A better fog-trap

EVERY NIGHT, air cooled and moistened by the Humboldt current blows over Chile’s northern coast and across the Atacama desert. The billowing banks of fog thus created might look insubstantial, but there is water here to be captured—and in this, the driest place on Earth, . Fog-harvesting will never be big business, for it needs particular conditions to operate well. But in zones like the Atacama, where moisture-laden breezes bring fog but no rain, the invention in the 1960s of traps which can pluck that moisture from the air has helped sustain settlements otherwise on the brink of drought.Fog traps are polymer-mesh screens mounted in metal frames (see picture). As misty zephyrs blow through them, droplets of water adhere to the mesh. These absorb others until the result breaks free and runs down the screen, as a raindrop runs down a window pane, into a collector. A typical trap, with a 40-square-metre collecting area, yields about 200 litres a day. That is enough to supply around 60 people with drinking water. Such a collector costs $1,000 or so, and will last a decade.