A small, solar-powered device that pulls fresh water from the air? Scientists at MIT and UC Berkeley have created a prototype that does just that -- and it only requires 20-30 percent humidity to work.

Professor Omar Yaghi, one of the senior scientists on the project, is calling the harvester "personalized water." He envisions a future where water is supplied "off-grid, where you have a device at home running on ambient solar for delivering water that satisfies the needs of a household," Yaghi said in a release.

Yaghi, a UC Berkeley chemistry professor, is also the inventor of the key element of the water harvester -- metal-organic frameworks, or MOF. MOFs are compounds created by combining metals with organic molecules. The resulting materials can be highly absorbent, making them ideal for storing liquids and gas. There are now some 20,000 different MOFs created by researchers and scientists with different properties and applications.

In this case, Yaghi and his team at Berkeley created a MOF that binds to water. He then approached mechanical engineer Evelyn Wang of MIT about using the MOF to create a water-collecting device.

The harvester created by Wang and her students was able to produce 3 quarts (2.8 liters) of water using 2.2 pounds (just under a kilogram) of MOF over a 12-hour period. It's a passive device, requiring no other energy source than the sun -- and doesn't even need very bright sunlight to function.

This, in addition to its ability to operate in low humidity conditions (generally below 40 percent humidity is considered dry air), means the harvester could represent a huge breakthrough for bringing water to places that desperately need it. Both Yaghi and Wang believe they've barely tapped the concept's potential. For example, the current MOF can absorb 20 percent of its weight in water. Future MOFs might be able to absorb 40 percent or more.

Freshwater scarcity is a global problem of immense proportions. Recent estimates show 4 billion people -- that's two-thirds of the world's population -- experience acute water scarcity at least one month of the year. Half a billion people don't have enough water all year round.

This crisis extends far beyond the developing world. California's historically severe drought has finally just ended, but the state typically experiences big fluctuations in rainfall from year to year. Climate change could make those swings even more extreme (check out this cool Gizmodo gallery showing differences between California in drought and California today).

Maybe in the not-too-distant future, we'll all have one of these devices to tide us over till the rains come again.

Batteries Not Included: The CNET team reminds us why tech is cool.

CNET Magazine: Check out a sample of the stories in CNET's newsstand edition.