and the gap between the water secure and water insecure is growing as floods and droughts become more common and severe.

At the same time, demand for indoor cooling and heating, which already accounts for about a quarter of global energy use2, will continue to surge as climates intensify3. More energy demand means more greenhouse gas emissions, raising temperatures in a ruthless feedback loop. Heatwaves are now a serious public health concern, especially for those who cannot afford or lack access to air conditioning, or who live in urban heat islands where dense infrastructure traps heat.

In all of these cases, the world’s most vulnerable populations — including remote and Indigenous communities, those in low-income regions and people living in poverty — will bear the brunt of these shifts.

Amid these crises, there is a largely untapped resource that could help redistribute access to water and energy. Water molecules are present in the air around all of us, whether we are in the rainforest or in the desert. In fact, the Earth’s atmosphere contains an estimated thirteen quadrillion (that’s 13,000,000,000,000,000) litres of water at any time, mostly in the form of vapour that is continuously replenished by the global water cycle. As Fredrik Edström and Per Dahlbäck suggest in their Comment in this issue, this vast, decentralized reservoir of moisture may be the key to democratizing clean drinking water and unlocking new energy sources — if we can learn to draw upon it.

In this Focus issue, we highlight a class of materials — sorbents — that are uniquely able to transform this ambient moisture into critical resources: drinkable water, thermal energy and even electricity. Sorbents capture water vapour from the air spontaneously, without needing energy input (a process called sorption). When heated slightly, using sustainable sources like solar energy or waste heat from photovoltaic panels, these materials release the water that they have captured (desorption). The articles in this issue explore how sorbent materials are central to harnessing atmospheric water.

Turning humidity into safe drinking water may seem like an obvious solution to water scarcity, but the technology to achieve this is far from simple. For years, atmospheric water harvesting (AWH) technologies either collected tiny droplets from fog (requiring misty climates) or cooled air below its dew point (requiring lots of electricity). Both approaches are impractical or downright impossible in arid, remote or low-income regions, let alone on a global scale.

In 2017, we got a glimpse of a sorption-based AWH device that could harvest water from bone-dry desert air, using only a thirsty metal–organic framework and sunlight to capture and release the water molecules4. Off-grid operation across a range of humidity levels has since made sorption-based AWH the foundation for various water-harvesting systems now being developed, commercialized and implemented in water-stressed and isolated regions. An especially promising use case is in post-disaster zones, where these portable devices can be quickly set up to provide immediate access to clean water.

But the tech is still far from addressing water scarcity on a global scale. To scale up water production, chemists and materials scientists will need to innovate at the sorbent level, and engineers will need to configure devices and systems that push the technology’s thermodynamic limits. In this issue, a Review by Swee Ching Tan, Ruzhu Wang and colleagues introduces a materials design framework to optimize the performance of sorbents, and a Review by Evelyn Wang, Lenan Zhang and colleagues connects design and engineering decisions across all relevant length scales — molecules, materials, devices, systems and the globe — to close the knowledge gaps limiting the technology’s real-world impact.

Atmospheric water, when paired with sorption processes, can also be a renewable source of both thermal and electrical energy, as examined in a Perspective in this issue by Tingxian Li, Liangti Qu, Ruzhu Wang and colleagues. Thanks to basic thermodynamics, sorption releases heat and desorption takes it in, which heats or cools the surroundings, respectively. Water captured by an ionizable sorbent can create a voltage and current through the material, producing electricity.

Although the ability of sorption–desorption to convert and store heat has long been a hallmark of thermal engineering, using ambient moisture as the driving source has pulled the field in a new, sustainable direction. Buildings contribute enormously to carbon emissions as they suck energy for cooling, heating, appliances and lighting. Installing sorbents in roofs and walls as a passive energy source may help reduce buildings’ reliance on fossil fuels. It may even enable indoor climate control and electrify devices in communities off the grid.

Ultimately, using Earth’s moisture is only a part of the broad effort needed to achieve a more equitable future. Big questions remain, such as how drawing water from the atmosphere might impact the planet’s greenhouse effect or water cycle; these will need decisive answers as the technology develops. But for now, sorbent materials give us hope that a key resource we have been looking for has been in our midst all along.