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Freshwater scarcity affects over two billion people in the world, primarily in arid and remote regions, as well as islands and coastal areas without freshwater sources. Climate change and population growth are only making the problem worse, and existing methods require an energy input, usually electrical.

Renewable energy can fix this and is required for these regions for drinking water and irrigation, using water extracted from the atmosphere. (It is estimated the atmosphere holds about 13 trillion tons of water, six times the freshwater in the globe's rivers; global warming allows the air to hold more water vapor, by a theoretical 7% per degree Celsius of warming.)

Now engineers and scientists from Saudi Arabia and China have created a system that uses solar energy to extract as much as 3 liters (0.8 gallons) of water per square meter per day from air, in a purely passive way, requiring no maintenance or human operators. The study is published in the journal Nature Communications.

The system was tested by using its collected water to successfully grow cabbage during two seasons in Thuwal, Saudi Arabia.

"We aim to implement this technology to produce water from the air to compensate the water needs for sustainable agriculture required for secured food production in the Middle East," said Yu Han, a co-author from South China University of Technology.

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