MSR Guardian Purifier Review

The MSR Guardian is a water purifier, rather than a standard filter. This means it goes one step further than your average filter by physically removing protozoa and bacteria and destroying viruses. It is a reliable hand pump filter that also has the advantage of being easier to use in shallow and turbid water. The durable polyurethane housing protects the freeze-tolerant hollow fiber filters from damage and drops (up to 6 feet), while the fast and consistent flow rate can produce around two liters per minute. So long as you don't mind the extra weight and bulk of the filter, it's perfect for anyone seeking a dependable filter no matter the source.

Water Quality

All of the models in our review filter out contaminants like protozoa (Giardia and Cryptosporidium) and bacteria (E. coli and Salmonella), but the MSR Guardian takes it a step further and also completely purifies your water by removing harmful viruses. It does so through its medical-grade 0.02-micron pore size, which is much smaller than the typical 0.1 or 0.2 micron pore size. Controlled lab tests done by a third party, SGS labs, showed that the Purifier was among the top performers, removing >99.9% of each contaminant tested.

While viruses are less of a concern when hiking within the U.S., they more common in countries with less developed sanitation systems, which makes the Guardian a good choice to bring along when traveling through the backcountry in international destinations.

The only downside to this incredible filter is that it does not include activated carbon; it isn't capable of removing chemicals, heavy metals, or odors. That said, we filtered from some pretty dank water sources and mineral-rich streams without detecting any strong flavors or odors in the purified water we drank. In fact, the Purifier is the only filter of the entire lineup that can maintain performance in turbid streams, making it a great choice for spring ski traverses or international travel when you're filtering for a small group.

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Ease of Use

It doesn't get much easier than the Guardian setup. The hand pump filter ships ready to use; simply remove the packaging, attach the beefy hose to the filter, place the hose into the water source, and start pumping. Our right-handed testers appreciated the design of this filter, as the way the hose attaches offers the best ergonomics for those who are right-handed. Thanks to the long hose, this type of filter is also perfect for shallow water sources, small puddles, and hard-to-reach locations, say under a large tree branch or in between boulders. The hose features a mini-filter attachment that successfully sifts through larger debris and particulates, eliminating any resistance with the hand pump and allowing you to purify your water with relative ease.

While the Guardian is not complicated to use or set up, there's no doubt that the process can be long and tedious. It requires you to sit in the same location while you earn your hydration by manually pumping until your bottle is ful. It also requires a separate water vessel to pump the water into, which can eat up space inside your pack. We also noticed that the pre-filter on the hose is worth mentioning, as it can slow the flow rate if it's not oriented correctly. Overall, the Guardian is perfect for difficult to reach locations, shallow, and particularly murky or mineral rich water sources thanks to its user-friendly design and relative ease with every pump.

Durability and Maintenance

The extra weight and bulk of the Guardian Purifier may be off-putting for ultralight aficionados, but the durable polyurethane housing, the long-lasting filter life (up to 10,000 liters), the convenient carry case, and extra-large hand pump might be a worthy exchange for the average hiker.

That said, we did experience a durability issue during our most recent round of testing: the filter's piston nut broke after minimal use. We were easily able to warranty the part with help from the Cascade Designs support team, allowing us to repair the filter and continue testing after about a two-week turnaround. We can't speak to the construction quality of every Guardian filter out there; ours may have been a fluke. However, we're not sure what we would have done had the filter stopped working deep in the backcountry. Just a reminder to always double-check your gear is in working order before heading out, and always bring a backup filtration option, like purification tablets or a filter straw.

In terms of maintenance, we love that the Guardian self-cleans with every pump, requiring little maintenance over the life of the filter. MSR states that with every pump, the filter uses a portion of the incoming water to flush the filter, keeping it clear of debris and maintaining a consistent flow rate, even in the murkiest water sources. That said, we highly recommend letting your filter fully dry between uses, especially before storage. Despite a minor durability issue during our most recent round of testing, we still think this filter offers bomber construction that's built to last.

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Treatment Time

On average, the Guardian successfully filtered and purified water at a flow rate of up to two liters per minute. This is among the fastest filtration times across the board, but is especially good for a hand pump filter. Perhaps we weren't fully “giving it the beans,” but we were never able to achieve the advertised flow rate of 2.5 liters per minute despite a fresh filter in relatively clear water sources.

Unlike other hand pump and hollow fiber filters that we've tested, the Guardian's flow rate doesn't slow down in thick and murky water sources, making it a great choice when you're drawing water from less than ideal sources. An efficient flow rate is essential, especially when you're doing all the work. We think you'll appreciate the fast treatment time whether pumping in clean or turbid water sources.

Weight and Packability

Overall weight, bulk, and packability isn't exactly where the Guardian shines. In fact, weighing in at 20.5 ounces for the entire kit and storage bag, it is the heaviest water filter in our review.

When it comes to overall volume, the large pump, beefy hose, flotation device on the hose, and thick plastic casing also require extra space inside your backpack. That said, the carry case is excellent for keeping all the parts contained, and the filter packs down to roughly the size of a Nalgene bottle. Still, the Guardian is certainly overkill for most backcountry users; it is a niche and reliable design that is worth the extra weight and volume for special cases, like international travel or trips that take you to mineral-rich or murky water sources.

Should You Buy the MSR Guardian Purifier?

The MSR Guardian Purifier is a worthy choice for anyone seeking a reliable filter to handle the worst water conditions.

We love this hand pump filter for its ease of filtration, self-maintenance, and flow rate efficiency even in the murkiest water sources. Along with removing bacteria and protozoa, it can even filter out microscopic viruses, which is a great consideration if you plan to travel outside the United States. The exceptional filter lifespan, durable components, and freeze-tolerant fibers will allow for a long return on your investment. So long as you're not overly concerned about the extra weight and bulk of the Guardian, it could be the perfect way to maintain hydration during your next international trip. That said, not everyone deals with the types of conditions this filter is meant to handle, and it may be overkill for the average hiker. The higher weight, larger size, and not to mention the hefty price tag, may all be reason enough to look for a different filter for more typical backpacking trips.

What Other Backpacking Water Filters Should You Consider?

The Grayl Geopress is another great option for those seeking water purification for international trips. This bottle-style filter is similar in weight and volume, but is more affordable and can be utilized with drink mixes and electrolyte tablets without damaging the filter cartridge.

If Guardian is truly overkill for your next North American adventure, we love the LifeStraw Peak Squeeze, which is a collapsible soft bottle design that features a durable, quality design that's perfect for personal use. If you'd rather stick with a pump filter but would rather purchase a more affordable option, the Katadyn Hiker Pro is worth checking out, especially since it's a fraction of the cost.