We went to Lookout Mountain, NC and there is a trail that leads down to a waterfall, waterfall comes over a 100 foot cliff, to where we were... I walked out to that place and scooped up water and drank it, no reaction yet, but the park rangers said they wouldn't drink it, that you really don't know what's upstream, but it was probably ok.
(best water by taste test)
Years ago I was at a camp in the NC Mountains and we drank from the streams that flowed around the campsite, But this was on top of a mountain, sooo there really wasn't an "Upstream" from there...