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.
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.
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.
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.
- Grayl Geopress Purifier Bottle
- Grayl Ultralight Purifier Bottle
- RapidPure Intrepid Bottle Purifier
- RapidPure TrailBlazer Gravity Purifier System
- RapidPure Scout Inline Hydration Pack Purifier
- RapidPure Universal Bottle Purifier Adapter
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.
- Ultraviolet Water Purification 101
- Cold Weather Water Treatment and Purification
- How Much Water Do You Need for Day hiking?
- How to Prevent your Water Filter from Freezing in Cold Weather
- Hiking and Backpacking Hydration Systems: Pros and Cons