Guest - Not logged in 

Reviews > Water Treatment > Filters > MSR Hyperflow Filter > Test Report by Rick Dreher

MSR HyperFlow Microfilter
Test Series by: Rick Dreher

INITIAL REPORT - March 15, 2009
FIELD REPORT - May 31, 2009
LONG TERM REPORT - July 25, 2009


NAME: Rick Dreher
EMAIL: redbike64(at)hotmail(dot)com
AGE: 55
LOCATION: Northern California
HEIGHT: 6' 0" (2.10 m)
WEIGHT: 175 lb (79.40 kg)
TORSO LENGTH 20 inches (50 cm)

I enjoy going high and light, and frequently take shorter "fast- packing" trips. My longest trips are a week or so. I've lightened my pack load because I enjoy hiking more when toting less, I can go farther and over tougher terrain, and I have cranky ankles. I use trekking poles and generally hike solo or tandem. I've backpacked all over the U.S. West and now primarily hike California's Sierra Nevada. My favorite trips are alpine and include off-trail travel and sleeping in high places. When winter arrives, I head back for snowshoe outings in the white stuff.


Product Information & Specifications


Maker: Mountain Safety Research (MSR)
Web site:
MSRP: $100; replacement filter cartridge: $40
Year of Manufacture: 2009 (cartridge dated 12 2008)

Weight, spec: 7.4 oz/209 g
Weight, measured (total, incl. storage sack): 9.4 oz/266 g
Weight, measured (minimum--pump, hose, prefilter): 7.4 oz/210 g
Weight, measured (filter cartridge only): 0.8 oz/23 g
Dimensions, spec: 7 x 3.5 in./17.8 x 8.3 cm
Dimensions, measured (pump only): 7 x 2.5 in./18 x 6 cm
Claimed performance: 3 liters per minute flow rate, 1,000 liters cartridge life
Claimed Maximum Filter Pore Size: 0.2 micron (µm)
Filter Type: Microfilter (intended to remove bacteria and cysts)

Includes: HyperFlow pump filter unit, Quick Connect bottle adapter, Clean Side cover, inlet hose, prefilter, instructions, filter test guide, storage sack with quick reference guide.

Initial Impressions

Complete package: filter, prefilter, hose, adapter & bag


The HyperFlow is truly small compared to my older pump-type water filers, and unlike those is small enough to warrant packing on day hikes. The specified pumping rate is quite high compared to those same older, larger pumps--a second advance.

The felt-tip-marker-sized filter cartridge is integrated into the pump piston itself, which is the secret of the HyperFlow's diminutive size. The filter medium is described as a "hollow fiber membrane-HFM," a bundle of fibrous tubes that provide a lot of filter media surface area in a small package, particularly compared to typical pleated fabric cartridges. I liken it to a fistful of folded drinking straws, except these straws are very small and porous. Water is forced under pressure through the straw walls from the outside, discharging through the open ends and leaving contaminants on the outside walls. (MSR has further information about the filter technology on their Web site, beyond the documentation provided with the HyperFlow.)

Filter cartridge discharge side closeup.

MSR put a good deal of effort into preventing cross-contamination between source water and discharge (clean) water. The discharge port has a protective "Cleanside Cover" for capping it between uses. The bottle adapter has a similar cap to cover the inlet, and is also provided a separate pocket in the storage bag. These measures minimize the possibility of the possibly contaminated inlet hose and prefilter coming into direct contact with the pump outlet or bottle adapter. They also fend off stray water and dirt.

Materials, Fit and Finish

The filter body is rather similar to a compact mountain bike tire pump. It's made of sturdy translucent red plastic with black rubber grips molded into the head and body. The end of the pump cylinder houses the inlet hose port and the large check valve, and I'll typically hold this with my left hand. Opposite, at the end of the piston is the discharge port. The piston assembly comprises a handle, the filter cartridge (which is also the piston shaft), the small check valve, the piston and the pump seal (o-ring). I'll normally operate the piston with my right hand.

Even smaller than a mini bike pump.

