In Chile, world's driest desert slakes thirst with fog

ALTO PATACHE, CHILE: Every morning at dawn, a thick mist known as "The Darkness" blows in from the Pacific to the edge of the Atacama Desert, the most arid place in the world.

After tantalising the northern Chilean desert with the promise of moisture, the mist evaporates in the sun, leaving the heat to bake the stark lunar landscape.

But the South American country is researching how to use a technique called "fog harvesting" to collect this mist in large quantities and deliver it to communities that currently depend on water shipped in from the city in tanker trucks.



Chilean researchers have patented a device resembling a large window screen to turn the mist into usable water.

These fog harvesters are set up facing the wind, which blows the mist into myriad tiny black threads that criss-cross them.

Instead of passing through, the mist condenses on the polypropylene threads, slowly gathering into drops that eventually seep down into an awaiting container.

The technique is basic but efficient: each window-sized device can collect 14 liters (3.7 gallons) of water a day, said Camilo Del Rio, a researcher at the geography institute of Catholic University in Santiago.

The university runs a research center on fog harvesting in the northern city of Alto Patache.

The technology has been exported to Spain, Nepal, Namibia and several other Latin American nations. Other countries collect water with the same principle, but using trees to gather the condensed moisture.



The water tastes like rain, but must be treated for drinking because it contains minerals from the ocean and can harbor bacteria.

"Transforming it into potable water isn't complicated or expensive," and it can be used as is for bathing or irrigation, said Del Rio.

The research center in Alto Patache comprises six white domes with a weather station, a kitchen, bedrooms and bathrooms -- all of which run completely on harvested fog, which provides the facility with more than 200 liters of water a day on average.

The first fog harvester was installed in the desert in 1992. Around 150 have been deployed since then, though only 40 or so are currently in operation.

The Atacama Desert's dawn mist is produced by the intense solar radiation that hits the nearby Pacific, evaporating large volumes of water that is then carried inland by the region's strong winds.

When this moist air mass reaches the snowy peaks of the Andes mountains west of the desert, it cools and turns to a thick mist.

The indigenous people native to the region call the mist "Camanchaca," which means "The Darkness" in the Aymara language.

Using it for water is an old idea.

The Aymara have long collected condensed mist as it dripped from the rocks.

Today, researchers say, fog harvesting could enable entire communities in Chile's parched northern reaches to be self-sufficient for water, despite the near-total absence of rain.

"This mist is a blessing," said Del Rio.

"We live in an extremely arid, desert climate... but we have this moisture from the ocean."

The lone drawback? Inconsistency. The amount of water collected by a single fog harvester can range from 14 liters a day or more in winter to zero in the summertime.



The average is around seven liters a day across the year.

Researchers are looking for ways to store the water and make the supply more predictable for residents.

"The challenge in studying the mist is to find ways to transport it and bring it to the communities," said Nicolas Zanetta, who runs the research center.

"There are small villages that have no potable water and have to constantly be supplied by tanker trucks from the city... In the future, the idea is to try to implement systems like this across the region."

Chile has already made a start.

In the Coquimbo region, 2,000 residents rely on fog harvesting for their water supply and there is even a local beer made with condensed droplets of mist.