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MSR Guardian Water Purifier Review

MSR Guardian Water Purifier Review

MSR Guardian Water Purifier

Treatment Capacity
Ease of Use

Best Water Purifier Available Today

The MSR Guardian is the most sophisticated and effective water purifier available today. Self-cleaning, it has a high flow rate, and generates remarkably good tasting water. While it is an excellent tool for backcountry use and international travel to countries with suspect water, it's also quite a nice product to have on hand for emergency preparedness at home.

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The MSR Guardian is a first-class water purifier that removes viruses, bacteria, protozoa, dirt and silt from backcountry and international water sources. Weighing just 17.3 ounces, the Guardian has a self-cleaning filter that constantly purges itself while you filter water so you never have to backflush or scrub the filter element. It also has an exceptionally high flow rate of 2.5L per minute, making it ideal for individual or small group use. You can even perform a field integrity test with the Guardian purifier to make sure it’s still working correctly after it’s been accidentally frozen or dropped. That’s unique! Let’s take a closer look.

Specs at a Glance

  • Removes:
    • 99.9999% Bacteria (E.coli, Salmonella, etc.)
    • 99.9% Protozoa (Giardia, Cryptosporidium, Amoeba, etc)
    • 99.99% Viruses (Hepatitis A, Norwalk)
  • Type: Pump Water Filter
  • Flow Rate: 2.5 L per minute
  • Bottle/Bladder Compatibility:
    • 1L Wide-mouth Nalgene Bottles
    • Wide-mouth Nalgene Soft Canteens
    • Wide-mouth MSR Dromedary and Dromlite Bladders
  • Filter Lifetime: 10,000 liters, replacement filters sold separately
  • Field Weight: 17.3 oz

Water Purifiers vs Water Filters

The  Guardian is a water purifier which is different from being a water filter because it can remove viruses in addition to bacteria and protozoa. Viruses are infectious microbes that are smaller than bacteria or protozoa and the pores in regular water filters aren’t fine enough to trap them. The Guardian, for instance, can remove pathogens down t0 .02 microns in size, or about is 10 times smaller than a comparable water filter like the MSR Miniworks EX water filter, which can only remove organisms down to 0.2 microns in size.

While Steripen UV lights can neutralize viruses, bacteria, and protozoa, they can’t remove suspended solids or dirt from water like a filter or purifier. Chemical purification in the form of chlorine dioxide or iodine tablets can also purify water, but the treatment times can take up to 4 hours and isn’t instantaneous or as taste-free as the water processed by a purifier.

MSR Guardian Components
MSR Guardian Components

Pump Style Water Purifiers

Pump-style water purifiers are better than UV or chemical purifiers for processing from turbid and cloudy water sources like snowmelt, beaver ponds, and cattle troughs because they can filter out particulates in addition to pathogens. The pressure provided by a pumping action is required to force clean water through the walls of a filter element to remove foreign matter.

The Guardian has two hoses, an intaked hose, and a dirty water hose that expels what that's been used to backflush the purifier element
The Guardian has two hoses, an intake hose, and a dirty water hose that expels water that’s been used to backflush the purifier element.

Hose and Pre-filter

The MSR Guardian comes with two hoses, a pre-filter, and a float. The first hose is an intake hose that pulls water from the pre-filter into the purifier. The second hose expels dirty water and backflushes the purifier filter every time you pump water through the Guardian, cleaning and removing trapped impurities in order to maintain a high flow rate. Having an intake hose also lets you obtain water from hard-to-reach water sources such as shallow seeps, boulder-covered springs, water flowing underneath obstructions like snow and ice, or down steep stream and river banks. It also lets you sit in a more comfortable position while you filter water, which can be a godsend if you have to do it for a group.

The pre-filter is designed to block or remove as much muck (soil, sand, and suspended solids) from the water as possible before it reaches the purifier, which is responsible for removing microorganisms. Having a pre-filter is extremely useful if you need to get water from sources that are cloudy or have a lot of suspended solids in them like puddles, cattle troughs, beaver ponds, creeks, and snowmelt because it increases filter life and decreases filter maintenance.

The pre-filter is suspended under a foam float so it pulls in water from below the surface
The pre-filter is suspended under a foam float so it pulls in water from below the surface.

