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I have been using the MSR Guardian Purifier Pump for the last four years, using it to purify water on all my long distance walks.

I have used a number of different water filters over the years but since purchasing this one, it’s been with me on every long distance hike I’ve done and most overnight trips: the TGO Challenge, Cape Wrath Trail, LEJOG and Dover to Cape Wrath to name a few.


The MSR Guardian Purifier Pump is a water purifier rather than a water filter. The difference is that water purifiers can remove viruses from the water as well as bacteria, protozoa and dirt. Water filters aren’t fine enough to trap viruses. You can purify water chemically using tablets, but this takes a lot longer and they can make the water taste funny. I also don’t like adding unnecessary chemicals to my body.

The MSR Guardian was originally designed for military use, so it is really well made, easy to use, maintenance free and even cleans itself. This is extremely reassuring on long walks.

This is probably the safest water purifier for travelling anywhere in the world. It removes all the stress of getting ill from the water. You might think that this level of purifying is only really needed when trekking in developing countries, but it is just as important when hiking in really popular (and highly populated) areas of the UK.

The MSR Guardian is probably overkill for high remote hikes in the mountains of Scotland, but I’m often walking in lowlands where there’s a lot of cattle and sheep. This means more chance of bacteria in the water and this is the best purifier I know of for removing them from the water.

The MSR Guardian Purifier Pump meets the NSF Protocol P248, which is the testing standard used by the US military.


Yes, the pump is heavy. Lightweight hikers may flinch, as it weighs 490g, which is considerably more than other systems.

However, because I’m able to get water from a wide variety of sources, even dirty water, I don’t need to carry as much water with me. It’s so quick and easy to filter water as I need it. Carrying less water saves weight, which mitigates the pump’s weight.


The MSR Guardian Purifier Pump is expensive – clicking on the link will take you to the latest price on Amazon.

However, the cartridge allows you to filter up to 10,000 litres of water. This means that in the long run it is quite cost-effective. Most other popular water filters allow up to 1,500 litres per cartridge.

You have to balance the cost of the MSR Guardian against the reassurance of always getting safe, clean water no matter what. I’ve found that it helps enormously when choosing wild camping spots, especially in lowland areas.

Ease of use

MSR Guardian Purifier Pump with the Nalgene bottle attached

The threads in the bottom of the MSR Guardian fit a Nalgene bottle as shown in the picture above.

However, I don’t usually carry one because they are heavy (175g). I carry Platypus or Evernew flexible bottles instead, because they are so much lighter and roll up small when they’re not needed.

These flexible bottles don’t screw on to the pump so they’re a little harder to fill. I have to hold the bottle in place to fill it, but it’s not too difficult because the outlet for the clean water is small as shown in the picture below.

MSR Guardian showing the outlet for clean water

The purifier pipe wraps nicely around the pump keeping everything tidy. It protects the pipe from kinking. It all fits in its own tough bag, protecting it from damage. This is very important when you’ve paid so much money for it!

Overall verdict

I think the MSR Guardian Purifier Pump is worth every penny. It’s so quick and easy to use, the filter cleans itself and its longevity helps justifies the weight and cost. I’ve never had the filter clog or reduce flow in any way and I’ve filtered hundreds of litres of water.

I often hike with my family so I need to filter a lot of water and need to know it’s safe. The fact it only takes me a few minutes to filter enough for all of us is worth a lot to me.

Highly recommended.

Check the price of the MSR Guardian Purifier Pump on Amazon

Further reading

Read about how the MSR Guardian Purifier Pump meets the NSF Protocol P248 testing standard used by the US military.

My Gear Lists

My 1100 mile Dover to Cape Wrath walk full gear review

My 11 Leave No Trace Wild Camping Rules

Disclosure: Wildwalkinguk is a blog run by myself and my wife in our spare time, and we pay for its running costs ourselves. We do have some Amazon affiliate links and adverts on the site. If you click on these adverts or links and buy what you need (it doesn’t have to be the item we’ve linked to), the company will pay a small commission to us. This money goes towards the costs of hosting the blog. We would be extremely grateful if you could consider using our links when you next need to buy something from our advertisers. Alternatively, you can buy us a coffee here. Thank you so much for your support. Mark and Emma.

3 Replies to “MSR Guardian Purifier Pump”

  1. I like that it you can use really dirty water as a water source if you have this purifier, but I’ve always been curious – does it improve the taste of the water?

    1. The water tastes OK after filtering it. The only time that it’s not tasted like water should, was when it had a soap like taste. I’d filtered water down river from a town and must have filtered some really dodgy water with chemicals in. The filter is not meant/designed to clean/purify water with chemicals in.
      Thanks for message.

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