Sawyer Two-Bag Complete Water Purifier System Two-bag gravity water filtration system with 0.02 micron absolute filter for backcountry camping and emergency preparedness Goes one step beyond Sawyer MINI and and Squeeze Filter to remove 99.997% of viruses (plus 99.99999% of bacteria and 99.9999% of protozoa/cysts) Housing material made from food grade ABS plastic is easily field maintainable; includes faucet adapter for a more thorough backwash when you get back home Easily create bag-to-bag gravity system with two 4-liter bags (grey marked DIRTY, blue marked CLEAN); purifies up to 4 liters of water in about 10 minutes Backed by manufacturer's lifetime limited warranty