This oasis (above) next to the town of Mao, Chad, allows farmers to grow date palms and cultivate a few crops in the small fields around it. But rising temperatures due to climate change are a growing threat to oases such as this, and to the people and wildlife that depend on them.

The image is part of a series shot by photographer Tommy Trenchard for the photo essay “, which explores how these fragile ecosystems are disappearing. As temperatures rise, vegetation is retreating around oases and sand dunes are encroaching upon them. To try to hold back the sands, farmers in villages such as Kaou, also in Chad, are building barriers from palm fronds, as shown in the images below.

Mao and Kaou are located in the Sahel region, the semi-arid belt south of the Sahara desert that stretches right across Africa, from Mauritania to Eritrea. In 2007, the African Union launched the Great Green Wall initiative to try to prevent the desertification of the Sahel.

As part of this initiative, solar-powered water pumps have been installed in places such as Barkadroussou (below), not far from Mao in Chad, to help farmers irrigate crops. But the Great Green Wall initiative is controversial, with many questioning whether it will work.

Even where measures such as building barriers or installing boreholes do make a difference, with temperatures set to rise higher still, it is far from clear that oases like these will remain oases for much longer.

In the parched terrain of Kenya’s Tsavo East National Park, the spiderweb of animal tracks that splay out from an ancient acacia, known as the Tree of Life, are reminiscent of roots. The scene is a reminder of the fragility of life’s connection to water.

Animals come from far and wide to shelter under the shade of this solitary tree. The most marvellous thing about water is the infinite ways that life responds to it – a tree sends down roots, a canopy grows, animals converge, a landscape is marked.

This image was captured by Yann Arthus-Bertrand, author of the bestselling photo book The Earth from Above, published in 1999. It is included in his new book, (out 11 June), a look at the world through the lens of its freshwater systems, co-written with biologist Bill François.

François says the tree shot is an “iconic picture from Yann’s work”. “A tree can spread 400 litres of fresh water a day in the surroundings by leaves’ transpiration,” he says. “And in its shade, temperature drops by 5°C. The tree is helping underground water reach the surface of the Earth and nurture life, acting as a living water well.”

Freshwater explores the scarcity of perhaps our most precious resource, which can sometimes seem plentiful and limitless. We may think that we live in a water world, but, as the authors point out and the images in the book demonstrate, water – especially fresh water – is actually the thinnest skin on what would otherwise be a barren, dry and lifeless planet.

“Let’s imagine for a moment that all the water on our planet was gathered into a single drop,” they write. This drop would be 1385 kilometres in diameter, representing over a million cubic kilometres of water. “At first glance, this seems enormous, beyond what we can imagine,” they write – yet this is less than the distance from Paris to Rome.

In reality, the sight of this drop of water, illustrated in Freshwater next to the scale of Earth, is sobering. Even more dramatic is the minuscule, full-stop’s worth of fresh surface water – this drop would be a mere 56 kilometres in diameter.

“If Earth were the size of a hot-air balloon, this fresh surface water would fit inside a wineglass. Tropical forests, civilizations, and living beings—from earthworms to giant sturgeons—depend on this small drop, representing less than a thousandth of the total water on Earth,” the authors write.

Below is another shot from Freshwater, of white pelicans in the Djoudj National Bird Sanctuary, Senegal.

“This park is a mangrove ecosystem, so a very important place for many species, at the interface between salt water and fresh water. It plays a particularly vital role for juvenile saltwater fish. Two thirds of fish caught in the world’s marine fisheries have grown in an estuary,” says François.

“Like many other places, this estuary is threatened by the human activities impacts on the river,” he says. “In this case, damming of the river and draining of nearby plains for agriculture led to an overgrowth of water plants that clogged the ecosystem and created a mosquito and water snails invasion.”

Above is another river snapped by Arthus-Bertrand, this time on the Auyán tepui in the Gran Sabana region of Venezuela. Below is his photograph of a waterfall on Bråsvellbreen glacier on Nordaustlandet Island, Norway.

The beauty of fresh water comes from the complex interplay of its molecules’ physics and chemistry. Salt and air dissolve in it; animals can swim in it; ice floats when other frozen substances sink; and it forms a solid, a liquid and a gas. All three of these phases – running rivers, vast and exquisite lakes, glaciers, polar ice caps, storm clouds and fog – have been the playthings of poets and artists for thousands of years.

