BBC: All air, from arid deserts to humid cities, contains water vapour – globally, an estimated 3,100 cubic miles (12,900 cubic kilometres) of water is suspended as humidity in the air around us. That’s more than all the water in Lake Superior, the largest lake in North America (11,600 cubic km), or five Lake Victoria’s (Africa’s great lake, at 2,700 cubic km). Or a whopping 418 times the volume of Loch Ness.
But we’re not talking about clouds. This is the humidity in the air we breathe, that reappears as beads of water on the side of a cold drink, or as morning dew on blades of grass. And a technological race is underway to harvest it as drinking water. If the emerging ‘water from air’ (WFA) devices can crack it, it could go a long way towards solving the world’s freshwater problem.
By 2025, two-thirds of the world’s (rapidly growing) population are projected to be living in conditions of severe water stress. Already, 2.1 billion people live without clean drinking water. The world’s poorest are being overcharged for water they know to be unsafe, but have no other option but to drink. Contaminated drinking water causes half a million deaths from diarrhoea each year. While in richer countries – which consume more water than poorer nations, due to intensive agriculture and industry – water from underground aquafers and river basins are being depleted faster than they are being replenished. On top of that, there is also a trust issue, as citizens doubt the quality of water the authorities tell them is safe. In the city of Flint, Michigan, tap water has been found to include radioactive materials, arsenic and lead. Middle class consumers are turning to bottled water instead. The global bottled water market has grown by 10% every year since 2013, reaching 391 billion litres sold in 2017 (that’s more than 150,000 Olympic-sized swimming pools).
A viable, off-grid source of freshwater is both desperately needed to reduce sickness and poverty, and highly attractive to richer consumers, too.
Pulling water from thin air is hardly a novel concept – you may have a dehumidifier machine at home that does just that. But the water it captures is not clean, doesn’t contain the minerals we need, and the energy required is not realistic to meet a household’s water requirements, let alone a community’s.
There are several companies, however, adapting dehumidifier technology for drinking water. Mechanical dehumidifiers contain chilled metal coils filled with a refrigerant gas, much like a kitchen fridge-freezer, which create an artificial ‘dew-point’ (the temperature at which water vapour in the air saturates, turning from a gas into a liquid, like the beads on the side of your ice-cold drink). Water vapour entering a WFA machine condenses on a chilled coil in the same way, but once collected it is filtered, sterilised by UV light, mineralised, and stored in a food-grade tank ready to drink.
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