Back to top

Please select a color/color.


  • Winner of both Backpacker Magazine's 2016 Editors' Choice Award and Outside Magazine's 2016 Gear of the Show Award
  • Unlike conventional hollow-fiber technology, the advanced medical-grade fibers in the Guardian block viruses—something most other hollow-fiber filters cannot do
  • Physically removes viruses, bacteria, protozoa and particulate, including hepatitis A, E. coli, giardia, cryptosporidium and more
  • Purifies 2.5 liters per min.
  • With every stroke, the purifier uses 10% of its water to flush the contaminants in its filter back into the source; this means you'll never have to hassle with back-flushing
  • Rugged construction is designed to withstand freezing and drops up to 6 ft.

Made in USA.

View all MSR Pump Water Purifiers

REI membership


Best Use Camping, Travel
Filter Type Pump
Filter Medium Advanced hollow fibers
Removes/Destroys Protozoa, Bacteria, and Viruses
Pump Force 4 pounds
Pump Strokes Per Liter 35
Output 2.5 liters per minute
Housing Material Polyurethane
BPA Free Yes
Field Cleanable Yes
Dimensions 8.2 x 4.7 x 3.5 inches
Weight 1 lb. 1.3 oz.
Rated 5 out of 5 by from Essential Item I used the MSR Guardian on my recent 11 Day trek at Philmont Scout Ranch in New Mexico. Its performance was nothing but flawless, except when I over tightened a Nalgene Bottle onto the bottom fitting where it screws into. This caused the Guardian to leak water along the fitting when pumping rather than through the water outlet. To fix this self inflicted problem, I had to loosen the fitting, which allowed the Guardian to work properly again. Other than that, the Guardian served our crew of 10 very well. It pumps fast and easy and it filters out everything to include viruses. I highly recommend that Boy Scout Crews consider taking a couple of MSR Guardians on a Philmont Trek!
Date published: 2016-06-24
Rated 5 out of 5 by from Best in breed, my "go to" backcountry purifier! PERFECT backcountry pump. Rugged, unbelievable throughput volume of water. Easy to use. Solid construction. Convenient storage bag included. fine mesh pre-filter keeps most of the "muck" out of the filter and the backwash system works great to keep the filters clean. Yes, over $300 is allot of money, but I have spent that, and more, on the six Katadyn Hiker Pro models that I have had to purchase for various reasons (breakage, malfunctioning, clogged filters, back-ups, etc.) that process water at 1/3 the rate. Great product that I highly recommend if you can afford it.
Date published: 2016-03-01
Rated 5 out of 5 by from Great replacement for MSR Miniworks I've used a Miniworks for years, but wanted something that would do a better job at cleaning the sketchy sources of water in the mine areas of PA. I've had this for a couple of weeks now and I love how fast it is and how it backflushes itself in order to maintain the filter clean. I have yet to experience a slow down. I've tried it in several sources of water from clear running streams to muck filled puddles, and this filter cleans them all without clogging. On the puddle that I tried, I would have had to scrub the miniworks filter multiple times to complete one liter of water. It is a bit bulky, but worth it considering the filtering and self maintenance that it does. The one star reviewer isn't reviewing this product as it was just released to the public in 2016. He couldn't have tried a "2012 version," so you shouldn't lend any weight to their review.
Date published: 2016-03-25
Rated 5 out of 5 by from Why is this no longer available? No idea why REI stopped selling this product so quickly. This thing works great. The flow rate is quick, there is basically no maintenance involved, and its a one stop shop for water, no need for a filter and purifier because this does it all in one step. Filter is rated for 10,000 liters of water, which to me makes the price point worth it. I don't have to carry batteries for a UV source and I don't have to buy tablets and wait for those to do their thing.
Date published: 2016-06-02
Rated 5 out of 5 by from ULTIMATE PURIFIER ! Took it to my favorite spot up in the mountains and purified water that was brown from rain drainage coming off the mountain , tasted great and no grit , the next test I put it through was to purify the water that was in my green un cleaned swimming pool , tasted great
Date published: 2016-02-02
Rated 5 out of 5 by from Guardian Filter I purchased this product a few months ago and it has performed just as advertised. We did a six day trek on the PCT last month finishing with The Whitney Summit. The three of us relied solely on the Guardian for our water purification. The speed and ease of use was great. We also own a couple of other MSR filters, but they have been stored away for back up. No drops just clean fresh tasting water. Since our PCT trek, we have hoofed it into some areas with not the greatest selection of running creeks, I would say a couple of times we pulled from stagnant pools, but still the Guardian performed.
Date published: 2016-08-15
Rated 5 out of 5 by from Amazing water purifier for backpacking The other one star review on this is for a different product. If you are looking for a backpacking purifier (this does a better job than a typical filter) then this is it. The only drawback with this device is the weight. At about 16 ounces it is a bit heavy. However considering you will have far more options for collecting water I think it balances out. I was using the Sawyer Mini, but I've heard of other backpackers picking up viruses and some even dealing with the fall out for years after. I simply don't trust the water sources enough to rely only on a filter that doesn't catch any of the really tiny stuff like viruses. This purifier will give you a lot of peace of mind. I was hauling both a Steri pen and a Sawyer mini, but this is a far better option. Functionally it works amazingly well. Since it back flushes while you are collecting water there is no cleaning or maintenance to worry about. The flow rate is very fast especially considering the level at which it is purifying the water. It's about the size of a water bottle and comes with a nice carrying case, although I didn't want the weight so ditched that. I found that there are vents at the bottom of the device. So be aware that when you do the integrity test water will leak out. This is totally normal. You don't want to tighten the ring, it can actually block it from working properly causing water to spray out around the ring instead of through the outlet port.
Date published: 2016-03-22
Rated 5 out of 5 by from Beyond Excited I think the other review is a mistake, as the user is mentioning "cleaning the ceramic filter", as well as buying the product in 2015 (The Guardian is new for 2016). I have yet to put my Guardian through the ringer (will update when I do), but so far is appears to work as advertised. I performed an integrity test first thing and it's functional in that regard. I've thus far used the pump from small puddles where the pre-filter cannot be fully submerged and have not had any issues (basically works as advertised), but have yet to pump from silty and dirty sources. I will say the water thus far tastes great and the act of pumping is fast and not strenuous. While pumping, you can see the 10% backflushed water exiting, so I assume that's also working without issue. The device is somewhat bulky, but really it's not much bigger or heavier than comparable products that don't purify (i.e. filter viruses). It includes a nifty little zippered cloth storage case as well. If the hose is wrapped tightly and neatly around the device, the pump handle can close over the rubbery hose end and hold the wrapped up tubes in place very conveniently. If the pre-filter and backflushing mechanism works in really silty, muddy sources as advertised (I don't see why it won't), then I'll likely have this device for many decades. It seems very sturdy and it's totally believable that it meets the advertised crush/drop/freeze tests. Any part that might be susceptible to long term wear (like the pump handle, tubes/pre-filter, etc.) appear to be, or clearly are, replaceable. In short, this revolutionary device is thus far working exactly as you'd expect it to from the Peru video, etc. and gives me the confidence to partake in much longer backpacking trips in the desert where adequate sources are rare and other pumps require a lot of babying. The convenience factor is through the roof on this product, and while everybody else is wasting daylight waiting on iodine tablets, finicky filters that require additional treatment for viruses and/or careful source selection, gravity fed filters, etc. I'm confidently plopping my Guardian in whatever dirty, nasty source I come upon, pumping for a few seconds, and then ready to go. As a result, I carry much less water, and thus weight, in general because I no longer have to be picky about where I'm getting my water. Lastly, one thing I do hear from people interested in the Guardian is "$350, that's awfully steep". As far as initial investment goes, yes, it is markedly more than other pumps/filters, but over the long run, iodine tablets can cost over $3500 for 10,000L of purification (and don't filter particulate). Other purification methods take time, require a lot more care an attention, break frequently (I'm looking at you, Steripen), require much more frequent filter changes, etc. Doing the math for my own personal needs, the Guardian comes out as by far the most economical and convenient product over the long run, but I encourage people to consider their own specific needs.
Date published: 2016-01-26
  • y_2017, m_5, d_19, h_3
  • bvseo_bulk, prod_bvrr, vn_bulk_1.0.0-hotfix-1
  • cp_1, bvpage1
  • co_hasreviews, tv_0, tr_53
  • loc_en_US, sid_891193, prod, sort_[SortEntry(order=RELEVANCE, direction=DESCENDING)]
  • clientName_rei-inc
  • bvseo_sdk, java_sdk, bvseo-4.0.0
  • CLOUD, getReviews, 389ms

