It is smart to be mindful of water purity when in the wild, but do keep things in perspective. When in doubt, drink!! You can always seek a cure once you have returned to civilization. Following that reasoning, I have ingested some very questionable water sources. I have never suffered any consequences.

On one occasion, two of us lived or a month, drinking water that was downstream from herds of sheep and human habitations without any kind of modern plumbing (Canuyon de Chelly, AZ). We let the water settle and then boiled it. No problems at all.

See the thread on Picacho Peak for the alternative....