How to harvest moisture from the atmosphere

Even in the most speculative reaches of science fiction, there is no escaping humanity’s dependence on liquid water. Luke Skywalker, the hero of the original “Star Wars” trilogy, grows up on his uncle’s moisture farm, extracting water from Tatooine’s arid atmosphere. The residents of the desert world Arrakis, accessible to anyone with a copy of Frank Herbert’s novel “Dune” (or with three hours to kill at their nearest cinema), likewise use windtraps to steal precious liquid from the air.

Engineers on Earth, too, are increasingly looking to the atmosphere for water. They have good reason to do so. Even in the depths of Chile’s Atacama Desert, often called the driest place on Earth, estimates suggest that fog and dew can generate some 200ml of water per square metre. Elsewhere, the atmosphere is even more generous. Worldwide, it is estimated to contain 12,900 cubic kilometres of water, roughly the volume of Lake Superior. Moreover, models indicate that evaporation driven by global warming will increase these levels by 27% over the course of the next 50 years.