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The solar water disinfection method, or SODIS, sounds little too good to be true: simply fill clean plastic bottles with water, then leave them in the sunlight for six to twelve hours and the UV-A rays will kill viruses, bacteria and parasites. The problem, however, is how to ensure the purification process is complete, and this uncertainty has greatly affected the adoption of the SODIS method worldwide. That’s where PotaVida comes in. PotaVida isn’t a water purification system, but rather it’s a way of checking when water has become pure after being subjected to the SODIS method. Created by University of Washington engineering students, the design has received prize money of USD 40,000 after winning the InnoCentive Inc. international competition. Having originally experimented with chemical test strips, the final PotaVida system actually uses an electronic sensor to detect the water’s purity. One of the specifications for the competition was that entries should cost no more than USD 10 to produce. The students calculate that the parts for their design retail at USD 3.40, with bulk buying possibly reducing this even further. PotaVida may have confronted the primary challenge of the SODIS method, but the students will now have to persuade charities and non-profit organizations that their solution is a cost-effective way to save lives. (Related: Water bottle’s plunger-style filter purifies instantly — Water bottle with integrated filter purifies as you drink.)