Drop in the ocean

Deep in the Arabian desert, there is a radical solution to the water shortage. From October, a giant solar-powered dehumidifierHot humid air is filtered over cooling coils, where it condenses and is cleaned by ultraviolet light. will extract 6,700 litres of water a day from the air, bringing an endless supply to Masdar in the United Arab Emirates.

This futuristic device highlights one of the world's greatest puzzles. Water is our most abundant natural resource, covering 70% of the Earth's surface. But less than 1% is drinkable - and for billions, it is a rare commodity.

In fact, in many places, it is disappearing altogether.

In Iran, a giant saltwater lakeLake Urmia was once the largest lake in the Middle East. It has shrunk to 10% of its former size and is turning red as its chemical and biological composition changes. has turned red as it dries up. Experts say the country is facing "water bankruptcy" and a "political and economic apocalypse".

Meanwhile, the US is in the grip of a megadrought, unlike anything seen in the last 1,200 years. Mexico's reservoirs are empty and the Parana River in Brazil has fallen to a historic low.

Across Central Asia, a lack of rain has ruined crops and killed livestock. In South Africa, sandstorms have turned farms into wastelands and left 1.35 million people in acute food insecurityWhen a person can not find sufficient food, putting their life or livelihood in immediate danger. Last year, global figures soared to a five-year high at 155 million..

A UN report says climate change is increasing the frequency, severity and length of droughts. And by 2050, the world's population will rise to 10 billion, increasing water demand by 55%. We must plan for a drier world.

Campaigners want us to think about our water footprintLike a carbon footprint, this shows the total volume of freshwater used or polluted to produce the goods and services consumed by an individual or community or produced by a business.. On average 15,400 litres of water is needed to produce 1kg of beef, compared to 4,330 litres for chicken. Cotton is water-intensive, UK researchers are developing a variety that uses 80% less water.

Cities are very inefficient at collecting and consuming water. Newsha Ajami of Stanford University says we must ditch the "one-use system" and recycle grey waterWater used in domestic household waste, including in sinks, baths, showers, washing machines and dishwashers. for use in toilets, gardening and irrigation.

Concrete deserts could be replaced by sponge cities, a Chinese initiative to create urban spaces that harvest water with roof gardens, porous roads and more trees and lakes.

The other option is to tap the water locked away in the sea, ice and air.

For centuries, sailors have distilled saltwater on long voyages. Modern desalination has major drawbacks: it burns a lot of fuel and dumps salty brine back into fragile ecosystems. But newer systems use a technique called reverse osmosisWater is passed through a partially permeable membrane to remove unwanted molecules and participles. which uses significantly less energy.

In Canada, iceberg water is big business. Described as the purest water on Earth, it is bottled from melting sea ice and sold as a luxury product. Critics say this profits from climate change, but there are plans to tow icebergsDrought-stricken Cape Town in South Africa and the UAE are the latest places to consider importing icebergs. Earlier plans by Saudi Arabia in the 1970s and California in the 1940s came to nothing. to Africa and the Middle East.

Unlike sea and ice, air is everywhere. A generator has no transport costs and can be carbon neutral. Similar projects have been used in hospitals in the Gaza Strip, in a Lebanese refugee camp and in villages in Namibia. It could be the thirst-quenching solution for a water-starved world.

Has the world got enough to drink?

Some say yes, there is the same amount of water on Earth as when it was formed. Over millions of years, it is recycled between the atmosphere, surface and the rocks of the inner Earth. At high altitudes, water freezes and falls back to Earth. So it can not disappear or run out, but modern technology allows us to capture, store and use it more efficiently.

Others say no, safe drinkable water is precious and limited. Transporting icebergs to Africa and sucking water from the air shows that something is going seriously wrong with the Earth's hydrologic cycle. As the planet heats up, more water will be locked away in the sea and in the atmosphere. And a growing population will fight over a dwindling supply.