Diarrhea is the second biggest cause of deaths of children under five years of age worldwide: every year, more than 1.5 million children die because of diarrhea, which often is caused by the consumption of water contaminated with micro-organisms. Purifying (disinfecting) contaminated water therefore becomes a major venue for preventing diarrhea and other waterborne diseases such as cholera or dysentery.
Currently, more than 3 million people in low-income countries worldwide are using solar water disinfection (SODIS) for purifying their drinking water, with the method proven to be simple, low-cost, and appealing to consumers because the water does not change its taste. However, further promotion of solar water disinfection has been slow because the efficiency of the method is not intuitive: no change in the water quality is visible to the consumers.
The Challenge, sponsored by The Rockefeller Foundation, was to overcome this limitation by developing an indicator which gives a visual signal to the user when the process of solar water disinfection has finished – that is, that the water has been exposed to a sufficient dose of sunlight and therefore is safe to drink.