How to Prevent your Water Filter from Freezing in Cold Weather

If you own a water filter for backpacking or camping, it’s really important to prevent it from freezing in cold weather because it can seize up or crack when it thaws. Either of these conditions are bad news because you run the risk of drinking contaminated water than can make you sick if your filter has been compromised.

One easy way to prevent water filter freeze-up is to put your filter in a plastic ziploc bag and sleep with it in your sleeping bag so that your body temperature will keep it warm. I did this last weekend when I was hiking on the Appalachian Trail in Southern Vermont and nighttime temperatures dipped into the 30’s. The plastic bag prevents any water trapped in your filter from leaking onto your sleeping bag and keeps you nice and dry.

If daytime temperatures are also below freezing then you may need to change the way you make your water safe to drink, by boiling it or by using a portable ultraviolet light called a Steripen to kill any bacteria, cysts or viruses.The only issue with a Steripen is that is less effective in turbid water with floating particulates, so you’ll need to let your water sit for a while to settle out. Chemicals such as chlorine dioxide can also be an effective in cold weather but it takes them a lot longer to kill organisms because the chemical reaction is slowed by colder temperatures.


  1. Actually chlorine dioxide is extremely effective a low temperatures, nearly as effective in the low 30's as it is at ambient temperatures.

  2. Do you mind if I ask how you know that?

    Here's an excerpt from an Environmental Protection Agency Report showing that Chlorine dioxide's effectiveness in killing cryptosporidium (cysts) decreases in cold water.

    "In a more recent study, LeChevallier et al. (1997) found that reducing the temperature from 20°C to 10°C reduced the disinfection effectiveness of chlorine dioxide on Cryptosporidium by 40 percent,

    which is similar to previous results for Giardia and viruses. Gregory et al. (1998) found that even under the most favorable conditions (i.e., at a pH of 8.5), required doses to achieve 2-log

    Cryptosporidium inactivation do not appear to be a feasible alternative, requiring doses of more than 3.0 mg/L with a 60 minute detention time. At neutral pH levels, the required doses may be more than 20 mg/L."

  3. I was just over in a backpacking forum where there was a thread of comments about the batteries in the Steripen needing to be warm to work and difficulties in freezing weather.

  4. that's good feedback. I was on the verge of buying a steripen. Were there any suggestions about viable alternatives beside boiling? Would carrying your batteries in your pocket keep them warm or would using lithium batteries which are cold resistant help?

  5. There are threads in several forums where I've read about the pen being unreliable, breaking, or having issues in the cold. Here is the most

    recent one I've run across.

  6. I meant to add – I have not tried the pen myself because of the reviews I've read and I don't like relying on something that takes batteries. I'm one of those who carries a filter and Micropur tablets for backup. Carrying the filter in the inside pocket of my jacket or between layers of shirts wouldn't be fun, but it would have to do. Fortunately I have ULA gravity filter and the size isn't unmanageable.

  7. I have the same attitude to anything the requires a battery in the backcountry: best to be avoided. My primary purification strategy is a first need filter/purifier and I also bring Micropur tables for backup in my murphy bag. I am hestitant to bring the first need on winter trips since it is big, so I might just switch to a disposible Aquamira Frontier Pro;, which can, as you say, be worn close to the body to keep it from freezing.

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