What is the most effective means of melting snow with body heat for drinking?

Question

The related question Is it safe to drink snow? tells us that in addtion to then normal considerations for any wild water source, you also need to consider how the snow may tip your metabolism into hypothermia

If it is cold and you are traveling and/or without a heat source, what is the best way to melt snow with your body heat to have the least chance of causing hypothermia? I think there are really two choices, put in your mouth and eat/drink it; or put in a container and hold it near your body to melt, then drink it.

Answer 1

The best way to melt snow is to put it in a bottle inside your jacket under your mid layers while you're on the move and let your body heat melt it. Do not place it against the skin, leave a layer or two between you and the bottle. It's advisable to always leave your bottle in your jacket in subzero temperatures, it can freeze if left in your bag.

Melting snow by body heat is not a fast process, so some foresight is required on your part, if your bottle is getting empty, and you don't know when you're going to find running water next, then put some snow in your bottle to replace what you're drinking. Dropping snow in liquid water will help melt it faster than trying to melt a bottle of dry snow.

Putting snow in your mouth is fine as long as you're warm, I do it all the time, but you are right that putting snow in your mouth will cool you down, so don't do it if you're already cold.

If you are borderline hypothermic, then it would be unwise to try and expend additional body heat in order to melt snow, you need to get up, get moving, and get warm before you can even try it. This will be more difficult when you are dehydrated, as hydration has a huge role in hypothermia.

One other option for melting snow is using solar radiation. Again, it's not a quick process, and you can only do it on a bright sunny day when the temperature is right. This is exactly how the survivors of the 1972 Andes flight disaster got water while they were stranded at the top of the snowy Andes mountains. They used reflective pieces of wreckage from the plane to catch the suns rays, and put small amounts of ice and snow on them then collected the drips in bottles to drink. They also ate each other... but that's another story.

Answer 2

Pee on it.

To keep the water drinkable, you'd want to have the liquids separated but still have good thermal transfer between them. A well equipped traveller will pick his/her thermos bottle and a condom, pee in the condom (ladies would probably do it the other way around), tie the condom and put in the bottle, fill the rest with snow, cap, wait and drink.

You'll curse your choice of [condom] flavour but might live another moment. If getting hypothermic, you might want to hold the filled condom inside gloves/jacket for some time before sticking in the bottle, doesn't need to be steaming hot to melt some water.

Too bad you'd probably have nothing to pee left at this situation, could try anyway.

Answer 3

Physically there are two ways for you to heat up the snow: by heat conduction and by heat radiation. Conduction means you place it somewhere close to your body. It does not matter whether this is directly in your mouth or on your belly, you will lose the same amount of energy. The only option to heat it up without losing additional energy is by radiation, i.e. placing the snow next to you outside your insulation layers. Unfortunately that will never be enough energy to melt a substantial (if even noticeable) amount of snow.

TLDR:
You do not want to waste body heat (energy) to melt snow when almost in hypothermia in any way.

If you are short of dying of dehydration and almost in hypothermia, choose the option that needs least movement and removed insulation, e.g. once getting some snow into a bottle. Get this bottle into the sleeping bag and occasionally put some of it into your mouth. Anyway, in this situation, if you are still functioning, you will probably not function rationally but on instincts...

Answer 4

Very simply: if you eat snow, all the energy that would be melt the snow is energy currently in your body. Lots of heat loss direct from your body.

If you put snow in an outer layer of your clothes, then much of the energy that would melt the snow is energy that was in the process of escaping to the outside air. Effectively the snow is capturing some of the heat that left your body already.

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To help understand this more clearly, imagine we were to wrap a person in one more very thin layer of clothing which doesn't actually trap heat, but rather measures how much thermal energy is crossing through it at every point. If the person puts the snow in a layer of clothing close to the outer layer, then it will absorb some of the energy in those outer layers. We'll see that the clothing in that area gets colder. This means that our special layer is measuring less heat crossing it near where the ice has been put because the heat flux across is proportional to the temperature difference, which is now smaller. What that means is that less heat is escaping into the air.

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Here's an extreme example to consider: The person is wearing just the right number of jackets - one more and he'd overheat. Then he puts on yet another thick jacket and waits. Eventually that outer layer is above freezing and he's overheating. He wants to stop overheating, so he puts lots of snow just inside his outer jacket. That's approximately like taking his outer jacket off, so it gets him back to normal (at least until the snow melts). If he takes that same amount of snow and puts it directly inside his inner layer, he'll end up very cold.

Answer 5

You can do exactly what you want: use your body to melt snow for drinking water without reducing your body temperature, yielding water with a negligible threat of hypothermia.

If you are prepared, then you have enough insulation available to overheat yourself, even if you are not currently using it all. If you do not have that, then you were not properly prepared for your environment. And you are asking how to use body-melted snow for water without having it make you too cold - so combine those two things!

1. Put on more insulation than you need. Heck, put it all on! Let yourself start to get hot, but not so hot that you sweat - avoid getting wet!

2. Now you need to cool yourself down. Don't do it by taking your layers off. Instead, use your excess heat to melt the snow. Put your bottle of water inside your insulation in a layer close enough to your body that it can get plenty of heat and close enough that it will cool you down faster than you are warming. If you cannot cool down fast enough and you are thirsty enough, then go ahead and melt some directly in your mouth.

3. When you are no longer thirsty and your water bottles are topped off, remove the extra insulation and start regulating your temp normally again.

The credit for this should go partly to the comment by @RussellMcMahon where he commented on another answer:

Most efficient: Add more insulation, then eat snow to maintain desired temperature. Getting too hot? Eat more snow. Had enough to drink? Reduce insulation.

You are not producing free heat from nowhere, violating entropy; rather, you are better using the heat that is on its way out of your system anyway. It is essentially a heat exchanger, which is technology used in normal household heating systems to recapture heat so that it does more work for you.

You may have a limitless amount of water for your trip doing this if it melts the water fast enough (try it before you risk your life to it), but don't forget to bring enough food!