And you should never drink untreated surface water, no matter how "clean" it looks: think of the "birds and the bees..." (and the fish). The birds and the bees, no problem; the fish do what they do in the water, however! Water is a very "biologically-active" medium, and when there's an entire foodchain living, loving and dying in it...you'll probably want to boil it, first.
(This is what I was referring to by the "W. C. Fields objection.")
(This is why I said "drinkable rivers" were unrealistic, Mike: all it takes is ONE cow pooping by the side of a stream, in several thousand miles of watershed, and you're at theoretical risk of e. coli. I cannot imagine of the draconian measures necessary to prevent this from happening...and you'd have to kill off all the wildlife, too, lest Bambi accomplish what Bessie was prevented from doing.)