MSR Guardian Gravity Purifier Offers Epic Viral Protection, 10 Liters at a Time

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.)

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.

Filling the 10L reservoir is a breeze, but what may be trickier is finding a place to hang it. You’ll need to have the bag at least 6 feet off the ground for its optimum flow rate, so pick your site well.

Once your site is sorted, a simple purge of the filter allows you to switch to the 1L-in-2-minutes flow rate of the filter — 2.5 times faster than the competitors, MSR claims. A field test of the Guardian Gravity timed my flow rate at closer to 2:30, but that may be attributed to the hang height or angle.

The clean-water line coming from the filter needs to fill an empty vessel, so if you’re planning to run all 10 L at once, you’ll need a jug or dromedary. Otherwise, use the bottle adapter on the end of the hose to fill one bottle at a time.

The NSF protocol P248 military testing standard requires removal of 99.99% of viruses, 99.9999% of bacteria, 99.9% of protozoa, and sediment and microplastics. Basically, protection from the worst water you may encounter.

In the second step of the process, activated carbon (a component in several other filters on the market) reduces unwanted chemicals, tastes, and odors.

A note on comparison — the Guardian Gravity Purifier is much lighter than MSR's Guardian Purifier pump model ($350), and cheaper too. And it's currently the only backcountry gravity filter on the market to meet military standards.

MSR created the product for the military, so it comes ready for emergency situations and groups. Ideal for a backcountry campsite, the 10L capacity can provide fresh water to multiple folks for an entire day. And it does so quickly.

The easy carrying case and simple setup allow the product to fit in a pack. And the materials make it easy to tote around the backcountry without fear of ripping it to shreds.

This filter is designed to last for 3,000 L, and when the time comes to replace the filter cartridge, you’ll know via the handy cartridge indicator.

This is one of the best purifiers we’ve seen to filter large quantities of water, serving large groups of people. And it removes nearly everything, giving you peace of mind no matter what water source you’re drinking.

At a $250 price point, the Guardian Gravity Purifier won't be for everyone, but it also does exactly what it says it will — a nearly complete clean of any kind of water for a large group. And quickly. With other handheld, single-serve, or pump filters, purifying 10 L could take hours.

While finding the right spot to hang your purifier will be easier in some places than others, that was our only hesitation in the entire process. The Guardian Gravity Purifier simply and speedily cleaned water, even in the sketchiest of situations.

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