Like many beautiful things, however, fresh water can also be transient, altering the appearance of a landscape in scales that span seconds as well as millennia. “A drop of water remains in the atmosphere for a short period, about ten days, compared to several thousand years in the ocean,” the authors write. “Therefore, it is quite rare for a drop to have the chance to end up in the sky; this happens on average every 2,737 years.”

Turning seawater into drinking water is so costly and energy-intensive that it’s untenable in most parts of the world, but a Norwegian company is trialling a new approach that could change that. will launch the world’s first commercial-scale subsea desalination plant in 2026, and says its system will cut the cost and energy consumption of the process dramatically.

Global is going up, driven by population growth, climate change and industrial uses like data centres and manufacturing. Meanwhile, fresh water is becoming due to droughts, deforestation and over-irrigation.

Land-based desalination currently produces of the world’s fresh water supply, with over 300 million people relying on this source for their daily water needs. The biggest plants are , where cheap energy makes the technology more feasible and water scarcity makes it more necessary.

The leading technology for desalination today is reverse osmosis. The method pumps seawater through a membrane with microscopic holes that only allow water molecules to pass through, while salt and other impurities get filtered out. The water has to be pressurised to push it through the filters, a process that requires vast amounts of energy.

Flocean’s approach is to plunge water-filtering pods deep into the ocean, separate seawater from salt at depth, then pump the fresh water back up to land. By putting reverse osmosis pods deep underwater, the technology leverages hydrostatic pressure – the weight of all the water pressing down from above – to push the seawater through filtering membranes.

Less pumping means less energy consumption, around a 40 to 50 per cent reduction compared with conventional desalination plants, according to the company. Plus, seawater is cleaner once you get below the (which extends to 200 metres below the water’s surface), which means the water doesn’t require as much pre-treatment before it reaches membranes.

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“It’s fundamentally quite boring down there from a process and engineering perspective,” says , Flocean’s founder and CEO. “It’s the same salinity, temperature, pressure. It’s dark. There’s not a lot of bacteria that can cause biofouling.” The same hydrostatic pressure that pushes water through the membranes also helps disperse the salty brine by-product, which Flocean says is free of chemicals that might harm marine life.

For the past year, Flocean has been desalinating water at a depth of 524 metres at its test site at Norway’s largest offshore supply base, Mongstad Industrial Park. Its commercial facility, called Flocean One, is being built at the same location, and will initially produce 1000 cubic metres of fresh water daily when it launches next year. The operation can then be scaled up modularly by adding more desalination pods.

“Our philosophy is to keep the subsea units the same and scale by multiplication rather than by building ever bigger machines,” says Fuglesang. Scaling up will involve engineering trade-offs at the system level, however. Since more modules will share the same power supply and controls, Flocean’s engineers need to organise power distribution and the permeate manifold – the mechanism that directs purified water from multiple membranes to a single output line – so that scaling up is as straightforward as possible.

“This solution could become viable in suitable locations, providing affordable water if costs decline, but it has yet to be proven at large scale,” says at New York University Abu Dhabi. “Broad municipal deployment likely depends on overcoming technical and economic challenges over several years.”

Cost reductions will be crucial to scale up the technology further, says Hilal, as it is still much more expensive than obtaining fresh water through conventional methods like pulling from lakes or aquifers.

Cleaning and maintaining the membranes will be one of Flocean’s biggest costs. Advances in membrane technology will help; Hilal’s research group is working on electrically conductive membranes that use electricity to repel salt ions and foulants, keeping themselves clean and boosting throughput. The researchers are also exploring ways to recycle single-use plastics into membrane materials, increasing sustainability while further reducing costs. “More durable membranes and high-efficiency pumps can further lower operational expenses, while renewable energy integration reduces power costs,” says Hilal.

Flocean One should start producing fresh water in the second quarter of 2026. If the technology works as planned, it could help Flocean get the backing to build bigger plants elsewhere. “The biggest challenge for us is having perfect alignment,” says Fuglesang. “We need the client, we need government permissions and we need strong financial partners.”