Wired’s outdoor gear team has just completed their most thorough water filter testing for 2026. A reliable water filter is your last line of defense between an enjoyable trip and a distressing one. Think of it this way: a water filter does for backcountry water what a Brita does for tap water, but the stakes are much higher. The MSR Guardian Purifier stands out because it filters viruses in addition to bacteria and protozoa, which most squeeze filters don’t do. By The Numbers: Backpacking Water Filters at a Glance Filter Weight Filters Viruses?