MSR
MSR Guardian Purifier Pump
- Protection: 10/10 What it removes from water, and how well that is proved.
- Flow rate: 9/10 How fast clean water comes through when it is new. Real flow drops as it clogs: see Ease of use.
- Weight: 2/10 How much it adds to your pack.
- Ease of use: 8/10 Filling, squeezing or pumping effort, how fast it clogs in peaty or silty water, and how easy it is to clean.
Trips abroad where viruses are a risk, and expeditions
- Type
- Pump
- Removes viruses
- Yes
- Flow
- 2.5 L/min
- Weight
- 490 g
- Pore size
- 0.02 µm
- Rated life
- 10000 L
Where to buy
Trekitt £234.90 In stock. Free delivery. Page offers Notify me when available. Free next-day delivery over £65.
View at shop: TrekittUltralight Outdoor Gear £228.99 Out of stock. Shown with an RRP of £269.99. Free tracked UK delivery.
View at shop: Ultralight Outdoor GearWildBounds £229.95 Out of stock. Free UK delivery over £50.
View at shop: WildBoundsPrices checked 8 Nov 2026 on each shop's own page; shops can change them. We earn no commission on these links; shops are listed by price. More
Our ratings (out of 10)
1 to 10, compared with the whole market. Each says what it's based on. How we score
Protection
From maker's figures 10/10What it removes from water, and how well that is proved. 10: The best you can buy for this.
0.02 µm advanced hollow-fibre cartridge. MSR says it meets NSF protocol P248, the US military standard, for viruses, bacteria and protozoa from worst-case water: all three, to a named standard, so 5. OutdoorGearLab reports third-party SGS Labs tests that removed over 99.9% of each contaminant tested. UK hill water seldom needs virus removal, so 4 would do; the extra is a bonus for travel abroad.
Flow rate
From maker's figures 9/10How fast clean water comes through when it is new. Real flow drops as it clogs: see Ease of use. 9: Among the best you can buy for this.
MSR gives 2.5 L/min (about 35 strokes a litre), in the 2.5 L/min and over band. Better Trail found this matched its experience over three weeks. Testers measured less: OutdoorGearLab averaged about 2 L/min (30 seconds a litre) and never reached 2.5, and Switchback Travel took three to four minutes for four litres, which would be 4. Banded on MSR's figure.
Weight
From maker's figures 2/10How much it adds to your pack. 2: A weak point.
490 g (MSR), in the 450 g and over band. OutdoorGearLab weighed the whole kit with its bag at 581 g.
Ease of use
From reviews 8/10Filling, squeezing or pumping effort, how fast it clogs in peaty or silty water, and how easy it is to clean. 8: Clearly better than most.
Switchback Travel (5) found it extremely easy to set up and use, with no cleaning needed even in murky water. Better Trail (4) found the pump smooth and easy but noted the float on the intake hose takes a few sessions to get right. Backpackers.com (4) found it easy to use, with the float annoying until set at the right angle. UKC (4) called it easy and a pleasure to use. OutdoorGearLab scores ease of use 7 out of 10 (3): easy setup, but long, tedious pumping and a pre-filter that slows flow if it sits wrong. Average 4 out of 5, so 8 out of 10. Switchback and OutdoorGearLab are two points apart.
Reviewers disagree on this.
What reviewers say (out of 10)
Ratings marked * are from reviews and are not part of the trip score. They are reviewers' scores, not our own measurements. How we score
Durability*
Reviewers' average 7/10How well the bag, housing and fittings hold up over months of use.
5 reviews on durability, e.g. "the o-ring started to leak at the bottom and it became unusable for the rest of the trip.".
Reviewers disagree on this.
In short
Good for
- Trips abroad where viruses are a risk, and expeditions
- Groups of three or more who need litres of water quickly
- Murky or silty water that clogs squeeze filters
- Winter and frosty nights: MSR says it withstands freezing
Strengths
- Removes viruses as well as bacteria and protozoa (NSF P248, MSR)
- Self-cleaning pump flushes the filter on every stroke, so no backflushing (MSR; Switchback Travel and Better Trail found flow stayed steady)
- MSR says it is engineered to withstand freezing and a 1.8 m drop onto concrete
- Rated to 10,000 L, with a cartridge replacement indicator
- Rated 2.5 L/min, about 35 strokes a litre
- Screws onto wide-mouth bottles and MSR bags
Weaknesses
- 490 g (581 g with its bag in OutdoorGearLab's weighing), the heaviest filter in OutdoorGearLab's test
- Not hands-free like a gravity filter
- The float on the intake hose can sit on its side and stop it drawing water (Better Trail, Backpackers.com)
- OutdoorGearLab averaged about 2 L/min against MSR's 2.5 L/min
- OutdoorGearLab's pump had its piston nut break after minimal use; MSR replaced the part under warranty
Sources
We haven't tested this ourselves. Every score comes from these specs, tests and reviews.
ShowHide sources (10)
- MSR: Guardian Purifier, specs
- Switchback Travel: MSR Guardian Purifier review (Peru and Mongolia)
- OutdoorGearLab (Trish Matheny): MSR Guardian Purifier Review
- Better Trail: MSR Guardian Purifier Review (three weeks in Kyrgyzstan)
- Backpackers.com: MSR Guardian Purifier Review
- UKC Gear (Toby Archer): Guardian Water Purifier from MSR (UKC says it receives free products from brands)
- Switchback Travel (Sasha Brown): MSR Guardian Purifier review (Peru and Mongolia, three weeks of heavy daily use; last updated 14 Aug 2019)
- SectionHiker (Philip Werner): MSR Guardian Water Purifier Review (MSR supplied the unit; page dated 2 Nov 2024)
- MSR (Cascade Designs) customer reviews: Guardian Purifier (167 listed at 4.0 out of 5, 124 flagged verified buyers; all read; the maker's own Yotpo feed)
- CleverHiker (Brett Kretzer): MSR Guardian Water Filter Review (mud, sand and silt stress tests and a six-foot drop test; last updated 19 Oct 2026)