Originally Posted by Minnewaska
As far as water from a stream, there is no way to know if it is contaminated. It doesn't take a farm upstream to do it. Ever hear of beaver fever? You can get it from the cleanest looking water. A simple backpacking water filter pump can eliminate this. In fact, you could filter water downstream from that cow farm too and very safely drink it. You test these things by putting food die in some water and it comes out clear on the other end.
I agree you can't safely drink unfiltered water from a stream, that is why I said I would never do that in my post. What I did say is that I would drink water from a spring when I know the source, meaning I have walked the length back to the ridge line. Sure, there's probably the occasional deer poop in it, but it's nothing at all like getting water from a river, and no beaver is going to build a dam on a ridge.
As for farm runoff, it isn't just the bacteria, its the fertilizer and chemicals too, filtering won't stop that.