I absolutely consider a source of water such as that, "potable", if by, "potable", you mean clean enough to place into a pot, boil for 5 minutes or whatever is necessary to kill any parasites, and then consume after it cools. Otherwise, I consider no sources of water in the state "potable". Really, unless in an exceptionally dire situation, there is no reason to drink untreated or unfiltered water.
I have a parasite right now, and am treating it with a very nasty antibiotic called Flagyl. I feel really messed up, and have gotten worse since starting the drug. As part of my catharsis, I have read about parasites and find it deeply disturbing that estimates for infection or infestation with intestinal parasites range to as high as 80 % of the US population having it, though a-symptomatically. My symptoms started in mid to late July, with mild nausea at odd times, followed by bloating, diarrhea, the nastiest gas I have ever had, and fatigue. It came and went, but never went away. The troubling part is that if you trust the incubation time for S/S to develop after the exposure, and I have not had a latent infection or infestation for months or years, I haven't drank from water that was not out of tap since last October when I did the Romero Canyon Trail.
So, where did I get this parasite? Well, there was one exception of washing my hands in water near Hesperus Mountain in Colorado at the beginning of July, but that is not the most likely source as it was high up and there is no grazing up that high, or there is no forage for cows. Also, I didn't eat right after, but that might mean nothing. So, I think I most likely got it from eating off of a number of buffets, from a Holiday Inn Express to any of 3 Whole Foods in northern New Mexico, to some other mysterious source. I'll never know. Either way, I feel so happy to know that you can really trust our fellow man to follow what amounts to the simplest and cheapest of disease transmission prevent techniques: hand washing.
What is the significance of this? It likely did not come from a purely water source, but from a human carrier who left it on some location for me to eventually ingest. How does this affect Fossil Creek? People love to go there, our various orifices are far from clean, and anyone can deposit cysts into the water that can be ingested by you or your friends.
Nothing more enjoyable than a good hike out of town.