If you plan on drinking water from natural sources or melt it from snow in winter, you still need to filter or purify it before drinking it. If you’ve read someplace that you don’t need to purify water from melted snow, you are mistaken.
The problem with winter is that traditional methods of water filtration and purification don’t work very well.
- Filters freeze and can crack, completely losing their integrity.
- Chemicals such as chlorine dioxide tablets take a lot longer to work in cold water because chemical reactions work better in warmer temperatures.
- Battery operated devices like ultraviolet lights are risky to rely on because batteries lose energy much faster in cold weather, even when not in use, and shouldn’t be relied solely for survival.
Your best bet for purifying water in winter is a liquid fuel (white gas) stove. If you’re melting snow or if you’ve found a liquid source, bring it to a roiling boil for a full 3 minutes if you are above 2,000 meters in altitude (1 minute below 2000 meters) to kill all the giardia, cryptosporidum, and bacteria in it.
If you are low on fuel or trying to preserve it, bring your water up to a boil, pour it into a water bottle, and add one chlorine dioxide tablet for each liter of water. This is a good system if you use hot water bottles in your sleeping bag at night to stay warm, because the bottles will stay insulated while the chlorine dioxide is doing it’s thing. Chlorine dioxide tables, like Katadyn Micopur, which is what I use, require 60 degree (F) water to work within their published guidelines: 15 minutes to kill protozoa and bacteria, and 4 hours to kill cryptosporidium cysts. The only downside with this method is that it takes a lot of time, and is probably best done after you rehydrate at the end of the day, after boiling a liter or two of water with your stove.
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