The Guardian pre-filter is suspended from a foam float and oriented so that it pulls water from just below the surface of a water source, where it’s usually the cleanest. The foam float has two hoses attached to it, the intake and outlet hoses, in order to keep both hoses under control and manageable. The pre-filter hangs below the float at a right angle so it can reach water under the surface. The float and pre-filter work best when they’re used to extract water from a still pool, but have a tendency to flip over in moving water, which can reduce the Guardian’s flow rate because less water is reaching the filter element.

The Guardian screws directly onto wide mouth water bottles and reservoirs and is compatible, out of the box, with plastic Nalgene style bottles, Nalgene soft canteens, MSR Dromedary, or MSR DromLite water bladders. The base of the purifier also has a nipple that you can attach a hose to if you want to output water to a small mouth bottle or reservoir. Unfortunately, an extra hose is not provided with the unit for this purpose.

The prefilter requires minimal water depth to work although you may need to position it by hand
The prefilter requires minimal water depth to work although you may need to position it by hand

The Guardian is super easy to use. You just screw it onto the bottle or reservoir you want to fill, drop the float and pre-filter in the water and start pumping. It doesn’t take much pressure to pump and fills your bottles quite quickly. You just have to be careful to keep the bottom section which screws onto your bottles clean and out of contact with un-purified water. The Guardian comes with a screw-on clean side cap for this purpose, but you have to be careful to keep it clean as well, between uses.

When you’re finished processing water, remove the float and pre-filter and pump the filter a few more times to empty any residual water trapped inside. Then screw on the clean side cap, wrap the hose around the pump, and store it in a dry bag or external pack pocket where it can drip dry.

Potential Issues

Fine Silt

The Guardian’s greatest strength, its .02 micron pore size, is sometimes its greatest weakness if you need to filter water that has very fine suspended silt in it, because it can clog the filter element and make pumping water through it impossible. I haven’t experienced this myself because we have very clean water where I hike, but I’ve read about it occurring elsewhere. If silt is an issue in your water supply, the best solution is to collect water in a separate container and let it sit for a while so that the silt settles out. You would need to do this regardless of the purification method you use because silt makes it harder to purify water with UV or chemicals. Another option is to filter the water using a water filter that has a larger pore size like the MSR MiniWorks EX, and then use UV or chemical purification to kill off the virus pathogens in the water in a second purification step.


Most hollow fiber tube water filters (like the Guardian) are damaged if they freeze and should be replaced. The Guardian can be frozen but must be completely re-thawed before use. If you do accidentally freeze it, it’s best to perform the simple purifier integrity test specified in the Guardian manual, before you resume using the filter. This test can be performed in the field, provided you have a clear wide-mouth bottle with you.

The base of the Guardian screws on to wide mouth bottles, but you can also run a hose to a small neck bottle if that's what you use
The base of the Guardian screws on to wide mouth bottles, but you can also run a hose to a small neck bottle if that’s what you use

Comparable Pump Water Filters and Purifiers

Make / ModelWeightPore SizeFilter MediaFilter LifePriceReplacement Filter
MSR MiniWorks EX17 oz0.2 micronCeramic2000L$85$40
MSR Guardian17.3 oz0.02 micronsHollow fiber10000L$350$180
MSR HyperFlow7.8 oz0.2 micronHollow fiber1000L$100$40
Katadyn Hiker11 oz0.2 micronGlass Fiber750L$75$50
Katadyn Hiker Pro11 oz0.2 micronGlass Fiber750L$85$50
Katadyn Vario16 oz0.2 micronCeramic, Glass Fiber2000L$95$45
Katadyn Pocket19 oz0.2 micronCeramic50000L$370NA
General Ecology First Need16 oz0.4 micronGlass fiber680L$109$50


The MSR Guardian is the most sophisticated and effective water purifier available today. Self-cleaning, it has a high flow rate and generates remarkably good tasting water. While it is an excellent tool for backcountry use and international travel to countries with suspect water, it’s also quite a nice product to have on hand for emergency preparedness at home, especially if you live an area prone to flooding or other natural disasters. If you like great tasting water and don’t want to wait for it, the Guardian is a safe way to get it.


