The best way to get drinking water is to go outside and search for Fresh Snow. This should cover the ground anywhere you can leave a foot print. Collect it and get to a Campfire. There you can drop it (the camp fire need to burn). Wait a few seconds and you will get Dirty Water (you will need an empty flask for this).
Other ways to find something to drink is to loot. Sometimes you find some:
Or you can craft and brew: