Steripen UltraLight UV water purifier is the smallest and lightest at 76 grams. It treats 1 liter of water per use. Running on a searchable USB battery that lasts several months, it can purify 20 liters of water between charges. The life of the UV lamp is 8000 liters. The ultraviolet rays of the lamp purify clear water by destroying 99.9% of protozoa (including Gardia and Cryptosporidium), bacteria and viruses.