The Namib Desert is on the west coast of Africa and when the morning fog rolls in, the Namib Beetle collects water droplets on its bumpy back, then lets the moisture roll down into its mouth, allowing it to drink.
Devices that collect moisture from fog in similar fashion could collect clean water near homes. A fog-harvesting device consists of a fence-like mesh panel, which attracts droplets, connected to receptacles into which water drips. Interest in fog harvesting dates to the 1990s and increased when new research on Stenocara gracilipes made a splash in 2001. A few technologists saw potential in the concept for people. One Canadian charitable organization, FogQuest, has tested projects in Chile and Guatemala.
Shreerang Chhatre, a doctoral candidate in chemical engineering at MIT, has focused on the wettability of materials, their tendency to either absorb or repel liquids. One basic principle of a good fog-harvesting device is that it must have a combination of surfaces that attract and repel water. For instance, the shell of Stenocara gracilipes has bumps that attract water and troughs that repel it; this way, drops collects on the bumps, then run off through the troughs without being absorbed, so that the water reaches the beetle’s mouth.
To build fog-harvesting devices that work on a human scale, Chhatre says, “The idea is to use the design principles we developed and extend them to this problem.”
To build larger fog harvesters, researchers generally use mesh, rather than a solid surface like a beetle’s shell, because a completely impermeable object creates wind currents that will drag water droplets away from it. In this sense, the beetle’s physiology is an inspiration for human fog harvesting, not a template. “We tried to replicate what the beetle has, but found this kind of open permeable surface is better,” Chhatre says. “The beetle only needs to drink a few micro-liters of water. We want to capture as large a quantity as possible.”
In some field tests, fog harvesters have captured one liter of water (roughly a quart) per one square meter of mesh, per day. Chhatre and his colleagues are conducting laboratory tests to improve the water collection ability of existing meshes.
FogQuest workers say there is more to fog harvesting than technology, however. “You have to get the local community to participate from the beginning,” says Melissa Rosato, who served as project manager for a FogQuest program that has installed 36 mesh nets in the mountaintop village of Tojquia, Guatemala, and supplies water for 150 people. “They’re the ones who are going to be managing and maintaining the equipment.” Because women usually collect water for households, Rosato adds, “If women are not involved, chances of a long-term sustainable project are slim.”
Fog-harvesting technology is not going to be commercially viable. “My consumer has little monetary power,”Chhatre says, but believes the technology could also work on the rural west coast of India, north of Mumbai, where he grew up. But in wealthier countries, schools or businesses might try fog harvesting to reduce the amount of energy needed to obtain water. Still, academics always believe in the power of capitalism when it comes to their research, even though most are taxpayer-funded, and so Chhatre thinks if a sufficient number of collection devices are sold in wealthy countries, it could contribute to a reduction in price, making it more viable in poor countries.
It would just be cheaper to buy them for villages in poor countries.