True, and I never liked the taste... giardia is one of the bad ones, but just read up on it a bit, be selective on where you get your back country water, it's avoidable. I once saw someone air lifted out of CO back country... giardia, diarrhea, dehydration, and that brought about... I think they called it altitude sickness.. That was my understanding at the time...
Altitude sickness - Wikipedia, the free encyclopedia