Whether in snow country or in the hot desert, in a survival situation, drink the water. Dehydration is pretty immediate, giardia and the like typically take a few days. Maybe in Africa, I'd rethink that advice, but here in N. America, more than likely, the water is safe, particularly melted snow.

In fact, unless there's just a lot of fuel around, you might be lessening your chances of survival by boiling the water. If you burn through all your fuel to boil the water (which takes a lot more heat than simple melting), you may not have fuel later when you need it.

There was research in the 80's that indicated that giardia was common in N American waters, but that conclusion has been refuted by subsequent research. Now, I'm not telling people to stop treating their water, but rather I'm saying, in a survival situation, drink even if you can't treat the water. I sometimes see drinking untreated water presented as a sort of life-or-death choice. "Ohmigosh, if I drink I might get super-duper-anthrax-bubonic-sclerosis and die, but if I don't drink, I'll be dehydrated and get hyper(hypo)thermia and die." I think a better assessment is: "what a fool I'd be to not drink this water that has a chance of causing some intestinal problem later and let myself get dehydrated and risk hyper(hypo) thermia now."

Based on what I've read, water taken directly from a spring is typically safe. Water taken from creeks in remote areas with no human or livestock activity upstream is typically safe. Again, I'm not calling for an end to water treatment, but untreated water isn't this death serum waiting to take to their death the weak who gave in to their thirst. I think such a scenario does exist at sea, but here on land it's not such a damned if you do, damned if you don't gamble.

Lastly, call me crazy if you will, but I drink untreated surface water in the wild on a regular basis in areas I know and am familiar with. I've been hiking since the 60's (still carry my old sierra cup). Suddenly, one day (80's) the word got passed around that all water everywhere needed to be treated. The waters of N America didn't all go bad overnight. It just doesn't work that way. I think the problem has gotten blown out of proportion, and I'm sure the water filter companies and the like haven't exactly tried to calm things down.