Setup and Use

Out of the box, various bits require simple assembly: attach the hose to the prefilter and pump inlet port. Once assembled, the hose can be left in place and wrapped around the pump, secured by hook-and-loop straps permanently attached to the prefilter.

To use, place the prefilter face-down in the water, attach the collection container, and pump. Here again, the bicycle pump analogy comes into play, as pumping is a two-handed push-pull process. The pulling action draws water into the piston and the push forces water through the filter and out the discharge port.

There are three ways to attach a collection container: via the Quick-Connect cap threaded into a standard 39 mm-opening vessel (e.g., standard widemouth Nalgene bottle); via the pump outlet inserted into a narrow-mouth container (such as a standard commercial drinking water bottle or narrow-mouth Platypus container); or via a hose, such as a hydration system drinking hose. Of course, the pump outlet can simply be aimed into an open vessel, such as a cookpot.

The prefilter is buoyant, and is placed facedown on the source water at or just below the surface. Water is drawn through the mesh and into the inlet hose. Note: other prefilters can be substituted for the supplied unit. A more aggressive prefilter might be warranted with very turbid source water, as the HyperFlow's mesh is coarse enough to pass fine silt. MSR advises allowing cloudy water to settle in a container before filtering, and only using the top part of the water itself.

Once pumping is complete, the directions recommend first discharging excess water by pumping air through the filter. This is in direct contrast with the warning to let no air in during backflushing (see below). Then, remove and stow the Quick-Connect cap in its protected side of the carry bag, replace the Cleanside cover, wrap the hose around the unit and strap in place, and stow the works in the mesh side of the carry bag.

Backflushing and Maintenance

Specifically because of the unique filter medium, the directions specify routine backflushing in the field for every 8 liters (2 gallons) pumped. Backflushing is intended to dislodge and discharge the filtered debris and return the filter element to full capacity. The process is a little involved, requiring disassembly, reversing the two check valves, reassembly, pumping a half liter of clean (filtered) water (ten pump strokes) backwards through the filter via the outlet port, a second disassembly, returning the check valves to their normal operating position, and reassembly. Users are cautioned to carefully avoid pumping any air during backflushing; doing so evidently can cause an airlock and greatly reduce flow rates through the filter, perhaps permanently. So adamant is MSR about this they print the caution in bold, italic, all caps.

Other than the no-air dictate, my biggest takeaway from the backflush instructions: make sure both check valves are pointed in the intended water flow direction.

HyperFlow users will become quite familiar with the bits.

Other Precautions

MSR warns against letting the filter cartridge freeze or dropping it. Freezing evidently damages the filter tubes and it's not hard to imagine expanding ice cracking the casing itself. MSR describes how to test for damage by seeing whether the unit can hold a vacuum. Because the HyperFlow is small, it's not unreasonable to take it into the tent or even stow it in a pocket on really cold nights. For that matter, the vulnerable cartridge itself could be removed and kept warm, and hardly noticed.

Longterm Storage

MSR recommends running a liter of water with two drops of household bleach through the HyperFlow before extended storage (two weeks or longer) and after longer use (15+ days) to prevent algae growth from clogging it. They warn that higher bleach levels can damage the filter. My standard filter storage procedure is to clean and dry everything, allow the filter cartridge to dry thoroughly and store it separately to maximize airflow. One of my initial questions was whether the HyperFlow's cartridge can actually be dried completely. (Answered below.)

Return of Mr. Yuk to the cartridge's inlet side.


MSR sells replacement filter cartridges ($40) and a maintenance kit ($20), which contains the most obvious parts subject to wear--the o-rings and the check valves--as well as silicone o-ring grease and repair tools. I wouldn't mind being able to buy the piston o-ring separately, as it's clearly the part most subject to wear. They also sell a gravity kit ($50), which is a raw water reservoir that allows the filter to be used without pumping. The prefilter and Quick-Connect cap are sold individually, and could be used with numerous other filter systems.

The Instructions

"Clean water" in nine languages.

