I won't drink routinely from certain streams in central Colorado (tributaries of the upper Arkansas River) because I know some of the water is from abandoned mines full of heavy metals - I've seen the portals/sources. Also one hard rock mining place in Alaska that I frequent. But it wouldn't stop me in an emergency or even just when I'm really thirsty and out of water away from base camp.

OTOH, I would have to be in really dire straits to drink surface water running from ag lands here in the MidWest. It's not just the biologics; it's the ag chemicals. Don't see that need arising, but I have thought through how I would deal with the situation.

Tom