How did people who traveled out in the wild do it in the way back when before these type of things existed? Simply start up a fire and boil every single time they got a drink?
I suppose there is also an environment/heredity/ Darwin aspect to it. People who drank crappy water and lived long did so because it didn't kill them, as obvious as that sounds. Why do dogs drink crappy water with a smile on their face?
The people who drank bad water and survived had bodies that were able to process it, I guess. Those who didn't, died. We've insulated ourselves with civilization, which means a lot of people who shouldn't be alive, are. I'm not trying to be callous, but without heating and cooling and vaccinations and inspected food and treated water, a lot of people wouldn't be alive. Because they are, and they reproduce, I suppose we're producing "less sturdy" humans.
Even "sturdy humans" will kick the bucket if they get bad enough water. Refer to cholera. There was an interesting
Hell on Wheels episode on cholera, where they even kept it sorta historically accurate in that no one knew what to do, other than to try and drill for a new water source. Boiling their supply never occurred to them.