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MSR Guardian Gravity Purifier

rated 4.5 of 5 stars
photo: MSR Guardian Gravity Purifier water purifier

The MSR Guardian Gravity Purifier is an all-in-one water treatment system that is ideal for groups, or people needing potable water in larger volumes. Not only removing bacteria, protozoa, sediment and particulate, MSR’s new flagship purifier also removes the tiniest viruses, while also using activated charcoal to improve flavor and reduce chemicals. The Guardian’s new purge valve quickly and easily cleans the filter to maximize flow rate, removing debris.


  • Removes most high risk microorganisms and contaminants
  • Easy to use/Intuitive design
  • Spectacular purge hose system easily cleans purifier
  • Designed well to prevent cross-contamination


  • Price point high, but well justified
  • Weight could be a consideration/subjective rather than a con
  • Like many other filter systems, long-term storage protocol can be daunting


Mountain Safety Research (MSR) is no stranger to water treatment, and even taking a quick look at the Guardian Gravity Purifier, it shows. MSR has been responsibly manufacturing a host of products for over fifty years. You can read more about MSR here.

At the core, MSR Guardian Gravity Purifier is its hollow fiber technology. Unlike all of the other hollow fiber core water treatment products currently available, the pore size filters much smaller particles, effectively removing viruses. This technology came about via the pharmaceutical industry, where specific molecular sizes were required to be filtered for scientific testing. Most competitors filter to the .1 micron rating, whereas the Guardian Gravity purifier has a .02 pore size. This is a milestone in water treatment not only for the recreational field, but also on a global level.

The original MSR Guardian Purifier is still available, for those who prefer a pump style system but want the coverage of MSR's flagship purifier. 


The packability and large volume also make this purifier ideal for international travel, providing important peace of mind for travelers. 

Greatly improved flavor on an upstate New York getaway 



The MSR effectively removes 99.99% of viruses, 99.99% of bacteria, 99.99% of protozoa, as well as sediment and micro plastics. In addition, the purifier system has an activated carbon stage to improve flavor and odor. 


One of the best new features to the MSR Guardian Gravity Purifier is the purge valve/hose. Rather than needing to back-flush, the purge hose quickly dumps the accumulated debris.

For those that have needed to back-flush a filter system regularly, this is an astonishing new way of keeping flow rate at a maximum. 


A quick release clamp can easily be used to open the purge hose (Note: Be sure to purge the purifier away from one’s water station, as to prevent contamination).


 The roll-top style "dirty bag" is easy to fill and seal.



The included storage bag holds all components of the purifier system easily, without being too large or bulky.



Speed & Efficiency

MSR touts a quick .5 liter per minute flow rate for the Guardian Gravity system, which has been shown to be accurate thus far during testing. The system is also very quick and easy to set up. The most difficult task in using this gravity system is lashing the 10 liter "dirty bag" to a height of 6+ feet in order for optimal function.  


This gravity purifier is very easy to use—with added safeguards to help prevent cross contamination, which can easily happen. 

A screw-on cover helps to keep the filtered down-stream cap clean.


The filling cap accepts many different sized caps, from a standard water bottle to a Nalgene bottle, and more.





 The Guardian Gravity Purifier has a 10 liter "dirty bag", which approximates to about 2.5 gallons. This is extremely helpful with groups, allowing everyone in the group to safely refill their containers. Currently, this system is being tested with MSR’s 10 liter Dromedary Bag.


Once the filtered water is collected into the Dromedary, people can easily refill their containers with the easy to use spigot. 

The cartridge has a rated lifespan of 3,000+ liters, which will likely outlast most hikers' lifelong adventures. 


Construction & Durability 

This purifier system is one of the only recreational systems authorized to be used by several national militaries, with an NSF P248 scientific certification. More can be read on this here. The Guardian is engineered to be highly durable, and testing has shown all components to be very high quality. If the filter capsule happens to fall, MSR has a specific integrity test to ensure the system remains safe for use. 



The MSR Guardian is continuing to be tested. Product testing began in mid-spring 2021consisting of several overnight trips in the mid-Atlantic region on the Appalachian Trail.


The MSR Guardian Gravity Purifier is a state-of-the-art purifier for not only backpacking groups, but also travelers that want to ensure safe drinking water on the go. Very few products remove tiny particles down to virus-level (.02 micron), and initial testing shows that this purifier is unparalleled in quality and function. 


I've been using various water filtration and purification methods for over 35 years of backpacking in North America—pump filters, electrolytic purification, UV treatment, gravity filters, tablets etc.

Source: received for testing via the Trailspace Review Corps (sample for testing and review provided by MSR)

About the Author

Sean Van Cleve spends much of his free time as a backcountry guide in the mid-Atlantic USA. A certified Leave No Trace Trainer and Wilderness First Responder, Sean focuses on outdoor education with friends and clients alike. Whether it is recreational high-pointing, section hiking on the Appalachian Trail, or leading multi-day backcountry trips in West Virginia, practicing outdoor ethics is at the forefront of the experience—preserving the land for future generations. 

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Price MSRP: $249.95
Current Retail: $299.95
Historic Range: $249.95-$299.95
Weight 1 lb 3 oz / 0.53 kg
Width 4 in / 10 cm
Length 12 in / 30 cm
Height 4 in / 10 cm
Effective against bacteria Yes
Effective against chemicals/toxins No
Effective against particulate Yes
Effective against protozoa Yes
Effective against viruses Yes
Filter media Advanced Hollow Fiber
Filter pore size 0.02 microns
Flow 0.5 liters per min
Cartridge life 3,000+ liters
Field cleanable Yes
Field maintainable Yes
Water Bottle Adapter Yes
Cartridge replacement indicator Yes
Materials UF Hollow Fiber, ABS
Country of Origin Made in the U.S.A. of U.S. and Imported Materials
Product Details from MSR »

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