This last trip, we climbed 4000+ feet, over alpine rocky slopes, and it was upper 70s - low 80s F - one guy had nothing but a single water bottle. Granted, we passed stream after spring after stream after spring - but he got to camp feeling awful. It was probably also elevation (10,000+ feet) but staying hydrated helps so much with that. He actually threw up and didn't eat dinner. In the morning he made up for that, eating and drinking, but I suspect he is feeling sore and playing catch up this week.

I was feeling a little dry mouthed and kept the water coming - and still drank and drank and drank water at the post-backpack pizza feed. But I was not sore, as I would have been back when I didn't mind my intake, nor was I having headache or other symptoms I used to have often. I've learned the difference between headaches - I've had migraines, cluster headache, sinus headache, dehydration headache - all of them a little different in onset and symptom presentation. All of them occur less frequently now that I have a bunch of trail nights under my belt and I have more self awareness.