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August 2023

Gear Review: MSR Guardian Gravity Purifier


Guest Authors: Nathan Slater & Sanesh Iyer from @alittlepaddle

When preparing for our 140 day kayak expedition, water management was a big discussion point. Based on the common benchmark of 3L of water per day per person, we figured we'd carry about 3 days of water at any given time (18L for two of us). Our preferred method of doing this is with two 10L MSR Dromedary water bags, stored between our legs in the cockpit of our kayak. This is the best place to store water in a kayak, as in case of a leak you don't end up with water in your sealed, dry, hatches. We typically remove the 10L (10kg) Dromedaries and our Guide bags (~5kg) to lighten our boats, prior to lifting and carrying them.

Alas, the inevitable conundrum is how do we refill our Dromedaries with purified water after 3 days. There are a few options, including chemical purification, UV sterilization, boiling, and filtration. Chemicals work well and fast, but don't taste good and typically cause me to get an upset stomach after a couple days of use. The UV sterilizers use electricity, not something we have an abundance of in the backcountry. Boiling works well, but uses fuel which adds weight and bulk. This leaves filtration, which uses a porous (full of holes) materials and pressure to purify the water.

There are a few different contaminants in backcountry water.

The first is suspended solids that make the water opaque -- like dirt, glacial flower, sea weed, etc. All water purification techniques are best done with clear water, free of suspended solids. You can remove these with a pre-filter (like a mesh cloth) or the use of special chemicals (floculants). Or even better, find water sources with clear water.

The second are biologicals, protozoa, bacteria, and viruses. These are easily removed by UV and chemicals. Most filters can only eliminate bacterial risks. The MSR Guardian series is unique in its ability to remove protozoa, viruses, and bacteria using filtration.

And third are all the things that you effectively cannot deal with, such as toxins (i.e. lead) & dissolved substances (i.e. salt). The only practical way to manage this category of contaminants is to make sure to drink only fresh water from running sources, away from places (mines, industrial sites, etc.) known to leach toxins into the water.

All that to say, if you want clean water in the backcountry for an extended period, you have effectively one option, an MSR Guardian Purifier. We chose to go with the Guardian Gravity because it is easy to use (so long as you have a place to hang it, more on that in a bit). It takes up about the same amount as one MSR 1L fuel bottle, but can filter much more water than can be boiled. And it's the only filtration type purifier that is rated to remove protozoa, bacteria, and viruses, according to NSF P231 & P248 standards.

The Guardian Gravity Purifier can be screwed on directly to a Dromedary or Nalgene bottle, allowing them to be filled directly. The filter ships with a "Dirty Water" roll top bag -- for easy & fast filling -- made of the same materials as the MSR Dromlite line.

Over the last 100 days, we found the Guardian Gravity Purifier spectacularly easy to use. We found it purified fastest when hung 10ft up and the lines are free from bubbles, as recommended by MSR. It also worked in many situations when hung as low as 5ft off the ground when height was limited. The best part of this purifier is once it's setup, you can leave it alone. There's no pumping or anything else to do. If I was somewhere where it was harder to hang the water bag, the classic pump version of the MSR Guardian Purifier would be my preference.

After every 10L of water, we cleaned it by sealing off the outlet line and opening up the purge valve line. If the water was particularly dirty we did this more often. When you open the purge valve line you will see the contamination that the purifier has removed from your drinking water. Purging until the water runs clear, you then seal this line and reopen the fill line. This takes seconds.

This semi-autonomy was very useful with large groups -- for 2 weeks 7 of us paddled together -- as it allowed me to quickly filter water while also cooking dinner or socializing.

We've also found the purifier to be durable. We're careful with it, for sure. It's stored in a safe place in the kayaks and handled carefully. But it's still been out here for over 100 days.

There are a few small things I'd improve. I'd prefer if the Dirty Water Bag was made of the classic Dromedary material for increased durability. I'd also prefer if there was a way to seal the Dirty Water Bag, so you could more easily carry dirty water from source to camp. And it would be nice if the storage bag was a semi-rigid hardshell (like a glasses case), rather than a soft bag, to protect this piece of critical kit.

But the most important thing:

We haven't gotten sick. I have no way of telling you if the Guardian Gravity Purifier saved my life or not. But it's easy to use, takes up minimal space, and is durable when handled as you would any piece of life-supporting-backcountry-gear. There are smaller options, but none that filter viruses. It's a piece of kit I'll keep using for many more expeditions.