Just because the water isn't stagnant, doesn't mean there are no bacteria or viruses (or indeed parasites like giardia or something like that)... I had to drink

Just because the water isn't stagnant, doesn't mean there are no bacteria or viruses (or indeed parasites like giardia or something like that)... I had to drink water from a raw source once and I wouldn't have done it if I wasn't reasonably sure I would be back in civilization within the next day. I kept an eye out for adverse effects; fortunately that time was okay. But now I don't leave without a life straw at the least, which I bought immediately after that trip.