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Guardian Purifier System

4.04 out of 5 stars
125 Reviews
Color:One Color



Why We Like The MSR Guardian Purifier System

Drinking straight from crystalline mountain streams is nice in principle, but a lot less awesome when we end up running for the bushes every five minutes for the rest of the trip. There are plenty of ways to prevent waterborne bummers, but none that we find as effective, easy to use, and reliable as the MSR Guardian Purifier System.


  • Pump-action purifier for backpacking and trekking
  • Self-cleaning design for easy maintenance in the field
  • Effective against protozoa, bacteria, viruses, and particulate
  • Water bottle adapter ensures convenient refilling
  • Item #CAS008I
Purifying Element
Hollow Fiber
protozoa, bacteria, viruses, particulate
Pore Size
0.02 micron
Cartridge Life
10,000+ L
2.5L / min, 30/35 strokes / L
Field Cleanable
water bottle adapter, cartride replacement indicator
8 x 5in
Claimed Weight
1lb 1oz
Manufacturer Warranty
limited 3 years

Overall Rating

4 based on 125 ratings

Review Summary

1 Stars - 17 reviews
2 Stars - 8 reviews
3 Stars - 8 reviews
4 Stars - 12 reviews
5 Stars - 80 reviews

What do you think about this product?


Selecting an option will reload the available reviews on the page
1 out of 5 stars

April 2, 2024

Not a product to stake your life on

This product has a certain shelf life before the filter dries out making the purifier useless. I bought my purifier and put it away (3 years) in an emergency kit. Then I took it out to try the integrity test which it failed. In fact the filter has dried out. There is NOTHING in the manual that states how long this product can stay dry after purchase before the filter dries out. I have lost my faith in MSR as well as a great deal of money.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

5 out of 5 stars

March 4, 2024

Reliable, use it correctly

I have used this product multiple times and have not experienced any issues. Watch videos on line to ensure you know how to use and clean it. What’s nice about this is that it can quickly filter large quantities of water and it tastes great. So if you are hiking or backpacking with a larger group you can serve many people and share the load.

David D
1 out of 5 stars

November 13, 2023

Great filter until it fails

I bought the Guardian a few years ago planning for a trip that never happened, so it stayed unused and untouched in storage for about 3 years. Then I took it on a hiking trip through Lapland, where the seal failed on the first day during the filling of the second 1l bottle. I had the instructions with me and went through them as described, so this was not user error. This filter is a flawed design with much potential and reading the other reviews, MSR didn't fix the problems yet. If they ever do I might give it another try, simply because the first bottle filled wonderfully quick. I'm very disappointed with this product.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

1 out of 5 stars

November 1, 2023

Broke since day 1

I bought it two days ago as a present for my wife's birthday to use it in her upcoming trip to Nepal. When I tested it, it start leaking. I tried to disassembled it by hand just to find out that the end nut was broken. Very disappointing. I'm wondering about those military standards...or it is just a trick to by very expensive and not reliable kit. I will ask the shop for return but I doubt I will buy again this purifier.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

2 out of 5 stars

September 21, 2023

Too risky and poor service

I bought the Guardian for treks to faraway places. With the bottom gasket leaking and the real possibility of some moving parts breaking or getting lost I have decided that this is too risky as a sole source of clean water. Probably the GUARDIAN GRAVITY WATER PURIFIER would be a far better option (but I now don't have the money). MSR have NEVER responded to my emails. It even took me one year after ordering the Guardian to receive it. Spare parts or spare filters might be too much to hope for.

Jim B.
a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

3 out of 5 stars

September 18, 2023

Not reliable enough

I have the Guardian Purifier (I had to wait over one year to get it). Water leaks out from the lower gasket and from the reviews for this product it seems that we will have to look out for certain plastic pins to fail as well. In light of this we will probably not take this Purifier on our backcountry trips. Here in Australia you can't even get replacement filters or parts. I wish we had waited for (never knew it was coming) for the Guardian Gravity Purifier that would it seems eliminate all of the above problems. This is also a problem for Australians because this item is not available. When you try to buy from overseas they tell you they are not allowed to send to Australia. Ever heard of Catch 22? Thank you.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

2 out of 5 stars

September 11, 2023

Great When It Works...But You'll Want to Take a Backup

TAKE A BACKUP! We bought the Guardian wanting the best purification solution that would give us peace of mind no matter where we traveled. Put it to work for the first time on a short trip to Lake Superior, MI backcountry where it was likely overkill. I had read the reviews on this site, on REI's and on various other reputable sources and heard enough good things to give it a shot. The Guardian is terrific when it is working properly, fast flow rate and smart design that make it simple to use. But, you'll notice that many of the negative reviews point out that there are specific failure points. I am glad I paid attention to them and brought a smaller back up filter and chem treatment because on our last night in the woods the o-ring failed and water was pouring out of the bottom of the filter assembly from all sides. Needless to say, "disappointed" doesn't accurately describe my reaction. I hope MSR can make this situation right for me personally, and more importantly fix the robustness issue or at least issue guidance on how to prevent it from happening in the future.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

3 out of 5 stars

August 31, 2023

Love my guardian, MSR customer service has left me hanging

I've had my guardian for a couple years and it's absolutely the best filter/purifier I've used. The filter itself is 5 stars. However, on my last backcountry trip, the pre-filter piece snapped off (it's just a plastic joint, so it didn't take much) and I've submitted two repair/warranty tickets. MSR has not replied to either of my warranty tickets (despite confirmation that they were received). All I'm asking for is a new pre filter piece. At this point, I'd gladly buy a replacement piece but I can't even find one anywhere in Canada.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

2 out of 5 stars

July 30, 2023

Loved it until it failed in the backcountry

I have owned this purifier for around five years and even though it is heavy and very expensive, I have always loved it. That is until my recent trip where it completely failed by leaking unfiltered water from the plastic base rendering it completely useless. This could have turned into a dangerous situation if we didn’t have a backup filtration plan. After a quick internet search it appears that this is a common failure point. While the recommend fix of unscrewing the black plastic base to leave a gap seems to resolve the issue, I am not sure I would be comfortable relying on this product anymore. It clearly seems to be a design flaw that MSR should work to resolve given that this filter is one of the most expensive products on the market.

a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site

4 out of 5 stars

July 20, 2023

Great unit. When I first

Great unit. When I first used it, the pin that holds the handle fell off and I spent 20-30 minutes looking for the 2 piece pin in the stream i was filtering water from. Now I know to make sure to check on the pin so it doesn’t fall off again. the pin always wants to fall off on its own and then i have to click it back closed again. Other than that issue, the filter works great

James S.
a Cascade Designs brand site

Originally reviewed on a Cascade Designs brand site