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I did a backpacking trip once where I was above treeline, there was no running water and I was low on fuel for my stove. While some of the snow was melting it was draining into the ground so fast there was no liquid water.

What I ended up doing for drinking water was throwing snow on top of a tarp and once it melted gathering the water with a bowl.

Would there be a better way of melting the snow without fire or body heat?

  • 3
    Is the temperature above or below freezing? Are you moving or camping? – James Jenkins May 21 at 15:05
  • @JamesJenkins It was above freezing, I was trying to melt it while stopped for meals. – Charlie Brumbaugh May 21 at 15:07
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If you have a clean black garbage bag with you (and if you don't, you really should :)), put the snow into the garbage bag, arrange it in a thin layer inside the bag, and lay the bag in the sun on a flat rock (if available), thin layer parallel to the flat rock. Weigh it down with a few rocks to help make contact between the black surface and the snow.

This is essentially your tarp solution, but (a) speeding things up because of the heat absorbing character of the blackness; and (b) avoiding the messiness of scooping because you need only pour. This would also work (albeit slowly) slightly below freezing, assuming sun.

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    We've always carried several. They weight almost nothing, take up almost no room, and have a multitude of uses besides the obvious one of putting your garbage in for hauling out. For example, two garbage bags keep your pack absolutely dry during even the rainiest night if you have to leave them outside the tent. Put the pack in one bag and put the second bag over the top of the pack, overlapping the first. Put a rock on top to weight the top bag down. Black, because the white bags are too small for such a use, although we carry white bags too. – ab2 May 22 at 1:15
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    They can also make a makeshift rainjacket, and can be used to wrap or store a multitude of things. In a pinch, you could even use them with tape to fix large holes in a tent or something... Yeah, I can see their survival applications :) – marcelm May 22 at 8:00
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    @ab2: Have you weighted the bags? A single bag apparently weighs about 100g which is surprisingly heavy. I also wonder if the bags are safe for drinking water (i.e. properly cleaned and a type of plastic which is safe for food/water). – Michael May 22 at 10:52
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    I think you'd at least need to be picky about the bag, some have built-in scents. But it would be trivial to combine this trick with other measures to remove that concern - put the snow in a gallon zip top bag (which are designed for food storage and 100% safe) or a drinking bottle, and then put the zip bag or bottle inside the black plastic bag in order to get the heating benefit of the black plastic. I can't think of an outdoors trip where I didn't already have both a gallon zip bag and a black plastic trash bag so this method would essentially be "free" in terms of pack space and weight. – dwizum May 22 at 15:13
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    @Michael I was skeptical about the 100g weight, so I weighed the ones I have at home; they came in at 42g/piece, which, I'll be honest, is still more than I expected. (for reference, they are these 60L bin liners, with built-in closing straps. I'd expect basic ones to be a little bit lighter) – marcelm May 22 at 15:30
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A dark coloured water bottle strapped on top of your pack would absorb quite a lot of solar heat on a sunny day. Getting the snow in would be easier with a wide neck, like a bike bottle or Nalgene. Around freezing point this can be quite effective. If you have flexible clear plastic with you in any form (a large ziplock bag for example) this can be loosely wrapped round the heat collector to act as a greenhouse. Black plastic bags can be used to wrap a clear or white bottle (tightly in a single layer).

Melting snow while moving means your meal stops are shorter, so this is with doing even if fuel is plentiful.

If you're static, a foil blanket can be used to reflect extra sunlight onto the bottle; a 3x increase in heat delivery compared to just a bottle should be easy. Insulate the bottle from the ground in this case.

Once you've got some liquid water in there it probably makes sense to top it up rather than decanting (unless of course you need it immediately). If you're planning on dissolving anything in the water (drink concentrate, soup powder etc) you may as well do so early - it's likely to increase absorption in a clear bottle.

To give an idea of the rate of melting: assume everything stays at 0°C, and you've got a 100% absorbing bike bottle (that's what I've got here to measure). At sea level in full sun that can absorb around 15W. 15W is enough to melt around 2.5 ml/min (half a teaspoonful of water). One bottle isn't enough to provide everything you need even exposed all day (and it won't be this efficient in practice), but it's a worthwhile contribution even in this very basic form. Snow is around 1/4 the density of water, so a bottle loosely filled will melt in around an hour, giving you 1/4 of a bottle of water. Pack it in tight and double all these numbers

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    If you were planning on doing this, you could carry a solar shower bladder. – Chris H May 21 at 16:47
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Possibly not-crazy idea in certain cases

If there is ice available somewhere, perhaps your tarp/bowl resulted in a convex lens-shaped extra bit of water, or you can (somehow) locate a frozen pond or even deep puddle from a previous thaw, you can consider the possibility of making an ice lens and using it to heat up something dark (your tarp or something more convenient), and using it to then melt snow.

