MSR TrailShot Microfilter Review

© Richard Prideaux

Small and simple are the two words that instantly spring to mind when describing MSR's TrailShot water filter. This ultralight model is about the same size as a small bag of crisps, and looks more like a personal medical appliance than a piece of hiking hardware; but it delivers a lot for such a compact package.

Using the TrailShot in leafy North Wales  © Richard Prideaux
Using the TrailShot in leafy North Wales
© Richard Prideaux

First Thoughts

There isn't a lot to this filter. Once out of the packaging all you get is a pipe and something that looks like it can be used for blowing the dust off your camera sensor. I think that's part of the design intent – intuitive and simple, with little to break or lose when on a trip.

The pipe end is the intake, with a pre-filter that you submerge in clear-ish water. The other end is a handpump that pulls the untreated water through a second (0.2 micron) filter before literally squirting it out of the 'clean' end of the filter into whichever bottle, hydration bladder or receptacle you place in front of it - even straight into your mouth. It is that simple.

The numbers that go along with the MSR TrailShot are impressive for its tiny size and afordable £40 price tag – a 1L/minute flow rate, 2000 litres between cartridge changes, and an overall weight of only 142g. When wrapped up with an elastic band or strap it will just about fit into the chest or waist pouch on an ultra vest or rucksack, yet it seems rugged enough to survive some reasonably rough treatment.

It's got a flow rate of 1 litre per minute  © Richard Prideaux
It's got a flow rate of 1 litre per minute
© Richard Prideaux

Field Testin

There are actually a few things that you need to take into account when using this filter. The first is that you not only need to prime the filter by pumping it a few times, you also need flush out any water left in the system from the last use. The next is common to all filters – it doesn't matter how good the filter itself is if you can't keep the dirty water well away from the clean end and your water bottle. Both of these can be achieved with a bit of careful use and discipline, and a snap-shut cap covers the clean end of the filter. However I did still feel like the intake end of the hose was sitting perilously close to the clean end of the filter when the whole lot is packed away.

If you want a water filter that can keep up with your ultralight adventure pace without taking up too much room, then this is probably the best on the market at the moment

Floating the intake filter in a stream  © Richard Prideaux
Floating the intake filter in a stream
© Richard Prideaux

The intake can be easily cleaned if it gets clogged  © Richard Prideaux
The intake can be easily cleaned if it gets clogged
© Richard Prideaux

As above, this filter is really easy to use. I have passed it out to friends and clients without explanation to see if they could work it out for themselves – and so far, so good. As long as the water you are taking from isn't too cloudy or heavy with sediment then it should flow through the filter without much of a problem. The pumping is easy and fast, and the fast flow rate means that you aren't hanging around leaning over a stream or pool for too long.

As it's so small and unobtrusive I've found that rather than refilling a whole bladder I was stripping down the weight and going out with just the MSR TrailShot and a 1L bottle, refilling several times throughout the day as I passed suitable water sources. For runners and hill walkers looking to go light, the TrailShot's compact size and general convenience make it an attractive option.

As this is only a 0.2 micron filter than means it's suitable for catching harmful protozoa, like giardia and cryptosporidium, and bacteria like salmonella, but NOT viruses. It does meet the U.S. E.P.A. drinking water standards but you will need to carry additional water purification tablets if viruses are likely to be an issue (this is not generally a worry in the UK).

The hand pump is simple and intuitive to use  © Richard Prideaux
The hand pump is simple and intuitive to use
© Richard Prideaux

Here's what MSR say about this:

"Micron ratings aren't always the best way to gauge effectiveness. Test procedures for micron ratings vary so greatly that comparing them is misleading. In addition, micron ratings for filters do not tell you how the product will perform with actual bugs. There is an EPA Guide Standard for Testing Microbiological Purifiers, which describes how to test products to determine if they are removing or inactivating the proper number of pathogens in different types of water throughout the life of the device. When looking for a microfilter or purifier ask if the product has been tested according to the EPA Guide Standard and passed. For a microfilter, meeting the EPA Guide Standard means removing 99.9% of protozoa and removing 99.9999% of bacteria in all required water types. To be classified as a purifier, the device must meet the EPA Guide Standard for the removal of protozoa and bacteria as well as virus which must be inactivated to 99.99% in all required water types. All of the MSR filters and purifiers have passed the levels of inactivation required by the EPA Guide Standard with flying colors."

