It’s goes without saying that with more traffic into the backcountry due to the pandemic, it’s more important than ever to filter your water.

Capacity

The MSR Guardian Gravity holds 10 liters of water. This is a significant size for one person but close to perfect for groups of two or more. When I used this, it was on on a two-day backpacking trip on the Sioux-Hustler Trail in the the Boundary Waters of Northern Minnesota. I didn’t find the size or capacity to be overkill for just me. It’s always good to have more than water than you need versus not enough.

Weight

When packed, the MSR Guardian Gravity is a little bigger than the standard 750 ml wine bottle and weighs in at 1lb, 2 ounces. Obviously, this is bigger (and heavier) than my Katadyn Hiker Pro which weighs in at a scant 15 ounces.

To be clear, the Katadyn Hiker Pro and the MSR Guardian Gravity isn’t an apple-to-apple comparison. The Katadyn Hiker Pro is a standard pump-action, labor-intensive water filter. The MSR Guardian Gravity is a self-flowing goliath that frees water of the invisible fluvial zoo of Cryptosporidium, Giardia, E-Coli and Salmonella hands-free.

I didn’t notice the extra weight, especially considering the benefits. Ultra-lighters, however, may feel their knees buckling and spinal discs bulging under the ample weight.

Ease of Use

The MSR Guardian Gravity is a lazy hiker’s dream come true (e.g. me). Gravity, as the name implies, is the key component. This means you will need a tree or some apparatus sturdy enough to hold the filled bag at least six feet above the ground for optimal flow rate. If your backpacking plans include the vast desert or open plains where there are no trees, or you’re spending the majority of your time above treeline, this may not the best filtration system.

Filling the bladder was easy – I just scooped up all the lake water it would hold and rolled the top to closure. Hoisting the full ten liters of water six feet above my head to secure to a tree—not so easy. Impossible, actually.

Filling

After dumping half the water back into the lake, it was manageable. I repeated this process a couple of times as needed at camp. It was all good. Once I secured the bladder to the hang strap tied from a tree, the purge and purification process began without any hitches. Note: The ideal water-to-weight ratio for me to lift is six liters. That’s plenty for me to drink.

Purifying

The MSR Guardian Gravity has two hoses – one short, which is the “purge” hose, and one long, which is the “input” hose. This is the hose that empties into your pot, water bottle or hydration bladder. There is no way to confuse these hoses, by the way. The purge hose is short, black and has a visible “do not drink!” tag.

The very first step to purify your water is to “purge and purify”. To do this, ensure both the purse and input hose clamps are clamped. Unclamp the purge hose first. This flushes the purifier of gunk. MSR recommends you purge about a half-liter of water. I did about a full liter just because. You’ll want to do this every time you fill the bag with new water.

After the ceremonial purge, lock the purge hose clamp and open the inlet hose (the long clear one), and let gravity do the rest. 

Top Tip

Find the right branch first, detach the hang strap and secure it around the said branch. Then fill the bag, carry it to the branch, hoist and secure to the clip. My first time around I was trying to do this all at the same time. A bit of a stupid, bumbling, inefficient way to do it.

Flow Rate

Flow rate is all dependent on how high you can hang the bag. A point of contention here is the length of the inlet hose. I think it could be considerably shorter. If I was seven feet tall and had the strength to lift 100lbs over my head to a tree with a branch seven to eight feet off the ground, I could get the flow rate gushing. But I’m 5’ 6” tall and cannot lift 100lbs over my head so all I got was a consistent, easy trickle. This wasn’t a deal breaker for me but I think MSR should provide the option of shorter hose lengths to accommodate the height and strength of the non-Viking warrior body types.

When timing the flow rate, it was all over the board due to the availability of tree heights and accessibility. On one time trial, I hung the bag the on a tree branch that allowed the bag to hang about four feet off the ground, but with lots of slack in the inlet hose. It filled a 32-ounce Cambelbak Chute in 3:45. Another time trial involved a tree with a branch that I could easily reach, with the bonus of being situated at the precipice of a downward slope. I hung the bag on the low branch and twisted it around to the slope where it hung at least seven or eight feet above the ground. There was no slack in the inlet hose this time. It took 2:12 to fill the Camelbak Chute.   

Water Taste

The water tasted like clean, purified, delicious, refreshing lake water. I tasted no hint of plastic.

Cleaning

The beauty of the MSR Guardian Gravity is that it is self-cleaning. Every time you do the purge and purify process with the purge hose, it’s a cleaning process.

Final Thoughts and a Parting Shot

Is the MSR Guardian Gravity worth the $250 price tag? In my opinion it is. From this day forward, the only reason I would use a hand-pump is if my hike took me to a treeless place. It’s faster and less labor-intensive than my Katadyn Hiker Pro. It’s incredibly well made and reliable. The hose assembly never leaked. The bag is light but incredibly strong with a reinforced bottom to protect it from twigs or rocks should you have to set it down. The filter is designed to last for about 3,000 liters and has a cartridge indicator that tells you when it’s time to change.

The MSR Guardian Gravity is also the only purifier that meets military-grade NSF protocol P248 testing standards. P248 is the most rigorous certification for proving a treatment device removes claimed contamination from challenging wilderness water sources. My only grievance is the long input hose—it could be shorter. Again, hardly a deal breaker.

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