A Breakthrough in Fog Harvesting Is Good News for Arid Areas

Systems to harvest water from moisture-rich fog seem like the stuff of the future, but the concept itself is actually quite simple—a variation of water collection techniques used in backcountry and survival situations. Place a plastic mesh vertically in a foggy area, with a collection system at the bottom of it, and when fog descends, water condenses on the mesh and runs down into a collection tank.

The trouble is that these systems aren't particularly efficient. Existing ones only collect about 2 percent of the available water from fog. But a new fog collection systemdeveloped by researchers from MIT radically increases the efficiency of fog harvesting, enabling the extraction of at least 10 percent of the available water contained in the fog.

The researchers did so by decreasing the size of the filaments in the fog-collecting mesh, weaving those filaments into a much finer mesh, and then coating them so that the water runs off much more quickly.

In their tests, the team discovered that the best performance in fog harvesting comes from a mesh made of stainless steel rather than plastic. Each filament is roughly 3-4 times the width of a human hair, and they're woven together so the gaps are about eight times a hair's width.

Testing in the mountains along the edge of the super-dry Atacama Desert in Chile found that at certain times of the year a single of these mesh panels could harvest 12 liters of water a day.

Still, that 12 liters is a drop in the bucket. According to USGS stats on personal water usage, the average person in the US uses roughly 300 liters of water a day. Like most stats on resource consumption, pretty much everywhere else in the world uses less. According to the UN, the minimum water needed daily to meet basic human needs is 20-50 liters.

But that 12 liters is from one small single mesh system. The researchers say that if you placed hundreds of larger meshes in the right place this could add up to some serious water collection.

In fact, researchers calculated that just 4 percent efficient collection of water contained in daily fogs could supply all the water needs of Chile's four northernmost regions. The new systems have a higher calculated efficiency than that, and of course require no energy and occasional cleanings.

The systems will only work outside of survival situations if they can be scaled up—and they need fog, naturally, so they're not a cure-all. It's also unclear how efficiency might be affected if large-scale fog collection begins. Regardless, it's fascinating work.