The difference between a 'filter' and a 'purifier' is also worth quoting:

"A filter actually removes matter and microbes from the water while a "purifier" can employ a variety of methods to disinfect the water (such as UV or MIOX® or combination system like the MSR Sweetwater® purifier). A purifier must meet the EPA Guide Standard for Testing Microbiological Purifiers, which requires inactivation of all three classes of microbes: protozoa, bacteria and viruses. Filters in general claim to remove only protozoa and bacteria, making it adequate for most travel in developed countries. Some filters alone can qualify as a purifier, but since they are filtering to such a small pore size, they tend to clog quickly. Essentially the classification as a "purifier" means that the device must be capable of inactivating viruses, as well as protozoa and bacteria."

If the intake filter becomes clogged it can be cleaned out in the field fairly quickly, and MSR recommend that the filter itself is cleaned and flushed through with clean water when possible.


Outside a lab it's always tricky to work out if a water filter is actually working - short of catching something nasty (thus, I guess, proving that it isn't!). You can however assess the design and weight, read the accompanying literature and decide if it's suitable for your intended use. For me the MSR TrailShot ticks a lot of those boxes. It's small, light, quick to use and seems to be rugged enough to survive an adventure or ten. For those reasons alone I will happily throw this filter in a bag for a wild camping trip or even a fast-and-light long mountain day where water weight would slow me down even more than my genetics.

The 0.2 micron filter size is starting to become the norm for commonly available water filters, and carrying sterilisation tablets isn't too much of a weight penalty if viruses are likely. In that situation you could even use the TrailShot as a first-stage filter before boiling the water.

If you want a water filter that can keep up with your ultralight adventure pace without taking up too much room then this is probably the best microfilter on the market at the moment.

MSR say:

Clean water all day—without the weight. That's the advantage the TrailShot Microfilter provides. Designed to hide in stash pockets and deploy quickly, this tiny water filter lets you drink directly from sources along the trail for instant hydration, and fill your vessels with clean water. Easy one-handed operation filters one liter in a mere 60 seconds, so you can get back on the trail quickly and moving again. At just 142g (5 oz.), the TrailShot water filter is the ultimate filter for fast-paced, high-mileage adventurers, like trail runners, hikers, fast-packers and mountain bikers.

For more info see

  • Price: £40
  • Weight: 142g
  • Tested: Meets U.S. EPA drinking water standards* and NSF protocol P231 for removal of bacteria (99.9999%), protozoa (99.9%), and particulates
  • Pocket-Sized & Light: Like small water bottles, energy chews, mini bike pumps, and tubes, this 142g (5 oz.) filter disappears in stash pockets
  • Instant Hydration: Drink directly from the source—without lying in the dirt—and refill your bottles or hydration reservoir with clean water
  • Quick-Deploy: Zero set-up and simple one-handed operation fills 1-liter bottles in 60 seconds
  • Simple to Clean: A few shakes helps restore flow rates in the field; no tools required
  • Made in USA

*U.S. EPA Guide Standard and Protocol for Testing Microbiological Purifiers

Richard Prideaux head shot  © Richard Prideaux

About Richard Prideaux

Richard Prideaux is the owner of established North Wales outdoor skills training and activity business Original Outdoors. He spends on average one night per week sleeping in a forest, up a mountain or on a beach somewhere in the UK and further afield and the rest of the time teaching navigation, foraging, tracking and other wilderness skills.

For more info see

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2 Jun, 2017
Recently bought one of these and I agree it is light and packs up small. I've taken it out on two overnighters but haven't actually needed to use it yet, so only comments about size and weight so fat! I googled to find one and bought it from a shop in Lancashire called Tamarack Outdoors. I'm sure there are loads of great shops out there you could get one from (although I had gone to my local GO with their website saying they had them in stock to find, annoyingly, they didn't) but Tamarack were super fast in getting it to me and had a very good price on the filter.
2 Jun, 2017
Tamarack have always provided with decent service.
2 Jun, 2017
Trekitt £31 1St class service
2 Jun, 2017
Price matched to Go Outdoors, £28.50 and they even had 1 in stock Result.....
3 Jun, 2017
Another vote for Tamarack and their service. Well worth the diversion off the M6 for a store visit.

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