  • Self-cleaning
  • Removes viruses as well as bacteria and protozoa
  • Compatible with wide-mouth Nalgene-style bottles and reservoirs
  • Pre-filter helps minimize silt and suspended solids before they reach the filter
  • Replaceable Filter
  • Field Maintainable
  • Easy to maintain and store when not in the field


  • Heavier than other alternatives
  • Still have to carry a wet hose after filtering
  • No adaptors/hose provided for narrow-necked bottles or reservoirs

Disclosure: MSR provided the author with a Guardian for this review.

Editor's note: Help support this site by making your next gear purchase through one of the links above. Click a link, buy what you need, and the seller will contribute a portion of the purchase price to support SectionHiker's unsponsored gear reviews, articles, and hiking guides.

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  1. The MSR Guardian seems like a well designed piece of equipment that offers features few if any other treatment options can match. However under dislikes, I would add that it is quite expensive. If you need to purify could carry a Sawyer Squeeze and Steripen both and still save half a pound and a few hundred dollars.

    • While it is expensive, you’d be waiting a long long time to be able to purifiy more than 1 liter of water since the Steripen can only do 1 liter of water at a time and a sawyer isn’t exactly fast. Buy whatever floats your boat.

  2. I’ve been using one of these for about a year and am quite happy with it. It is amazing how fast it is! Wait for Campsaver to have a 20% off sale (every other week it seems) and save $70.

    • Exactly. I’m very tempted to switch to one of these guys myself, especially in a group. The ease of use over a sawyer or steripen is really pretty impressive, despite the weight increase. For volume filtering it is just incredible.

  3. I’ve been toying with the idea of one of these to use with my regular backpacking crew. I’ve become “water treatment guy” for the group and this would probably come close in weight to what I currently use, and likely quicker. I notice that REI and MSR are selling it for around $260 right now, which makes me wonder if it’s about to be discontinued or replaced by an updated model.

  4. it is a mighty bit of kit.
    filters water that other filters get clogged by.
    saved Martin and I in the Dales.
    Very expensive and quite heavy, but it delivers on all fronts.

  5. Bought mine with the idea of using it in a group setting. Heavy and expensive, but I’d buy again. It has it’s place in a group setting or when I know the water source(s) is going to be really sketchy or limited. Works really well paired with a Dromedary bag. For those commenters considering it for group use, yeah..definitely. Do it, especially if it’s on sale.

    For smaller groups (six/eight or less) I usually just use a gravity filter. Saves a bit of weight over the Purifier/Dromedary combo and nearly as convenient. By myself, I just carry a Sawyer and perhaps some chemical tabs.

    The little foam floater thingy at the intake doesn’t work though. Seems to always want to rotate the intake out of the water. I always wind up having to hold it under. Small detail though.

  6. No thanks at that price I will continue my affair with the First Need XLT and my 20 + year old Deluxe Model at about $100.00…. MSR trying to rip off the hikers with that high price…..

  7. I picked up one of these during the REI Labor Day Sale at significant discount, in part after reading your review. I am curious if after reviewing it, you might be adding it to your best water filters list or if you still consider it overkill for backpacking?

  8. So the freezing water filter malfunctioning thing is an issue for me. What are my options for water purification that can handle below freezing temps for extended periods of time besides the tablets? Do the UV light pens work in the cold? Thanks.

  9. I use an Everpure Scout, very fast, much much cheaper ($50?). Has no back flush so I carry a spare filter cannister. Weighs a couple of ounces.

  10. Correction to my comment above, I use a Rapidpure Scout (not an Everpure). Filter and spare cartridge combined cost $50. Weighs an ounce, maybe two.

  11. I’ve been using the First Need Deluxe for about 25 years or longer…. It was the ONLY PURIFIER on the Market until MSR arrived a year or so ago after a Government Contract win…. The First Need Deluxe, a simple hand Pump Operation, via a Canister and was the original Unit to fit on the Nalegene Bottle that many years ago and way ahead of MSR. Now called the First Need XLE Elite it still costs near $100…. saving you on average some $250.. Sorry but MSR is ripping you off in my opinion….

    • The First Need was the first water purifer I used and I still have it. But the Guardian is a better product. It’s self cleaning for one, which means the filter will last a long long time.

      • Ab.so.lutely. The First Need was amazing for its time, but I found it to choke on southern clay silt and western mountain silt. I have used the Guardian in the South, but not yet in the West. I will do so before long and then I will be able to say whether I find it easier in that environment.

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