The HyperFlow comes with three sets of instructions: a main instruction pamphlet (the box held nine copies, each in a different language); a filter test guide; and field operation and backflush instructions sewn into the storage sack. The well-illustrated main pamphlet covers most aspects of filter setup, operation, field maintenance, cleaning and disinfection, storage, troubleshooting and repair. Poring over the exploded diagram was very handy in sorting through questions I had. The manual folds small enough to reasonably be carried on the trail, if so desired. Not a bad idea during the learning curve. If lost, a pdf of the instructions is available on the MSR Web site.

The filter test pamphlet details how to test the filter integrity should damage be suspected. The backflush instructions are a field guide to tackling this evidently important routine field task, which requires some disassembly.

Trying it Out

The pump is very comfortable to hold and the black rubber grips are easy to hold with wet hands. I especially like that the transparent plastic helps me see and purge air bubbles.

Once I got the hang of aligning the locking notches, unscrewing the housing to access the check valves is pretty easy. The valves themselves basically fall out (don't disassemble perched above a roaring stream!) and are easy to reverse for backflushing and subsequent reassembly. They're color-coded black and red to further differentiate small and large. To make routine maintenance like backflushing something a tired hiker will even consider, the process needs to be both easy and as foolproof as possible.

At first I thought the filter cartridge was permanently mounted into the pump handle and discharge adapter, but a closer look at the instruction's exploded diagram assured me it's threaded on both ends. On my sample the cartridge was screwed into the handle TIGHT but it did come out, so I could weight it and get a better look at the filter medium. At 0.8 ounce (23 g) it's amazingly light and small, which is good news for anybody considering toting a spare.

I tried the three connection methods: Quick Connect cap, hose, plug into standard water bottle. All seem to work fine, although it can be interesting wrangling a large container hooked rigidly to the outlet while simultaneously pumping. I suspect the hose connection will prove easiest. A bit of output hose stored on the clean side of the bag might be worth toting.


I tested the HyperFlow's initial pumping rate in the best circumstances I could cobble together. I pumped clean water from a full sink into a container for a minute, then measured the total water pumped. In my test total water pumped was about 2.25 L (2.4 quarts) in 42 complete (in+out) strokes. The MSR spec is 3L in 80 strokes, and I take the stroke count spec to be counting each direction. My total volume was somewhat below spec, but nevertheless lot of water compared to other filters I've used. Two compete strokes primed the pump and got water flowing, and the pumping action was firm and smooth. The prefilter had a tendency to flip over and pull in air, slowing the process a bit.

I then backflushed the HyperFlow, following the initially complicated-seeming directions. In practice it proved pretty easy, at least at home in a sink. My main concern, after reversing the check valves, was to not pump air, as MSR cautions. Keeping the outlet (now, inlet) port underwater and pumping fairly slowly provided a steady flow, and ten "full" pump strokes were done pretty quickly.

After my backflush test I disassembled the filter to re-reverse the valves and shake out stray water. After shaking as much water as I easily could from the filter cartridge I weighed it to see how much water weight it might have gained compared to dry. My scale showed it weighing the same as when new, so the residual moisture can't have been more than a couple grams.


Bundled & ready to go.

My test approach is simple: use the HyperFlow this spring and summer on all my hikes, be they overnight or for the day. I'll follow the maintenance schedule and occasionally test the pump rate to see whether the filter can maintain what it could do on day one.


On initial review and use, the HyperFlow mostly lives up to its aggressive specifications. It's small and light, fairly easy to use and pumps water very quickly--just not quite at a 3 L/min clip. The recommend periodic backflushing appears to be not a terrible inconvenience, and should hopefully maintain this high pumping rate, as well as extend the life of the $40 cartridge.

I'm very pleased with the easy setup and storage and the efforts to eliminate cross-contamination, without which the whole filtering exercise can easily be made moot. I'm also happy with the small size and weight of replacement filter cartridges and the fact that they can be completely dried out for long-term storage (answering an earlier question).


Especially considering the frequency of disassembly for backflushing, I'd like to see o-ring lube included with the HyperFlow.


I sincerely thank MSR and for the opportunity to test the HyperFlow Microfilter!


