OK, so you're out in the middle of nowhere and the weather is freezing cold. Snow is piling up all around you. You know that you'll need to get a fire going, so you begin the urgent task of locating some firewood. It takes about a 1/2 hour to come up with some firewood, then you take a wad of firestarter out of your backpack and the next thing you know you've got a nice little fire going! After that, you build a makeshift water generator by setting up a tripod. The tripod is positioned close enough to the fire so that it can feel the heat, and yet far enough away so that it doesn't burn the wood. The next thing you do is, you take an old cotton tee-shirt and you stuff it with snow. The tee-shirt is dangling from the center of the tripod, which is close enough to the fire so that it melts the snow into water. Now you've got water dripping down into a plastic cup which is positioned under the tripod. You've got water, but you still aren't sure if you'll need to boil it. The snow is fresh, but you can still remember what it says in the US Army survival manual: it says that you must always purify your drinking water, even if the water was procured by melting snow and ice.

Imagine that the snow is pure and white and clean-looking and you are in dire need of drinking water. Will you be risking a serious water-borne illness if you just melt the snow and drink it ? LW.