In order to help compare this filter to other brands/types, what is the smallest size of particle, in microns, that this filter will remove? For instance, the First Need filter removes particles down to 4 microns.

Asked by: wildernesslovin
.02 microns
Answered by: giingerbreaddan
Date published: 2017-02-01

Interested in this product, but wondering why it was pulled from REI so quickly. Was there an issue with availability? Some other reason that you can share with us?

Asked by: PatCrash
As of July 2016, we are sold out of the Guardian Purifier and are unable to backorder at this time. Please check back later as we anticipate the item being available once we receive additional orders.
Answered by: REIservice
Date published: 2017-04-04

Can you fill an Osprey water bladder or another small mouth bottle with the MSR Guardian?

Asked by: JKuck
You can use the Guardian Purifier to fill any bladder or water bottle, even if the bladder or bottle does not thread into the Guardian Purifier.
Answered by: REIservice
Date published: 2016-11-17

I have just purchased the Guardian and tried it out on some very murky water after verifying the unit through a successful integrity test.  The filtered water was quite tinted in color afterwards.  Not at all what I expected.  Is this normal?

Asked by: Windyview
The Guardian filter is working as intended and tannins (tannic acid from decomposing plant material) in the water will appear with a color when filtered.
Answered by: REIservice
Date published: 2017-04-05

Can this be used to desalinate water?

Asked by: Pamela
This purifier does not remove salt from saltwater. We, unfortunately, do not carry desalinators.
Answered by: REIservice
Date published: 2017-04-20

Why was this item pulled? It's the best water filter on the market? Wish I could still buy top notch items at rei.. was waiting till my next 20% coupon to buy it, but it was gone by then.. 

Asked by: jrussell6
At the moment we are sold out of the Guardian Purifier. Please check back soon.
Answered by: REIservice
Date published: 2017-04-04

Can the MSR Guardian Purifier screw on to the threads of a MSR dromedary bag just like the purifier would to a Nalgene bottle?

Asked by: Ben H
This purifier does screw on to the threads of the MSR Dromedary Bag.
Answered by: REIservice
Date published: 2017-05-09

does this filter out chlorine and fluoride from water too?

Asked by: ljgw
​This does not filter out chemicals such as chlorine or fluoride.
Answered by: REIservice
Date published: 2017-04-20
  • y_2017, m_5, d_19, h_7CST
  • bvseo_bulk, prod_bvqa, vn_bulk_1.0.0-hotfix-1
  • cp_1, bvpage1
  • co_hasquestionsanswers, tq_13
  • loc_en_US, sid_891193, prod, sort_[SortEntry(order=NUM_ANSWERS, direction=DESCENDING)]
  • clientName_rei-inc
  • bvseo_sdk, java_sdk, bvseo-4.0.0
  • CLOUD, getContent, 42ms