Can You Use a Backpacking Water Filter After It’s Been Frozen?

Can You Use a Backpacking Water Filter Afters Its Been Frozen?

Most hiking and backpacking water filters must be replaced if they’ve been frozen.  When it gets too cold to keep a water filter from freezing, your best bet is to switch to chemical purification using chlorine dioxide in liquid or tablet form (Aquamira water purification drops or Katadyn chlorine dioxide tablets) or purifying your water with ultraviolet light using a Katadyn Steripen. While boiling your water will also work, it takes too much fuel to be practical unless of course, you’re melting snow at the same time and have plenty of fuel to spare. There are several notable exceptions to this rule including the MSR Guardian as well as the water purifiers from RapidPure and Grayl, which we discuss further below,

Hollow Fiber Tube Filters

The majority of backpacking water filters sold today are made using hollow fiber tube technology, including the Sawyer Squeeze, Sawyer Mini, Katadyn BeFree, the Platypus GravityWorks Filter, and the HydroBlu Versaflow. If you look inside a hollow fiber filter, you’ll see many tiny tubes packed together. Each of these hollow fibers has tiny pores in its sidewalls that let clean water pass through, but trap contaminants such as bacteria or protozoa. This style of filtering is called exclusion since contaminants are excluded from the clean stream of water that passes through the filter.

BeFree Water Filter hollow fiber filter element closeup
BeFree Water Filter hollow fiber filter element closeup

When you use a hollow fiber tube filter, some water is trapped inside the filter. When it freezes, it expands inside the hollow fiber tubes and splits them so that unfiltered water will flow through it, ruining the filter. When backpacking in cold weather, you want to keep a hollow fiber filter close to your body, so that your body heat will prevent it from freezing. I pack mine in a plastic bag and keep it in my chest pocket or sleep with it at night in my sleeping bag.

Ceramic Filters and Other Exclusion Media

A ceramic filter like the MSR Miniworks will also break when frozen because water trapped in the filter will expand, cracking the pores in the filter element. This is also true of the Katadyn Hiker Pro and the General Ecology First Need which are made with glass fiber, and the Katadyn Vario which is made with a combination of ceramics and glass fiber.

MSR Guardian

The MSR Guardian Water Purifier is the only hollow fiber-based filter that can withstand being frozen and reused after it has been completely thawed. MSR engineered the product so that it can accommodate the expansion of frozen water without destroying the hollow fiber tubes used in the filter element. This isn’t without precedent. Some companies, including Sawyer, make hollow fiber filters that are able to withstand higher water pressures (for backflushing) than the hollow fiber tubes used in other water filters. MSR has simply taken it to an extreme, which in part, explains why the MSR Guardian is so much more expensive than other water filters.

ElectroAdsorptive Purifiers

RapidPure and Grayl make purifier-grade water filters, meaning that they can remove viruses, in addition to bacteria and protozoa. Their filters use a technique called electroadsorption where relatively large filter pores are overlaid with a positively-charged mesh that latches onto germs like little magnets. The larger pore size is easier to force water through, unlike other popular hollow-fiber filters. All of their purifiers still use filter media, but their pore size is much larger, and therefore much less susceptible to damage by freezing.

Both the RapidPure and Grayl Purifiers can be used through multiple freeze/thaw cycles, although the manufacturers do recommend replacing them after they’ve been frozen twice.

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About the author

Philip Werner has hiked and backpacked over 7500 miles in the United States and the UK and written over 2500 articles as the founder of SectionHiker.com, noted for its detailed gear reviews and educational content. A devotee of New Hampshire and Maine hiking and backpacking, Philip is the 36th person to hike all 650 of the hiking trails in the White Mountain Guide. He is also the author of Backpacking the White Mountain 4000 Footers, a free online guidebook of the best backpacking trips in the White Mountains in New Hampshire and Maine. In addition, Philip volunteers as a 4 season backpacking leader for the Appalachian Mountain Club, a Long Trail Mentor for Vermont's Green Mountain Club, and a Leave No Trace Master Educator. He lives in New Hampshire.

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17 comments

  1. I don’t suppose there’s any way to tell if a hollow-tube filter has been frozen or not. I have one Sawyer Squeeze that was possibly frozen, I just am not sure. I’ve replaced it with a pump style anyway, but I hate to just toss it if it’s still performing.

    • Use it and wait 2 weeks. If you get Giardia it’s probably busted. Sorry.

      • There has to be a better way. Maybe a color dye that should get trapped by the filter? We’d need to find something that’s visible to the eye and just slightly bigger than what the filter should catch.