Field Locations and Conditions

In camp.

I've taken the HyperFlow on cold-weather and mild-weather trips into the Tahoe Sierra Nevada and the Sierra foothills, totaling three day hikes and three overnights. The weather range has been broad, with daytime temperatures in the 30s F (2 C) to perhaps as high as 70 F (21 C) and lows down to 20 F (-7 C). The overnight lows are my main concern because I have to heed MSR's warnings about not freezing the filter (more below). Altitudes have ranged from 2,500 to 7,500 feet (750-2,300 m).

Water temperatures, while not measured directly have been from near-freezing snowmelt to much warmer, perhaps mid-50s F (13 C). This too has proved important. More observations on air and water temperature are presented below.

I don't know how much water I've pumped in total, probably 20 or 30 gallons (80-120 L). (It's hard to keep track.) I've backflushed it perhaps six or seven times, more out of following the instructions than to restore flow. Backflushing isn't difficult but it's a chore I seem to put off, especially when it's cold and I don't want to fiddle with the filter bits with my cold, wet hands. Fingerless grippy-palmed gloves are great for assembling and operating the filter from a creekside snowbank.

Field Performance

Prefilter in flip mode in near freezing water.


Because the HyperFlow is relatively small I can stow it in an outside pocket of some packs, easy to access on the go and unlikely to get anything else wet. It goes in the main pack compartment when I'm hiking below freezing. Easy access and use means I can take less water on the trail because I can easily resupply while hiking. Not every pack has big exterior pockets, and then the filter has to go inside and I tend to skip the refill on the go. As summer hits with high temperatures and dry streams, easy filter access is less important.


So far I've used streams, creeks, lakes and irrigation canals as water sources. The creeks and canals have all had strong flow, since it's runoff season. The water has mostly been visibly clear, but with runoff silt and discoloration showing in some of the larger creeks. The filtered output water is clear, sometimes showing a faint color tint (expected with a non-charcoal filter such as this). The HyperFlow lends no taste to the water that I've been able to detect.


Connecting it directly to a container—water bottle or soft-sided vessel—makes the HyperFlow a bit of a handful, as I have to control both it and the container while pumping and while minding the pickup hose. On the trail I typically either use supermarket drinking water bottles connected directly to the outlet or plug in my drinking water bladder hose after disconnecting the bite valve. The valve comes off some brands easily, only after a massive struggle with others. In camp I rely on a large Nalgene Cantene. I connect to that using the HyperFlow's screw-on Quick Connect cap.

Typical "free" water bottle fillup.

Controlling this rig while filling took some practice, and a decently flat, wide workspace by the water source really helps. The prefilter, which I've come to think of as a tiny manta ray, doesn't like to stay beneath the surface in flowing water and also has an uncanny desire to flip over, with the entry port facing upward. This means I'm spending time coaxing it back under the surface; otherwise, it pulls a lot of air into the water stream. I've learned to anchor the prefilter with rocks to stop if from surfacing. I try to aim it towards clear water to not ingest debris. The pump primes and delivers water with just a couple of strokes, so it begins filling my container right away once I'm set up.

Water Temperature

I've found cold water affects flow, and the reason is air. In my early trips I'd get a lot of air mixed with the water while pumping, and I determined it was not being pulled through the hose (once I decided to sink the prefilter). If I pumped fairly fast, a good deal of air would be drawn inside the pump, and appeared to be pulled past the piston seal (o-ring). The airflow is visible through the clear pump cylinder.

More recently with warmer source water the problem has abated, so my hunch is very cold water shrinks or hardens the o-ring, affecting the seal against the cylinder wall. Additional o-ring lube doesn't have an effect (at least the lubes I tried). The result is reduced pumping rate by perhaps 50% to avoid pushing air into my container, as well as trying to avoid any possibility of forcing air through the cartridge. As noted, warmer water has basically eliminated the problem.

