The worldwide shortage of clean drinking water is a serious problem, although in many cases there’s a relatively simple solution – just leave the tainted water outside in clear plastic bottles, and let the sun’s heat and ultraviolet rays purify it. This approach is known as SODIS (SOlar DISinfection of water in plastic bottles), and it removes 99.9 percent of bacteria and viruses – results similar to those obtained by chlorine. Unfortunately, however, there’s been no reliable way of knowing when the water has reached a safe level of purity. Now, four engineering students from the University of Washington have created a simple, inexpensive device that does just that... and they won US$40,000 in the process.

The UW students took part in a contest promoted by InnoCentive Inc., a company that hosts a website where organizations post technical challenges, and anyone can send in their solutions for a chance to win cash prizes. In this case, the nonprofit GlobalGiving Foundation had asked other nonprofits around the world to submit their water-related challenges, from which it chose five to post on InnoCentive – the Rockerfeller Foundation supplied the prize money. The challenge the students took up had been submitted by the Bolivia-based Fundación SODIS, a nonprofit group that promotes the use of SODIS in Latin America.

The students, Chin Jung Cheng, Charlie Matlack, Penny Huang and Jacqueline Linnes, developed a simple device using parts from a keychain that blinks when exposed to light. When attached to a water bottle, it monitors how much light is passing through the water. An indicator light blinks on and off as long as particulates are still obstructing the light flow, and stops blinking once the water is safe to drink. It is also able to tell when a bottle of water is present in front of it, so it’s not trying to measure data when nothing’s there.

It is estimated that parts for each device would cost about US$3.40, although bulk buying should push that figure even lower. Matlack described it as containing “all the same components that you'd find inside a dirt-cheap solar calculator, except programmed differently.”

Fundación SODIS now holds a non-exclusive license to develop the technology, although a donor from the foundation has offered Matlack US$16,000 to do so himself. Along with Linnes and another student, he is now setting up a nonprofit business called PotaVida to produce and promote the water bottle indicator, and is looking for industry partners to add their expertise.

“We're at a point where we recognize the need for work on this beyond engineering,” he said. “Ultimately, the hardest part is going to be to get people to use it.”