The Smokys are alive with streams. The higher elevations receive, on average, 84 inches of precipitation annually. Everything grows. Rocks are covered with lichens and algae, seeds sprout on stones. At the start of these streams, high up, are springs. Their waters have been filtered through soil, gravel and stone strata until they are pure and sweet to the taste. On their way down, they may pick up chemicals arriving on polluted winds or bacteria from animals and humans and become unsafe to drink. But near the top, where the Appalachian Trail runs, I have never filtered my drinking water while backpacking. They say this is unwise but old habits die very hard and the water is so sweet.