Air Temperature

Since I've camped well below freezing (about 20 degrees F/-7 C) I've heeded the caution to not let the HyperFlow freeze. My solution is to place it in my pillow bag along my spare clothing. This system works just fine—I don't notice it there and it doesn't freeze. In freezing mornings I keep it in a jacket pocket until it warms up and I can stow it for the day. I could foresee this being an issue in extended cold conditions. Would I have to always keep it on my person to keep it from freezing? Of course, at some point in winter it makes more sense to melt snow than filter or treat water, regardless of what filter I might have.

Additional Web Support

Since my initial review MSR has posted three brief videos demonstrating filter use, backflushing and testing filter integrity. They're a welcome simplification and addition to the printed manual. In a palm-to-forehead moment I also learned the trick of stowing the Cleanside Cover on the Quick Connect adapter when off the filter. Why didn't I think of that?

Down and Out for Now

After my last trip I rinsed out and backflushed the filter at home. After backflushing I took it apart to realign the check valves and allow the cartridge to completely dry, and noticed a segment of one of the ridges that traps the discharge end o-ring seal has cracked and split. This leaves the o-ring only partly supported. I can't guess why this damage occurred, unless perhaps it was weakened by the very tight torque that had been applied to the threaded connection when the filter had been built. But if that's the case, why would the ring away from the threading crack, and not the close one?

To be clear, this break occurred at the cartridge end that threads into the discharge port and as such, isn't under significant pressure except when backflushing. The sliding pump seal o-ring and the inlet end o-ring are undamaged.

Regardless of the break's cause, I don't consider the filter usable with this damage and emailed MSR customer service describing the problem and asking whether repair was possible. The next working day I received a reply with an RMA number and an invitation to ship it to them. Once I made the following photograph showing the damage, I shipped the filter to Seattle.

Surprise breakage.


The HyperFlow has performed well and supplied all the water I required, when I wanted it. The introduction of air into the flow with very cold water slows it down, but it still works. Water flow is a good deal faster when the water is warmer (and not swimming-pool warm either). A second annoyance is the prefilter's surface-and-flip habit. Of course, the HyperFlow is still small and light and compact and a solid performer, volume-wise.

Clearly, the damaged filter cartridge is unexpected and puts a damper on my test, but it also gives me a chance to work with MSR's customer service. I have backup water treatment in the meantime, so I won't be sitting home watching the mail.

Further Suggestions

I think a length of discharge hose would make a great addition to the Hyperflow. I also suggest MSR take a look at the piston o-ring material with respect to improving the seal at water temperatures near freezing.

Please check back for the long term report in about two months. Drama!


Long-Term Test Locations and Conditions

During this report period I've taken the HyperFlow on three multi-night trips and two day hikes. The camping trips were to Lassen National Park (three nights) in the southern Cascades and two backpack trips into the Tahoe Sierra, in Desolation Wilderness (one night) and in Tahoe National Forest (two nights). The day hikes were also in the Tahoe Sierra. Air temperatures ranged from about 40 F to over 90 F (6-32 C) and I'll estimate water temperature ranged from 40 F to 60 F (6-15 C). Altitudes ranged from 5,500 to 10,000 feet (1,700-3,050 m).

Performance in the Field


When last we heard from out test team (me) in the field report, the test HyperFlow had been sent to MSR Customer Service after they issued an RMA number via email. Two weeks later I received the original filter back along with a new cartridge, an invoice indicating the replacement was at no charge and a repair tag bearing the word "overtorqued." So it appears the difficulty I had the first time I unscrewed the cartridge from the filter's discharge end was due to overtightening on assembly. My conclusion is the excess force transferred from the outer support ring first to the o-ring and on to the failing inner support ring. Why it took awhile to show will remain a mystery, but a crack expanding over time seems probable.

Whatever the problem source might have been, the MSR customer service I received with timely and completely satisfying. Since I did not identify myself as a tester it was handled through the same channels as any customer.

I reassembled the filter (after lightly lubing the o-rings) and it was back to like-new condition and performance.


Fitted with the new cartridge, the HyperFlow delivered water in a steady, high-flow manner throughout the long-term period. Presuming a 4 liter/day average, I ran about 44 L (11+ gallons) through the filter. I backflushed it after each trip and once in the field. Backflush pump resistance seems higher now, perhaps due to the undamaged cartridge, and the filtering flow rate has been consistently high.