You could heat a dark surface then put the snow on it, or put dark object on top of a layer of snow in/on something that can collect meltwater. Don't try to shine the light on the reflective snow!!

You don't need to make anything even close to an optical quality lens, you are not trying to set ants kindling on fire, just warm something at a rate well above the rate than the air is cooling it, so that it can do substantial melting.

Anything you can do to insulate the warmed material so that it doesn't lose heat to the environment rather than to melting snow is important. Anything you can do to maximize contact area of the warmed object with the snow is important.

If the sunshine is intermittent, don't add more snow than you can melt quickly. Raising snow from -20°C to zero, then watching it get cold again is a waste of sunshine.

Rate Estimation

Bright sunlight on the ground can be estimated from the 1.5 atmosphere solar standard. From data in an answer to Does sunlight warm an astronaut's face during a spacewalk?, we can estimate that there is roughly 400 W/m² in sunshine near the ground, but it varies a lot depending on time of day and other atmospheric factors. Perhaps 50% of that will get through a lens made out of water ice (dirt, bubbles, and further absorption of infrared due to water and organics) so a 30 cm diameter ice lens will deliver maybe 20 Watts. That's 20 Joules per second or 5 Calories per second.

Heat of fusion of water is 80 cal/gram, so that's roughly 4 grams of water every minute, or 240 grams/hour, or maybe 1.5 litres per day on a good day.

That really might help extend life somewhat in a pinch.

What it might look like

From http://www.primitiveways.com/fire_from_ice.html

enter image description here

From the question Has anyone ever tried to make a simple telescope using ice?:

From http://wildwoodsurvival.com/survival/fire/ice/ist.html also see Fire from Ice

enter image description here enter image description here

This is not so likely what you'll be doing, but included for completeness:

From http://wildwoodsurvival.com/survival/fire/ice/istmake.html

enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here

  • @TobySpeight thank you for the edits! I'd never seen this kind of url truncation, what's it called, how long has it been around? (e.g. [9]: //i.stack.imgur.com/6OVQZ.jpg and [10]: /a/20596) – uhoh May 23 at 21:39
  • Relative links have been around since well before RFC1738 became the standard for URLs (predating Stack Exchange by a decade or two). In fact, I'm pretty confident that they existed in the original CERN implementation before the Web went public. – Toby Speight May 24 at 8:21
  • @TobySpeight CERN isn't really relevant here. It seems that it wasn't until September 2018 that relative links started behaving properly within Stack Exchange. 1, 2. I'm curious why you convert other users' posts to relative links. What is the improvement that it brings to the post? – uhoh May 24 at 15:58
  • What makes you think that relative links were broken before last year? There's certainly been nothing wrong with them in the time I've been a member. – Toby Speight May 27 at 7:03
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    Well, the obvious improvement is a reduction in size (although, given the amount of cruft SE adds in, then the difference is small). It also contributes towards the minimum change count (although I think my rep has now reached a level where that's no longer necessary). – Toby Speight May 27 at 10:26
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Depends how much you want to melt? Battery and a heater

There are many options, but this is the first one I encountered.

https://www.aliexpress.com/item/Hot-USB-Power-Suply-Office-Tea-Coffee-Cup-Mug-Warmer-Heating-Cup-Mat-Pad-Coaster/32941949922.html?src=google&albslr=234550590

https://www.ebay.com/itm/best-DC5V-104-14cm-USB-electric-heater-pad-for-motor-car-pet-warmer-hand-glove-/391193976334?_trksid=p2349526.m4383.l4275.c10#viTabs_0

Claims it get 104F that should melt snow.

Below does 5v and 12v.

https://www.adafruit.com/product/1481?gclid=EAIaIQobChMI2urmsr6y4gIVhYWzCh2DOwxNEAkYCyABEgKZGvD_BwE

5v USB battery packs are easy to come by, which is why I picked USB.

Obviously if you get a 12v battery pack, you can heat faster and melt more.

You could also carry a small solar cell as alternate power source.

protected by Community May 24 at 12:32

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