The risk is somewhat correlated with elevation, since higher elevation water is less likely to have been contaminated by humans or animals. But it is no guarantee and not something you should rely on.
Filtering water is extremely easy with products like the Sawyer Mini ($25), which you just screw to the top of a standard water bottle and drink through. It’s stupid to take the risk when the precautions are so easy and so cheap.
It is unfathomably irresponsible to let other people’s children, in your care, drink straight from the stream.
I notice marmot droppings and various birds and smaller rodents everywhere I've been in the Sierra Nevada, right up to the peak of Mt. Whitney at 14k feet even far about the tree-line. Those are all potential sources of pathogens even if there isn't human waste involved.
I am in my forties now, and I would conservatively observe that at least 20% of hikers and backpackers will choose "pure" and "pristine" streams or bodies of water as a great place to take a swim and wash the trail gunk off their feet or nethers. And I'd guess that at least 10% will casually ignore rules about where to relieve themselves and often do it far too close to trails, streams, and lakes.
People can get caught up in the romance of the wilderness and forget that countless other people enjoy those same spaces before and after your visit, even if you manage to find some place remote enough to actually be alone for a few hours or days. They assume the environment is more pristine than it actually is, and also underestimate their impact on it.
Filtering water is extremely easy with products like the Sawyer Mini ($25), which you just screw to the top of a standard water bottle and drink through. It’s stupid to take the risk when the precautions are so easy and so cheap.
It is unfathomably irresponsible to let other people’s children, in your care, drink straight from the stream.