Americans take tap water for granted. We tend to assume we can have all the potable water we want with the twist of a tap. But with rising temperatures and population growth depleting freshwater sources faster than they're being replenished, experts say we may no longer be able to depend upon a seemingly endless stream of water piped in from reservoirs. Compounding that problem is the looming failure of the nation's outdated water mains — a problem some wags call "pipeageddon."
Now researchers across the country are working on a solution. They're developing low-cost, high-tech devices that can suck drinking water straight from the air.
One of the nascent technologies, under development at the University of Texas, is called an atmospheric water generator, or AWG. It uses a special refrigerator to condense water vapor from the air, filtering it, and then depositing it into a collector for use. It's best suited for humid climates.
Another approach, being developed at MIT and the University of California, Berkeley, uses special crystals that soak up atmospheric water vapor like a sponge. This so-called "water harvester" seems to work in arid as well as humid climates.
These twin technologies aim to exploit the fact that Earth's atmosphere contains not just air but nearly 13 trillion liters of fresh water. That number stays fairly constant, with rain bringing moisture to the planet's surface and evaporation, mostly from the ocean, returning water to the air.
Automatic water generator
In prototype form, the AWG being developed at Texas is the size of a desktop printer. But within the next five years, the researchers hope to commercialize AWGs about a meter high and wide that would be installed in yards and on rooftops. They think it might sell for about $100.
If the scientists' vision pans out, some homes won't need a well or connections to a municipal water system. And the water collected by an AWG will have fewer impurities and dissolved minerals than tap water. As Dr. Vaibhav Bahadur a professor of mechanical engineering at UT and the leader of the research, puts it, "Water that has been condensed from the air is pure, pristine water."
In a suitably humid climate — like that in Texas and California — an AWG should be able to collect about 23 liters of water a day. That's well above the 13 liters a day typically consumed by a family of four.
Bahadur acknowledges that AWGs probably won't make sense for arid climates. But he has high hopes for the technology.
"Our vision going forwards is for every home in America to have an atmospheric water generator," he says. "Realistically, this probably won't entirely replace piped water, but in many cities, it could provide a substantial fraction of people's water requirements each day."
The atmospheric water harvester under development at Berkeley consists primarily of a thin copper sheet coated with water-adsorbing crystals known as metal organic frameworks.
"To the human eye the crystals look like a powder," says Dr. Evelyn Wang, a professor of mechanical engineering at Berkeley and one of the water harvester's designers. "But each crystal contains these tiny pores, of the order of nanometers, which collect the water molecules."
In prototype form, the water harvester is powered entirely using heat from the sun. At night, it soaks up water. When the sun comes up, a solar reflector directs sunlight onto the crystals, causing them to release their water in vapor form that is then directed onto a metal condenser plate. The droplets that form trickle down into a collector.
The researchers say their prototype harvester, no more than a foot tall and half a foot wide, can collect about 3 liters of water a day. Larger harvesters could generate far more water — enough for a family — if powered by electricity. But keeping the device economically attractive becomes a challenge.
The energy challenge
Finding an economical source of energy, sufficient to generate large quantities of water, is one of the main challenges facing the researchers developing both technologies.
An AWG should produce drinking water at a cost of 5 cents a liter. That's cheaper than bottled water but far costlier than tap water, which can be had for a tiny fraction of a cent per liter. Electrically powered water harvesters could be even pricier.
Bahadur thinks landfills may provide a solution — in the form of methane generated by rotting organic waste. This could be used to power turbines that generate low-cost electricity that can be transmitted to homes in the area and used to power AWGs or water harvesters.
In Dallas alone, Bahadur says, "we've calculated that using this waste energy could generate 100,000 gallons of water directly from the air… Perhaps one day, every home in America could generate all their water needs from the air."