I have a question for those of you with more smarts than I have.

When did all of the waterborn critters (giardiasis for example) come into being? I drank steam water by the gallons as a kid, never got sick. I have never read/heard about the mountain men, and the pioneers in general, getting sick from drinking stream/river water, and that is all they had, unless they had dug a well. Seems to me that if critters were in the water then, and all they had to drink was that water, they would have been so sick that many would have died of dehydration. Other critters must have been pooping in the water back then, so why don't we ever hear about such illnesses from that era???