Portland is draining another public water reservoir because some asshole appeared on video pissing in it. This also happened in 2011. Here’s a picture of the reservoir that was drained then.
If the new reservoir is like the old one, it would appear that all kinds of flying things could (and do) shit in it. The solution to pollution is dilution, so while it might gross us out to think about it, the tiny bit of birdshit that falls in the reservoir is diluted to far beyond the level of even homeopathic relevance. Is the issue that the excrement is human instead of bird? I always figured I was getting a little bit of something I’d rather not think about in my tap water, and some drunk asshole’s piss is probably less disgusting that a few other items I can imagine.