My 2 cents worth real quick.
Ever since I got my drivers license in 76 I think, I would at every chance head up into the mountains of North GA and NC and go on over night / multi-day hiking trips. Never filtered, never treated the water. Never got sick. In 79 I thru hiked the AT. Never filtered, never treated the water. Did this for 5 months. Never got sick. Continued putting the miles in into the 80's drinking lots of stream and spring water.
The Southern Appalachains are a biologically rich area. Here you have thousands of species of vertebrates and invertebrates pissing and pooping all over the land and in the water. Even the amoebas, flagellates and protozoas excrete waste. Still I gladly dipped my Sierra cup and drank and never got sick.
Then in the mid 80's the ads for water filters started showing up in Outside and Backpacker. The one with the girl coyote pissing in the stream got to me I guess, and I went out and bought a Sweetwater filter, convinced that the next sip of unfiltered mountain water would be my last. Now the romance was gone. The Sierra cup sat at home on a shelf and I now filtered into a Nalgene bottle.
I did this for a few years, and then it dawned on me - wait, Giardia has been around for millions of years most likely and I never got it before. So now I'm back to dipping and drinking on the go. Most liberating. Until a weapons grade strain of Giardia evolves I'll take my mountain water as is.
PS - I do run water with a lot of particulate in it through a paper coffee filter.
John
