Looking to Nature for Inspiration on how to Draw Water out of Thin Air

Efforts to supply arid regions with water have been undertaken ever since humanity began spreading into the world’s deserts, with ingenious methods being invented throughout history to hydrate populations and their agriculture in deserts and mountains. This problem is becoming more acute as the Earth’s climate shifts: while there are regions that are experiencing increased flooding, there are corresponding locations that suffer more frequent droughts, meaning we need to find new ways of providing the people there with a ready source of water. One engineering team with Ohio State University are now studying new water collection methods, inspired by desert plants and animals, to develop a new generation of simple devices that can literally pull water out of thin air.

Although there isn’t a lot of it, there’s still water to be found in the world’s deserts, it’s just a matter of knowing how to access this precious resource. "We thought: ‘How can we gather water from the ambient air around us?’" explains Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering at Ohio State. "And so, we looked to the things in nature that already do that: the cactus, the beetle, desert grasses."

Along with Ph.D. student Dev Gurera and engineering researcher Dong Song, Bhushan studied the water-collecting structures on these cacti, beetles and grasses to design and manufacture different structures to see how well each shape collects water from the air.
At night, desert grasses and cacti gather condensed water at the tips of their blades and barbs, with the collected fluid guided down the plants by grooves and channels to their roots. Desert beetles have similar abilities, with water-repellant bumps on their backs that allow moisture in the air to condense on them, with the collected water channeled between those same bumps down toward the insect’s mouth.

The research team took these structures and created scaled-up versions using 3D printers, complete with barbs, bumps and channels, and then tested their water-collection abilities in a humidifier-generated foggy environment. They quickly found that cone-shaped structures worked better than cylinders, "which seems obvious in retrospect, because of what we know about grass," according to Bhushan, with grooved surfaces being about twice as efficient at channeling water than smooth surfaces.

The materials that the structures were made of made a difference as well, with hydrophobic surfaces that allowed the water to bead up gathering more water than their more absorbent counterparts. "The beetle’s surface material is heterogeneous, with hydrophilic spots surrounded by hydrophobic regions, which allows water to flow more easily to the beetle’s mouth," Bhushan explained.

Bhushan’s team hopes that their research will result in devices that, when scaled up to industrial levels, can alleviate the scourge of water shortages in affected areas around the world. "Water supply is a critically important issue, especially for people of the most arid parts of the world," Bhushan said. "By using bio-inspired technologies, we can help address the challenge of providing clean water to people around the globe, in as efficient a way as possible."