      • Platypus GravityWorks has a Filter Integrity Test to determine if freezing has damaged the hollow fiber filters.
        https://d1l67pfsx3wblg.cloudfront.net/pdf/GravityWorks_Ins.pdf
        A. Backflush a minimum of 1/2 L of water.
        B. Remove Clean Hose.
        C. Blow air and check.
        – Cannot blow through filter = Fiber OK.
        – See steady stream of bubbles = Fiber broken.
        STOP! REPLACE CARTRIDGE.

    • I try to force air through my dry filter, if it feels nearly impossible, I use it. It’s not scientific but I don’t like the idea of throwing out a filter every time I can’t be sure whether it froze or not. The majority of time I hike, it may be subjected to freezing temps. If you want to look up the science behind it and possibly develop a better test, Google “air testing hollow fiber filters”

  2. Have you let your MSR Guardian freeze though? I just don’t trust it for use in the winter. If the winters keep on going like they have, we’ll have running water year round, so a filter that can survive repeated freeze/thaw cycle would be ideal.

    I wish MSR could half the weight of the Guardian — I carry it for two people, but for one it’s a little too much. Its ability to filter at a fast rate out of puddles has been super useful during this drought year though, where so many water sources have been unreliable.

  3. Are there any limitations regarding water and/or air temperature that may prevent either chemical or ultraviolet light purification systems from working properly?

    • UV Light purification systems can be limited by water turbidity.

      There was a really interesting study on merely taking water, butting it into a clear water bottle and laying it in the sun. It was a group in India. The results were really good. But it took multiple hours (6 – 48 hours depending on weather) and the water had to be relatively clear (again, UV rays vs. water turbidity).

      Of course that does nothing to get rid of chemicals in the water. But neither do the hollow filter systems. The only thing that can do that would be reverse osmosis or boiling and recapturing the steam.

      Not sure that there’s any requirements for chemical treatment; but I don’t believe there are any

      For UV, if you get clear water (like found in the Sierra’s), then the UV pen should work fairly quickly. If you get it out of a river, filter it through a couple layers of a handkerchief first, then use the UV filter.

    • Not really. Chlorine dioxide just takes longer in cold water (chemical reaction – it’s about 2X) and you can’t purify ice with UV.

  4. MSR also had the MIOX purifier that produced a chemical treatment dose using bit of salt water and battery power. I have one and like it…but they don’t make it anymore. There is a newer product using the same technology the H2go, I haven’t tried that one yet. Chemical treatment might get a bad rap but it is how municipal water supplies are treated.

  5. Here’s a very interesting article about the long term use of the Sawyers.
    http://ferguskane.com/blogs/wp-content/uploads/2017/04/murray2015.pdf

    About 4 paragraphs in is a really good cleaning instruction set.

    Then there’s this document in which Sawyer refutes the ‘claims’ in the above study:
    https://sawyer.com/wp-content/uploads/2017/06/UNC-Handout_2015-10-21.pdf
    It includes analysis from a college I’ve never heard of a reviewing the process used stating some concerns of the conclusions due to that process. I agree with some of their issues, but not all.

    Please note, tthe Tufts study only tested the Sawyers because they were in Honduras and that’s what was there (Sawyer is agressive about donating these to Third Wold countries, so they will likely be the most prolific out there). But you can expect that any company using the hollow fiber filter system will experience similar results. I’m not knocking Sawyer. I’ve known of these filters since before they were commercialized through Sawyer. I own two and will continue to use them without hesitation.

    But it’s clear that further, long-term studies should be performed for this tech. I can’t find anything newer than these 2015 articles.

    After one of my trips where our water froze, I emailed Sawyer and asked. The rep said that they can’t confirm that freezing damaged the tubes, which I thought was kind of interesting. But it makes sense, since 1) I can’t confirm it froze, 2) If it did, was there enough water in there to burst the fiber, 3) It would take an electron microscope to verify and I don’t have one in my back pocket.

    Anyway, at the price of the Squeeze (or other versions/brands), you could probably call it a consumable. Use it for a couple years and if there’s even a hint that the thing is not working right, trash it and get a new one.

  6. Do you filter melted snow?
    I haven’t worried about it in the past but wondered if thar should be done.

    • Good question. You still have to purify it. Most people boil it to kill any organisms when melting snow and to heat it as hot as possible so it won’t freeze again (when stored in an insulated container). If you don’t want to do that (because it uses more fuel) you can also use a UV Steripen or chlorine dioxide.

      • When I have a question about my filter, I fill a water glass and add food dye. I then filter that water into another glass. If it is clear, the filter isn’t compromised. At least that’s my thought process.

      • That works as long as the size of your food coloring molecules are 0.1 microns or less.

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