I drink as much as I can when I have a water source and carry as little as possible. About 75% of the time I do not treat water that I pick up while hiking. I have never had digestion distress or any other bug from back-country water. (Cavat- I do most of my backpacking off-trail) I only carry chlorine dioxide pills. I carry two 12-oz salad dressing bottles. Most the time I only fill one. PS-I probably weigh half of what some backpackers weigh. I do not tend to get thirsty (or really mind it that much) and almost have to force myself to drink water. So I think there is a lot of personal variation among backpackers. If I drink more water, it actually just makes me pee a lot and feel worse. Yes, there have been a few times that getting to a water source was a real epic. But a few times of misery is worth nearly 99% of the time carrying little water and having the weight savings.