Is that a piece of bark in your drink? A bug, maybe? Nope. It's a tiny water-purifying tablet powered by the sun.

The device comes from scientists at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University's Institute for Materials and Energy Science. It measures 1 centimeter by 2 centimeters, about the size of half a postage stamp, and decontaminates water fast using a readily available resource -- visible light from the sun's rays.

The invention could let hikers (and later, people living in developing countries) clean their water quickly without resorting to other power-fueled methods, such as the tried-and-true tactic of boiling water, or an ultraviolet wand, which requires charging.

Other devices harness the sun's rays to decontaminate water, but only use UV light, which typically takes anywhere from several hours to two days to work, according to the Swiss Federal Institute of Aquatic Sciences and Technology's Solar Water Disinfection initiative. The Stanford tablet, on the other hand, takes minutes.

Jin Xie/Stanford University

Some 663 million people lack access to clean drinking water, according to the United Nations, and almost 1,000 children a day die from preventable water- and sanitation-related diseases.

"UV light only counts for 4 percent of the total solar energy," Chong Liu, a Stanford postdoctoral researcher and author of a report on the device, said. "If you can also use visible light, that's 50 percent of solar energy, so you just use it for free, why not just use most of the solar to do water disinfection and to harness more light and to use it more efficiently?"

The report appeared in the journal Nature Nanotechnology on Monday.

The little glass tablet is topped with bits of copper and "nanoflakes" of the industrial lubricant molybdenum disulfide, which under the right conditions, produces a chemical reaction that kills microbes.

The tablet boasted some striking early results. In a controlled experiment, it killed 99.999 percent of bacteria after 20 minutes with 25 milliliters of water. It can be physically scaled to treat the necessary amount of water, and it's supposed to cost just a few dollars, according to Liu. The researchers will now test the device in real-world settings and hope it could be commercialized within the next three to five years.

What's the catch? The tablet only works (so far) against E.coli and a lactic acid bacteria, not viruses or harmful chemicals like lead. But the team plans to combat other pollutants in later tests.

"The easiest water we can treat [right now] is in outside activities, when you scoop water from the river and that water is not really cloudy or heavily polluted, but might contain microorganisms," Liu said. "You can dump in the device and it can kill the bacteria."