As I recently told another backpacker in a fairly untrammeled Oregon wilderness area that's at least 350 miles from any major metro area, if it were a question of getting dehydrated for lack of a filter or treatment, due to some accident or oversight, I wouldn't hesitate to drink the water there straight out of the stream, untreated, because the chance of getting a waterborne illness was extremely remote, whereas dehydration is much more immediate and life-threatening -- however, I always do bring a filter and I always use it, just because giardia is a nasty, serious disease I would not wish on anyone.