First, start with a good water bottle that won’t leak. Use a water bottle specifically designed to withstand both freezing and boiling temperatures. This way you can pour boiling water into your bottle without it softening and collapsing the plastic.
Use water bottles or water bladders with a very wide mouth. The wide mouth inhibits freezing at the top and freezing of the threads, so you can open the bladder to take a drink.
Start off with heated fluids and add a little salt or powdered drink mix to lower the freezing point.
During the day cover the bottle with an insulated cover designed especially for water bottles or bury it inside your pack. Leave a little space such that the water can slosh around and slow the freezing process.
At night you can repeat the steps: heat the fluid and cover the bottle with an insulated cover designed especially for water bottles. You can bury filled water bottles upside down in a snowbank when you bed down at night (don’t forget to mark the location). The snow will insulate the bottle, keeping it from freezing. Place any water you’ll be drinking during the night or in the early morning inside your sleeping bag with you. Make sure you’re using water bottles that feature several tiers of threading designed to prevent openings and leakage.
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