In my area grazing seems to be the biggest source of contamination. The majority of public lands here allow cows and sheep. I would not dream of drinking from any stream in these areas without boiling, filtering, or purifying.

The primitive areas are different. These are roadless areas where no grazing is allowed. I usually get my water via coffee or tea, which means it's been boiled, otherwise I carry my own. On the relatively few occasions I've taken a drink from a stream, I've had no problems. I think that the risk is a bit overblown, at least in these areas. But since I've been turned on to MP1 tablets I probably won't take even that slim chance.

Regards, Vince