just wondering how others solve the issue of filtering water below freezing?
In the past I've used the Steri-pen, chlorine dioxide tabs, boiling, or just 'hope' that the filter tubes don't freeze (lol)
but now wonder what 'technique' others find helpful
This is just one reason that I prefer to boil. After all, I am going to make coffee or tea anyway, especially when it's cool.
Bourbon won't freeze until it hits -17F, makes a wonderful coffee additive, and doesn't need to be boiled or filtered.
And I bet there are a lot of freeze-dried meals that would be better cold-soaked in bourbon than boiled in melted snow.
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In general, chemical reactions take longer in lower temps. Alcohol is germicidal, so it probably works, but lower temps may slow its actions as well. We obviously need extensive field testing.
Seriously, one thing I learned in SAR was how badly and how often alcohol can mess you up when consumed to excess outdoors, even all too often to fatality. Moderation is a different thing.
And a lot of people don't realize that, in colder weather, "to excess" can be a much smaller quantity.
It is impossible to filter frozen water so I would suggest at least heating it up to liquid form 🙂
Fresh snow is unlikely to be contaminated or contain particulates so you are probably reasonably safe just melting it if you need to save fuel and not boil the water. Snow that has been lying around for a while may be more suspect.
If you want to be sure without boiling then once you have liquid water you can use the usual methods but bear in mind that batteries may not work if it is cold, filters can become compromised if they are allowed to freeze with water in them and chemical methods may work slowly or not at all when it is cold. So you will need to do some heating to ensure the water is sufficiently warm.
Filters must be kept from freezing so the standard advice when using them in cold weather is to put it in a zip lock bag and keep them in your sleeping bag at night. During the day if it is cold enough you may also need to keep the filter close to your body or maybe insulate it and stick one of those handwarmers packets in with it separated so you don't over heat it. Some of those claim to work for up to 8 hrs. There are solid fuel, liquid fuel and electric handwarmers that possibly could be used all having their pros and cons.
I have never heard of this being done so there may be good reason not to but an interesting notion would be to flush a Sawyer water filter with some drinkable spirit like bourbon or vodka or Everclear. You would first back flush it with air by shaking and blowing to get it as dry as possible then fill it with drinkable alcohol, seal it and shake it to distribute the alcohol so it mixes with any remaining water. Probably more trouble that it's worth but could be good for daytime storage since you can drink the alcohol and it is calories but you can't eat handwarmers.
For winter use just boiling the water seems like the best approach.