I go through about 1 to 2 liters a day depending on temp and how much hiking I have to do.
The wildcard for me is food. If I am base camped and eating normal food, I drink the above. If I am eating freeze dried or really salty prepared food, I probably bump up a solid liter a day. I don't eat a lot of sodium in my non-hunting life, and it really dries me out when I do. I also feel like I pee 4 times more often.
My pack always has some purification tabs, and a small filter (non-purifying) for use in a pinch.
Jeremy