Water in Winter should be treated just like water in the Summer, because the things in water that make you sick are still there. Just like a lot of other things, they go dorment in cold and when the weather or water warms up, bingo they are there and they are alive. Can’t use a water filter in winter very well because of ice crystal forming within filter causing it to ice up and cease functioning. Best to boil water or treat with chemicals. Many small streams and springs do freeze up, but melting snow to get water is easy to do and will provide ample water. Keep water bottles turned upside down, water freezes from the top down as ice is lighter than liquid water—so if upside down and your water starts to free, you can still drink. A hydro pack within your pack and well insulated by stuff within your pack will keep your water from freezing, but water in supply tube can freeze. Carrying water bottles close to body so they stay somewhat warm will also keep them from freezing. Several hikers starting in January going northbound (Rocket, Bono, Flying Scotsman----they all have trail journals on line—read them for info regarding what you need for winter hiking. I meet two southbounders in Winter in January in Virginia—they were UK Royal Marines—tough fellows. Advantage to winter hiking, the shelters are vacant and there are very few other hikers on the trail. The AT is beautiful in Winter. Keep on hiking.
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