The water coming out of my MSR Guardian purifier looked so clean, and smelled fresh, too — it was quite a departure from the pond-scum-like dirtiness I’d dumped in.
MSR’s Guardian Gravity Purifier is designed for backcountry use by the military — and now for anyone enjoying the backcountry because of its 10L size. The purifier meets military-grade NSF protocol P248 testing standards by removing bacteria, protozoa, pathogens, heavy metals, chemicals, and viruses. It does this through a 0.02-micron hollow fiber filter with a carbon component.
We tested a Guardian Gravity in creeks and streams — and in the trees — of the Pacific Northwest, pushing it a little further than expected. (Most people don’t purposefully filter the gnarliest water they can find.)
Looking for a new water filter? Check out how the Guardian Gravity compares to the rest of the market in GearJunkie’s Best Backpacking Water Filters Buyer’s Guide.

MSR Guardian Gravity Purifier Review: Setup
Rolled up like a burrito in a mesh carrying bag, the 1 pound 3 ounce filter, reservoir, and hose is a breeze to set up. The open-top style and malleability of the bag makes it easy to maneuver in a makeshift sink or drag through a stream to fill (my preferred choice).
A simple roll-top design with straps and snaps allows for hanging on a tree. Keep in mind, you need to get this bag 6 feet high for the filter to work properly.
This is sometimes easier said than done, although the included straps help immensely. It is, after all, a gravity filter. The water then flows through a tube into the actual purifier.
From there, the design includes a purge hose that eliminates the need to backflush to clean the filter, and a clean-water hose. We like that MSR made the filter easy to clean in the field.
Both hoses have clips to stop or start the flow of water easily. And, at the end, a bottle adapter hooks to a variety of personal water bottles and jugs.

How the Guardian Gravity Purifier Works

Guardian Gravity Purifier: Who’s It For?
