Fog Provides Water in the World's Driest Zones

Historiansdon't knowexactly how old the practice of fog collection is. Modern engineers have been tinkering with the idea since at least 1901, when fog captureexperimentswere carried out on Table Mountain in South Africa.

The country took a huge leap forward in 1969. That year, South Africa's government was looking to find a suitable source ofwaterfor itsAir Force personnelat the Mariepskop radar station. Two plastic nets — measuring 91.8 feet (28 meters) long by 11.8 feet (3.6 meters) high — wereset up附近的设施。放置在正确的角度other, their purpose was to gather and store windblown moisture on foggy days. The screens stayed up for 15 months. In that time, they yielded a daily average of 11 liters (2.9 gallons) of water per square meter (3.28 square feet) of collection surface area. Not too shabby.

Think of fog banks like grounded clouds. Theproduct of condensation, fog is made up of visible water droplets that congregate in large clusters near Earth's surface. Fog nets — like the ones built for the Mariepskop radar station — are made of fine mesh and typically held up by poles in the ground.

When it's foggy outside, tiny water droplets cling to the mesh. As they accumulate, some of the droplets merge together into beads. When they increase in size, the beadsgrow heavyandgravitypulls them down. At the base of a fog net is a gutter that collects these descending water droplets that can then be diverted into a reservoir for storage.

Ultimately, the Mariepskop nets weredismantledonce a different water source presented itself. But the world hadn't seen the last of fog harvesting. Halfway across the planet, a renaissance in this field was set to unfold.

The Chilean mountain village of Chungungo — like the Namib Desert — is arid and rain ishard to come by. Typically, the area experiences less than 6 centimeters (2.36 inches) of precipitation per year. Generations of residents have had toimportdrinking water by the truckload from Chile's wetter regions. And yet, Chungungo itself is not some moisture-free wasteland. Regular, heavy fogs blow in from the Pacific. So late in the 20th century, scientists decided to try and harness this resource.

In 1992,The New York Times reportedon a collaboration between Chile's National Catholic University and the International Development Research Centre of Canada. Researchers from both organizations descended on a hill overlooking Chungungo where they tested out different net materials. Eventually, the teams settled on a design. Some50 netswere made, with each containing two layers of tight, polypropylene mesh.

Though the harvest yields varied seasonally, a 2001 report from Scientific American found that the nets gathered an average total of11,000 liters(2,905 gallons) of water every day. That was enough to provide each one of Chungungo's 300 residents with 33 liters apiece (8 gallons) daily.

The feel-good story garnered lots of headlines. Inspired by the success at Chungungo, other countries began to set up their own fog-harvesting net systems. Today, these contraptions can be found in more than a dozen nations — including Peru,MoroccoandNepal. In areas where lakes, rivers or water wells aren't options fordrinking water, they can be highly useful.

Fog collection technologycontinues to evolve. In 2013, scientists from the Pontifical Catholic University of Chile and the Massachusetts Institute of Technology announced a vastly improved mesh screen design. Through rigorous testing, they learned that thin fibers made for more effective nets. So, they created a net out of stainless steel filaments with three to four times the thickness of an isolatedhuman hair. Then, a specially made coating was applied in order to help water droplets slide down the mesh more easily. According to the researchers, this new design represents a 500 percentimprovementin fog-collection efficiency.