The Steripen Ultralight is the smallest portable UV water purifier available. It's best for individual use during emergencies and international travel. Treat up to 20 liters of water on a single charge from its high quality USB rechargeable battery which holds charge for months so it is ready when you need it. Ultraviolet (UV-C) light rays safely purify clear water by destroying 99.9% of protozoa (including Giardia and Cryptosporidia), bacteria and even viruses.