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How Long Should You Boil Snow in Winter?

How Long Should You Boil Snow?

If you melt snow in winter for drinking water, you still need to purify it before you can drink it. The easiest to do this is to let it boil for 1 minute if you’re below 6,562 feet (2,000 meters) of elevation or 3 minutes if you’re above 6,562 feet (2,000 meters). Boiling is the surest method to kill disease-causing organisms, including viruses, bacteria, and parasites. These are the CDC (Center for Disease Control) recommendations and I’ve always found them reliable.

Alternative Water Filtration/Purification Methods in Winter

Water filters are unreliable in winter because they can freeze, which will usually ruin the filter. They’re also difficult to keep from freezing when not in use if you’re camping outdoors in the cold. While we recommend carrying extra fuel for boiling your water, you can also use the following two methods to purify snowmelt or bring them as a backup in case your stove fails. No kidding: stoves can fail in winter. I’ve had it happen multiple times, always with canister fuel stoves.

Chlorine Dioxide Tablets

If you can’t boil snowmelt, perhaps because you’re low on fuel, you can use chlorine dioxide tablets, like Katadyn Micropur to purify liquid water. You can add a chlorine dioxide tablet (usually 1 per liter) to a water bottle as long as the water is in liquid form. Katadyn Micropur destroys viruses and bacteria in 15 min., Giardia in 30 min and Cryptosporidium in 4 hrs. If you’re not worried about “Crypto”, then adding a tablet to lukewarm water will purify it pretty quickly.

Ultraviolet Light Purification

Ultraviolet light is another viable way to purify snowmelt, using a Steripen. Ultraviolet light doesn’t add any taste to the water and is even faster than using chlorine dioxide tablets. The only real issue with a Steripen is that you need to keep the batteries warm enough to use. Some people hang a Steripen around their neck on a string, under their baselayers to keep their batteries operational.

Stoves and Stove Fuel for Snow-Melting

When it comes to melting snow and purifying it, I’ve always opted for boiling because it’s simple and I already have the stove out to do it. While you can use a canister stove for snow-melting, they operate in fairly limited weather temperature range. For example, an upright canister stove will only work down to about 15 degrees F, an inverted canister stove will work down to about 0 degrees, while a liquid fuel stove (white gas stove) will work down to -40 F.

My preference is to carry a liquid fuel stove winter stove (MSR Whisperlite) because it operates reliably in all temperatures and because boiling water for that extra minute requires more fuel. One advantage of carrying liquid fuel is that you can carry just what you need since you fill your own fuel bottles. If you carry a canister stove, you can only buy or pack your fuel in canisters, which becomes a bulky hassle when you have to carry several of them. There are other reasons to carry a liquid fuel stove in winter, but that’s a topic for another FAQ.

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  1. Interesting that you mentioned stoves failing. I camped overnight at Mt. Isolation recently and my MSR Whisperlite stove failed (due to a faulty o-ring) and because of that, we had no way to melt snow for drinking (or cooking) water that night. Needless to say, the hike out the next morning was a thirsty one! Not good.

    • Did you consider hiking down to the stream on the isolation trail or Rockey Branch to get liquid water? That would have been an option…you can usually poke through the ice.

      But regardless, it always pays to bring two of the same type of stoves with you on a trip if you’re with someone so you can share your fuel with the guy whose stove is working. I always like to carry my own stove in winter because I don’t like to wait or share. The nice thing about a whisperlite is that you can field repair it if you carry the repair kit or parts of it.

      That said, my whisperlite has never failed me, but I have had multiple canister stoves fail on trips, some in winter and some elsewhere.

      • That thought did not occur to us. The stream looked impenetrable with the ice, but perhaps we could have broken through. Ice cold stream water is better than no water, but fortunately we rationed the water we hiked in with and it all worked out.

        I thought (and hoped) that my Whisperlite would never fail either, but then again, up to that point I never did any annual maintenance/inspection either. Funning thing is, we used the same stove on a very similar overnight hike at Zeacliff the week before and it worked fine so I had no reason to suspect anything. Also, an on-site repair was really not possible at the time (without going into the details).

        I haven’t had any canisters fail on me though, but reason we brought the gas rather than the canister is because melting snow for drinking and cooking water is very fuel consuming. One canister will only barely get it done for us. Whereas, a filled fuel bottle is no problem.

        • Really. A 30 oz bottle of white gas packs up a lot smaller than 4 x 8 oz fuel canisters.
          Luckily you weren’t that far from Rt 16.
          I had a canister stove stop working a few weeks ago up in the great gulf. Luckily, I’d packed a bunch in too. But it was a thirsty morning.

    • The SVEA 123 is an alternative to the Whisperlite if you’re looking for an exceptionally reliable stove that requires zero maintenance. There’s a small (~5oz) weight penalty and it isn’t as efficient but it will never fail you. Mine is older than I am.

      • Phillip uses a picture of a Nauman campsite kitchen we built in some of his winter camping articles. I was frustrated because my Svea 123 shown there that worked perfectly in Boston at the same temperature didn’t work at 4000 feet. Be careful.

    • Nice thing about multifuel stoves is that you can use it as inverted canister stove and still bring a lightweight small upright canister stove as a backup, using same fuel (keeping the canister warm and using the water bath method, you can wrench some pressure out of a canister even with upright stove in an emergency). And unlike typical inverted canister stoves, the ones like Whisperlite Uni are designed to be field cleaned (always pack the repair & cleaning kit). I have had stoves fail in the past as well, of all types.

  2. Thanks Philip for the excellent article. Which MRS Whisperlite stove do you take on your winter hikes?

    • I take the classic, but if I were to buy a new one, I’d probably get the Universal since you can use it with white gas or canister fuel depending on the temperature and what you feel like using.

  3. I’m not sure it’s necessary to purify snowmelt unless it’s obviously contaminated.

    • That’s why I wrote this article. Maybe it’s different where you hike, but mice, beaver, deer, moose, snow hare, fox, bobcats, insects etc., and micro-organisms don’t just go to sleep in the winter.

    • Agree with B Mason. I melt snow in my mouth for a cool swallow as I hike and run. Fresh and clean-looking snow, of course.

  4. Daaaa……at least till it boils……..I think!?!?!?

  5. For winter camping, I have used for many, many years the MSR Dragonfly. It is reliable and it roars! Lately, I have been using the MSR Reactor. Yes, uses canister, but it works and it is fast!

  6. I’m curious why one would need to purify snow. Provided that one is taking surface snow from areas away from the trail and other potential sources of concentrated human activity, what is the concern for contamination? Is the idea that purification is needed supported by any actual peer reviewed scientific evidence?

    • You have obviously never seen the snow next to a popular camp spot on the likes of Pik Lenina and such :)

      Depends on your setting. Could be perfectly safe on an arctic expedition or some forgotten summit bivouac spot, not so much on popular low elevation trails where people “do sh*t in the woods”, especially since campgrounds there tend to average to the same spots all the time (due to avalanche hazards, hiking distances, established trails and such). And of course, there are countries where the risk of protozoa is much higher whenever there is people or wildlife around.

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