One in three people lives in drylands, areas covering more than 40% of the Earth’s surface that experience significant water shortages.
Scientists and engineers have now developed a new material that could help people living in these areas access clean drinking water by capturing it right out of the atmosphere, according to a new study in Nature Communications.
They’ve developed a gel film that costs just $2 per kilogram to produce and can pull water from the air in even the driest climates; 1kg of it can produce more than 6 litres per day in less than 15% relative humidity (RH), and 13 litres in areas with up to 30% RH.
Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity. So a 100% RH means that the air is completely saturated with water vapour and cannot hold any more. People tend to feel most comfortable between 30% and 50%, and arid climates have less than 30% RH.
These results are promising, as previous attempts to pull water from the desert air have typically been energy-intensive and not very efficient.
“This new work is about practical solutions that people can use to get water in the hottest, driest places on Earth,” says senior author Guihua Yu, professor of Materials Science and Mechanical Engineering at the University of Texas in Austin, US. “This could allow millions of people without consistent access to drinking water to have simple, water-generating devices at home that they can easily operate.”
The gel is made with hydroxypropyl cellulose (HPC) which is produced from cellulose, and a common kitchen ingredient called konjac glucomannan, as well as lithium chloride salt (LiCl). It forms a hydrophilic (water attracting) porous film with a large surface area that collects the water vapour from air.
“The gel takes two minutes to set simply. Then, it just needs to be freeze dried, and it can be peeled off the mould and used immediately after that,” explains Weixin Guan, a doctoral student on Yu’s team and a lead researcher of the work.
And, because the cellulose is thermo-responsive, it becomes hydrophobic (water repelling) when heated which allows the collected water to be released within 10 minutes through mild heating at 60 °C.
This means that the overall energy needed to produce the water is minimised. The film is also flexible, can be moulded into a variety of shapes and sizes, and producing it requires only the gel precursor – which includes all the relevant ingredients poured into a mould.
“This is not something you need an advanced degree to use,” says lead author Youhong “Nancy” Guo, a former doctoral student in Yu’s lab and now a postdoctoral researcher at the Massachusetts Institute of Technology. “It’s straightforward enough that anyone can make it at home if they have the materials.”
And because it’s so simple, the authors say the challenges of scaling the technology up and achieving mass usage are reduced.