At a time when two-thirds of France's water tables are below seasonal norms, and a quarter of the world's population has no access to drinking water, could collecting fog help combat water shortages? Still little-known in France, this ancient technique has been revived in a number of arid regions, notably in Latin America, where Chile led the way in the 1960s by installing fog-catching nets in the Atacama desert. In Morocco, women from the NGO Dar Si Hmad designed and installed the world's largest operational fog water collection system in 2015, in the mountains of Sidi Ifni, to supply water to several hundred homes.

In recent years, Europe has also seen such initiatives flourish, in Portugal and Spain, where the European Commission has even dedicated a program to them since 2020, co-financed with local authorities. Deployed in northern Portugal and on the Spanish island of Gran Canaria, the European Life Nieblas project has one objective: to reforest some 30 hectares over four years, ravaged in 2019 by violent fires. "Between now and 2024, 20,000 trees are to be replanted on Gran Canaria and 4,300 in the Viseu region of Portugal," said Anne Sarrazin, a technician with the Life Nieblas project in the Canaries. "The special feature is that the forest nurseries are irrigated exclusively with locally harvested fog water."

The basic tool for collecting fog is elementary: movable nets made of plastic (polypropylene) or steel mesh, attached to stainless steel poles 2 to 4 meters high. Positioned facing the wind, which carries clouds and fog, these nets capture the water particles suspended in the air that make up fog. These particles gradually accumulate in the mesh, eventually forming a water net that can be transported or stored. Alain Gioda, a hydrologist at the Institut de Recherche pour le Développement, who took part in fog collection projects in Latin America in the early 1990s, said: "The advantage is that we're not talking about machines, but passive collectors: It's therefore an inexpensive technique, which consumes no energy and presents no risk of breakdown."

"The polypropylene mesh of these nets extracts on average 30% of the water from a fog," said Franck Galland, associate researcher at the Foundation for Strategic Research. Fog water can then be used for everything from irrigating nurseries and farmland to supplying drinking water to remote villages.

But while fog nets can generate significant quantities of water – in the order of 20 to 40 liters per day and per square meter of net – and are economical (with an equipment cost of between 70 and 180 euros for a small collector designed to last 10 years), they remain difficult to generalize on a large scale. "You need wind, clouds and proximity to the sea to be able to collect fog water in significant quantities," said Gioda. Because, without clouds or sea air, fog doesn't form en masse, and, without wind, water particles remain suspended in the air and don't land in the nets. "All the more so as, even in areas with a high fog content, fog is not always present," said Galland.

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