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I was wondering if it is safe to put snow in water filtration and then just wait until it melts down if the temperature is right. Of course, carefully picked, clean looking snow.

  • Yes, though it's more common to melt snow and boil it before ingesting. – user2766 Feb 9 '15 at 16:54
  • well, if you are backcountry touring or ice climbing, carrying a jetboil along may be impractical – amphibient Feb 9 '15 at 16:57
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    It's generally safe just to scoop snow into your mouth (although it will make you cold). The belief that backcountry water needs to be treated is basically a myth: lightandmatter.com/article/hiking_water.html Since water often comes from snowmelt, clean snow is normally going to be even less likely to need treatment than running water. As noted in the question, you obviously don't want to use snow that looks dirty. I don't know whether the Chlamydomonas nivalis in pink snow is harmful or not: en.wikipedia.org/wiki/Watermelon_snow – Ben Crowell Feb 9 '15 at 20:03
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    Just make sure its not yellow – user5330 Feb 11 '15 at 23:17
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Yes. There's nothing wrong with melting snow and then purifying it with a standard water filter. Most of the water in mountain streams was snow at some point anyways.

That being said, this is generally going to be a very inefficient way to make water, and if the temperature is below (or really anywhere near) freezing, you're going to be thirsty. I would strongly recommend carrying a stove instead. Bringing water to a rolling boil kills almost all pathogens. It doesn't remove particulate matter, but clean snow generally won't have many particulates anyways.

A small stove like the MSR Pocket Rocket I have weights much less than a good water filter. Not only does it allow you to melt snow, it also allows you to get a warm drink if you need it, and you can purify regular water by boiling it too.

  • fair enough although you also have to carry a pot for boiling – amphibient Feb 9 '15 at 18:19
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    @amph I carry this small cup, an MSR pocket rocket and a 4 oz (smallest size) IsoPro canister on pretty much every ski trip and many hiking trips, even day trips. The total weight is minimal, it allows me to melt snow if necessary, and I can make hot drinks if somebody is hypothermic or we have to stay the night for some reason. They all pack together pretty small. – nhinkle Feb 9 '15 at 19:26
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    as a side note, a PocketRocket (have one too), being an upright canister stove, will start showing clear signs of weakness below -15C (even with a proper 4 season canister). That's probably when you'll need to switch to either inverted canister or even white gas stoves. (also, your cup seems awfully small to melt snow in it.) – njzk2 Feb 9 '15 at 21:37
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    @njzk2 good points. The cup is what I always carry with me, as emergency backup. For trips where I'm planning ahead expecting to melt snow (or use a stove in general) I bring a larger pot. I'm just showing that it's possible to bring those resources for a small investment in weight and space. – nhinkle Feb 9 '15 at 23:30
  • For long trips or large groups there might be some value in carrying a stove and a filter, melting (but not boiling) the snow using the stove, and then filtering the cold water. If you need to treat a lot of water, the weight savings in not needing the additional fuel to boil water might exceed the weight of the filter. – Nate Eldredge Feb 9 '15 at 23:33
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It depends on the filter. Many filters use microtubules. If there is water in the filter and the snow freezes that water then you may crack the microtubules. You'll likely have no indication that you just broke your filter, potentially leading to the consumption of contaminated water.

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    That's a good point. Although, it's worth noting that if the water is fully melted, this isn't inherently a problem. Freezing pumps can be a problem regardless of water source. – nhinkle Feb 11 '15 at 1:18
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    @nhinkle -- Agreed. I avoid filters in freezing conditions and rely on boiling. – Russell Steen Feb 11 '15 at 2:56

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