The MSR Guardian Water Purifier turns mud puddles into clean, safe drinking water. Literally. With military-grade engineering and game-changing technology, the Guardian Purifier is simply the safest, easiest way to purify water virtually anywhere on earth. It's easy to use. It's totally portable and packable. It's built to withstand harsh conditions. It cleans itself. And it works. Every time. What makes the Guardian so effective? Game-changing Hollow Fiber Technology. Unlike most other water filters on the market, the Guardian actually protects against viruses, the tiniest waterborne microbiological threats. How? The world-renowned MSR water research lab spent six years of extensive R & D, engineering and funding developing state-of-the-art medical-grade Hollow Fiber Technology that blocks viruses, plus removes bacteria, protozoa and particulates. And the revolutionary fibers can't be damaged by freezing or impact. Easy to use. Plusa |it cleans itself! The Guardian filters directly into your water bottle, which means no annoying extra hoses. Plus, on every stroke, the purifier uses 10% of its water to flush remaining filter contaminants back into the source water. This means you'll never hassle with back-flushing or scrubbing cartridges to maintain its fast flow. And the flow is, well, FAST. It purifies up to 2.5 liters per minute. Plus, it's built to last the long haul, treating up to 10,000 liters. So no matter how far you venture, how high you climb or how long a natural disaster contaminates your drinking water, the Guardian will be ready for action. In one easy step, it removes: viruses, including norovirus/norwalk, rotavirus and hepatitis A; bacteria, including E. coli, shigella, salmonella, and cholera; protozoa, including giardia, cryptosporidium and amoebae; particulates, including sediment, silt and dirt Does not require chemicals, prefiltering, bulbs or batteries Meets U.S. Military testing