I would still be afraid of the possibility of chemical pollution within the creek. The EPA has made a lot of progress in cleaning the waterways but if someone handed me a beer made with water straight from, say, the Cuyahoga River here in N.E. Ohio (which runs just a mile from my house) he wouldn't appreciate my response. After all, it wasn't that
many years ago that the Cuyahoga caught fire.
With that said, there are a pair of videos on Youtube by Glenn who lives in, I believe, Denmark. He saw a documentary on 'how beer saved the world' and tried his own experiment. Using water from his backyard fish pond, he brewed a batch of beer. The point was to show brewing beer purified the (non-chemical polluted) water so as to be safe to drink. Back in the day, drinking beer was much safer than drinking water. His fish pond, however, was a closed system, unlike a creek where you have no idea what might have gone into that creek upstream.https://www.youtube.com/watch?v=q-SEFCOAIjc