Boiling from snow vs. liquid water in winter

[hikerbrian]

I made this comment at the end of the MSR stoves thread, but I thought it valuable enough to get its own thread, so here it is.

In short, when collecting water for winter backpacks, your fuel will go approximately twice as far if you can find that water already in liquid form vs. melting from snow. This is because it takes a very large amount of energy to simply melt the snow, without changing its temperature (latent heat of crystallization).

You'll get your boiling water approximately twice as fast, too.

The calculations work out as follows:
If it's -13 F (-25 C) out, you need 803 KJ of energy to heat 1 Kg (=1 L liquid) snow to boiling.
On the other hand, if you can find running water at 2 C, you only need 410 KJ of energy to heat it to boiling.

I've been surprised at how often I find running water in medium and larger streams, even in the dead of winter. It really pays to harvest that liquid water instead of melting snow or ice.

 

[weatherman]

Totally. Good point for novices- bring twice as much fuel as you would in summer. Also logistically if you have a group, it often takes one person's whole attention to be the snow melter when you make camp, and if they don't have to do that, you can make camp quicker. Just don't get the water out of the stream till close to the time you'll need it if it's real cold out, or you might have yourself a potsicle before long.

 

[Tom Rankin]

It can be even worse. If the snow touches a hot pot, it can very quickly boil off, if you're not careful.

 

[iAmKrzys]

While on a subject of water at temperatures below freezing point, I have been wondering about my Sawyer Mini filter - would it loose its ability to trap bacteria and viruses if water froze (and expanded) in its capillaries?

 

[alexmtn]

While on a subject of water at temperatures below freezing point, I have been wondering about my Sawyer Mini filter - would it loose its ability to trap bacteria and viruses if water froze (and expanded) in its capillaries?

Ha! A week or so ago we covered that exact topic pretty thoroughly in the Baxter Cabin Checklist thread. The verdict is that if a Sawyer filter is wet, you need to protect it from freezing up. Sawyer isn't sure one way or the other, but are not willing to warrant that a wet filter element won't be damaged by the ice formation and open to breaches by pathogens. The only filter that came out as definitively winter proof provided you do your best to pump it clear when done using it is the Katadyn Hiker Pro.

Alex

 

[whcobbs]

Hikerbrian,
And please don't neglect springs! In Pennsylvania the springs along the AT run year round at 43 d F. With insulated water bottles, its possible to hike without melting snow, as your bottle should stay liquid for about 6 hours. However, at -16 F in the Adirondacks, this scheme failed, as no springs and Indian Creek froze solid on the way to Indian Pass.
Walt

 

[Gremlin]

What Mr. Rankin said. Please remember that it is important to have some liquid water in your pot as snow is such an efficient insulator that you can burn out the bottom of your pot before you melt any snow.