Ice and Snow
It's imiportant to drink pleanty of water, even in frigid conditions. You can melt ice and snow for drinking water. Remember as far as pufifying, snow and ice are no purer than the water from which they come.
Dont eat either without melting. Eating ice and snow can reduce your body temperature and will lead to further dehydration. It can also lower one's core body temperature and prompt hypothermia.
Be sure any snow you use is pure white, as any hints of red or orange could indicate the presence of bacteria. If the snow is yellow, obviously don't use it.
You can use a container or a bag and allow the now and ice to melt in the sun. If boiling, which is the best option, don't fill the pot all at once. Warm a bit of regular water (or a small bit of snow) in the bottom of your pot first, and then add more some snow. When possible, always melt ice for water, it requires less heat and takes less time.