I filtered from small streams, large, fast creeks and lakeshores. I focused on finding very clear or moderately clear sources to minimize how much particulates I would uptake. Likely because of good sources, flow rate remained consistent. I also figured how to keep the floating intake below the surface: I put a stone in a mesh prefilter bag, attach it to the hose near the intake and sink the works into the water. This works great and means I don't have to pay any attention to the intake or corral the hose while pumping. The mesh bag weighs a scant few grams, and is now a permanent part of my HyperFlow kit.

Rock-in-mesh-bag anchor keeps intake underwater.

I continued to fill Nalgene Cantenes (soft-sided containers), supermarket drinking water bottles and wide-mouth bottles using either the screw cap or plugging the narrow-neck bottles into the discharge port. I also found a hydration bladder and drinking tube with an easily removable valve that I can take off and plug into the HyperFlow discharge. This is a great way to refill on the trail because I don't even have to remove the bladder from my backpack. A lot of packs stow the bladder in low inside pockets that require me to half unpack to retrieve the bladder to fill it. This method completely avoids that hassle. In fact, with some packs I can do this without even taking it off because I can easily retrieve the filter from the side pocket while still wearing the pack. This is a very nice capability.

Intake under control.

Once back home I disassemble and rinse and dry everything after backflushing, and when done stow the cartridge separately from the pump so it can completely dry between trips.


I really like the HyperFlow. It performs better than other filters I own while being lighter and more compact. It's faster to assemble and use, meaning I can get pumping sooner and finish gathering water more quickly. The flow rate is greater. There are more techniques to learn and perfect with the HyperFlow compared to my other pumps, but once learned they seem pretty straightforward. The literature is pretty thorough, but the on-line videos are a must-watch to really understand key techniques and to learn some good tricks not covered in the literature.

The broken cartridge was unfortunate and a strong incentive to carry a $40 spare (costly, but small and light). MSR customer service was excellent and snapped me out of my grumpy mood from not having a working filter for a few weeks. I'm hoping, of course, that the broken cartridge was a one-time event.

I don't feel as though I've had the equivalent of a full-season test due to swapping the cartridge halfway though—effectively "resetting the meter" on cartridge life. I'm curious as to its life over the long haul, especially with respect to the point at which backpressure can no longer be corrected with backflushing. On the other hand, I did use the works quite a bit with both cartridges and can report no wear-and-tear issues whatsoever, either with the plastic body or the various o-rings. The prefilter is not subject to permanent clogging because it is easily cleaned between uses.


I don't have any major design changes to suggest; the HyperFlow is a well thought-out product. If I were to focus on anything, it would be modification of the prefilter to force it to remain face-down in the water. In the meantime I'm happy with my resolution of weighting it down. My other suggestions are to supply a discharge hose and o-ring grease with the HyperFlow.

Fill that reservoir still inside the pack!

Future Use

The HyperFlow is now my favorite pump filter. It will share my permanent water treatment rotation with the UV Aquastar, a Safe Water Anywhere filter bottle and chlorine dioxide tablets. I'm pleased with this option set, which gives me plenty of choices to match a wide array of trips and conditions.


My sincere thanks to MSR and for the opportunity to test the HyperFlow.

This report was created with the Report Writer Version 1.5 Copyright 2009. All rights reserved.

Read more reviews of MSR gear
Read more gear reviews by Rick Dreher

Reviews > Water Treatment > Filters > MSR Hyperflow Filter > Test Report by Rick Dreher

Product tested and reviewed in each Formal Test Report has been provided free of charge by the manufacturer to Upon completion of the Test Series the writer is permitted to keep the product. Owner Reviews are based on product owned by the reviewer personally unless otherwise noted.

If you are an avid backpacker, we are always looking for enthusiastic, quality reviewers. Apply here to be a gear tester.

All material on this site is the exclusive property of
BackpackGearTest software copyright David Anderson