Bottom Line
The MSR Guardian is the 4×4 pickup truck of water filters. It’s the sturdy, dependable workhorse that handles the toughest jobs with ease. The Guardian not only filters water but also purifies it, removing nearly all harmful pathogens.
The only thing it lacks is a carbon filter to eliminate some chemicals and heavy metals. The Guardian complies with strict protocols used by the military for “worst case scenario” water sources, but we also test it ourselves by pumping dirt, silt, mud, and anything else we can find through it. Thanks to its self-cleaning mechanism, the Guardian had the best flow retention out of all the filters we tested.
Because the Guardian is more of a niche filter designed for challenging scenarios, it’s not the best choice for casual or ultralight backpackers. Its sturdy casing is quite heavy, as is its price. However, when you face extremely hazardous water options, there’s no price you can put on your health and well-being.
How We Tested
We tested the limits of this water purifier with the nastiest water we could find. We pumped it full of mud, silt, and sand to see how well it would perform in the harshest conditions.
Quick Specs
MSR Guardian
Best Filter for Purifying the Worst of the Worst Water
CleverHiker Rating: 4.6/5.0
Price: $390
Weight: 1 lb. 1.3 oz.
Flow Rate: 2.5 L/min
Filter Pore Size: .02 microns
Lifetime Volume: 10,000 L
Pros
- Rated for international backpacking
- Great flow rate
- Very durable
- Self-cleans as it filters
- Purifies water (including viruses)
Cons
- Very heavy/bulky
- Very expensive
Water Quality
The water quality produced by the MSR Guardian is absolutely tip top. It not only filters out bacteria, protozoa, parasites, sediment, and microplastics; it also purifies the water by killing viruses. The latter is a crucial protection when traveling in developing countries or heavily traveled backcountry areas. The purification quality of the MSR Guardian meets NSF protocol P248, or the U.S. military’s standard for treating the worst-case water sources.
Needless to say, the Guardian also removes the flavors caused by many contaminants from the water. It transforms even the nastiest sources into drinkable water you would be happy to have coming out of your tap at home.
Ease of Use
The Guardian takes slightly longer to set up than rapid squeeze filters, but it is still easy to operate. It’s ready to use in just about 30 seconds.
The process begins by unscrewing the bottom cap and unraveling the hose, being careful not to contaminate either part with dirty water. The clean end of the filter screws securely onto a wide-mouth Nalgene bottle, effectively preventing any spills. Alternatively, you can aim the filter at the container of your choice. Then, just drop the pre–filter into the source and start pumping.
The long handle offers ample leverage for pumping, even when silty sources challenge the filter’s limits. When the pre-filter is sufficiently wet, it blocks air from entering, allowing the filter to pump water even from a shallow puddle.
Treatment Time
The MSR Guardian is the fastest water filter on our list. It filters water nearly as quickly as you can pump, reliably filtering a liter in about 30 seconds. In other words, it takes roughly 40 pumps to filter one liter.
Dirty water will slow down the filter time temporarily. After filtering about two and a half gallons of muddy, silty water, the next liter of clean water only took about 50 seconds. Thanks to the filter’s self-cleaning mechanism, it returns to its normal filtering rate after a few liters of fresh water.
Weight
The biggest drawback of the MSR Guardian purifier is its weight and bulky size. It weighs about 1 lb. 9.4 oz, which far exceeds ultralight standards for a water filter, but if you know you’ll be encountering worse-case water sources, you’ll be glad to have it.
When it’s all packed up, the Guardian is about the size of a one-liter wide-mouth water bottle. All the components are conveniently stored on the filter itself – the cap screws onto the bottom, and the hose wraps neatly around the housing. They even include a sturdy, durable carrying case, although it’s not necessary to pack it away neatly.
Maintenance & Longevity
Maintaining and cleaning the Guardian is simple. It needs no extra steps other than pumping water through the filter. The Guardian automatically cleans itself with each pump stroke, so there’s no need for backflushing or filter scrubbing. If you look at the hose, you’ll see an input side for clean water and an output side for dirty water. You can even see the filter expel dirt and sediment as you pump.
The Guardian is as durable as it is hassle-free. It can withstand drops up to six feet on concrete (we double-checked) and can be frozen. Just make sure you don’t pump any water through it until it’s fully thawed. The filter cartridge has a lifespan of over 10,000 liters and can be replaced when it’s spent instead of buying a whole new unit.
The filter is designed for servicing in the field, and if you ever doubt its effectiveness, there’s a purifier integrity test you can perform to ensure it’s still functioning. The test can easily be done in the field as long as you have a Nalgene and some water.
Should You Buy the MSR Guardian?
Because of its high cost and bulky size and weight, the Guardian is best for backpackers dealing with the worst water sources. However, in these cases, there is no filter more suitable.
The Guardian is specially designed to filter out viruses along with common contaminants like bacteria, parasites, and sediment. There’s just not much that can pass through its tiny pores.
Another advantage of its size and cost is its durability and easy maintenance. The revolutionary self-cleaning mechanism makes filtering simple, no matter the water quality.
Ultimately, we wouldn’t recommend the MSR Guardian for most budget backpackers or those trying to save weight. However, for travelers in developing countries or dealing with the worst water sources, the Guardian is essential gear.
What Other Water Filters Should You Consider?
For some more affordable and lightweight water filters, check out our complete guide to backpacking water filters.
Katadyn Hiker Microfilter Review: If you like the idea of a pump filter for shallow water sources but don’t need the Guardian’s features, the Katadyn Hiker is a lighter and cheaper choice.
Aquamira Review: Aquamira is a great treatment option that also kills viruses. It is much lighter and more affordable, but is best suited for deep, clear water sources. Collecting water isn’t as easy as pumping, and it doesn’t remove sediment.
