Researchers at the SLAC National Laboratory not stop fighting for inexpensive method of purifying water for people who do not have access to drinking water. Recently they created a small device about the size of a postage stamp, which in 20 minutes can purify 25 liters of water contaminated with bacteria, requiring for its operation only sunlight! The device eliminates up to 99.9% of bacteria, but the only downside is bactericidal. Scientists do not give up. They hope to soon expand the scope of operation. Good luck!