Another option is to keep your water bottle inside your jacket and use your body heat to prevent the water from freezing. Many mountaineering jackets have internal elasticated mesh pockets for this purpose. Alternatively, I find I can just put the water bottle inside my jacket and use the waist belt of my rucksack to prevent the bottle from falling down inside the jacket. The other advantage is easy access to water without having to go to your rucksack.
- If storing the bottle within your jacket, keep in mind that this will drain body heat.
- To keep the water bottle from freezing without sacrificing body heat keep the water bottle in a 'water bottle parka'. These can be purchased at many outdoor retailers.
- You can also make these out of old "ensolite" sleeping pads by making a tube with a top and bottom.
Nalgene bottles such as this one advertises it "withstands sub-freezing to boiling temperatures". Just be sure to not fill it completely as the cap will pop and potentially split the side of the bottle if a perfectly full nalgene bottle freezes completely through.
For a good practical review of different storage vessels and their performance in freezing conditions, see this excellent article