What Our Gearhead(R) Experts Are Saying:"I've taken the Guardian on expeditions where water quality is genuinely questionable - glacial runoff, river crossings in remote terrain, and international travel - and it has never let me down. The self-cleaning design keeps the flow rate consistent without any extra effort, and knowing it handles viruses puts my mind at ease in a way that a standard microfilter doesn't."Most water filters handle the common threats. The MSR Guardian Purifier System handles all of them. With a 0. 02-micron hollow fiber filter, it eliminates protozoa, bacteria, viruses, and particulate - the full spectrum of waterborne risk - making it the right tool for international travel, high-use water sources, and any situation where the stakes are too high for a standard microfilter. At 2. 5 liters per minute, it moves fast for a purifier, and the self-cleaning design maintains that flow rate in the field without manual intervention. A cartridge replacement indicator takes the guesswork out of filter life, and a rated lifespan of 10,000+ liters means this system will outlast seasons of heavy use without needing a replacement. When clean water is non-negotiable, the Guardian is the answer.