After reading the thread about the reverse osmosis in Toronto, I felt compelled to share some of my recent experiences regarding water quality. During one of my recent travels to my friend's hometown of Xinfeng in Northern Guangdong province, I was visiting one of the local swimming spots when I saw some children drinking water from a small dribble coming from one of the rocks on the mountain. The swimming area is a small series of waterfalls rushing down the side of a mountain in such a way that it creates small, relatively deep, fresh pools of water that you can swim, dive, or relax in. We climbed up to the top of the rocks where the children were, and they said it was a natural spring and it's safe to drink the water there. Upon further investigation, by no means scientific, we found the water to be clear, clean, a little sweet, and very cold. The next day, we returned with many empty bottles of the local "spring" water and filled them directly from the source of the spring. It was very interesting to note that after you filled a bottle, the outside of the bottle had the appearance that you just took it out of the refrigerator; it was so cold and had condensation.
The tea we had available to test the water was some Autumn 04 mid grade Tie Guan Yin, high grade A Li Shan Chu Lu, and some shu-sheng 70/30 mix pu'er from a newer factory that opened in 1999; decent stuff. The water that we had beforehand was also pretty good; though, only tap water, Xinfeng's water source comes from an unpolluted reservoir and tastes like well water. When we finally got to brewing the tea (gongfu style), the first and most noticable aspect was the tea xiang wei (smell) that eminated from gaiwan. The scent was as was as if it was top grade, first pick. The Tie Guan Yin was as sweet as it was in the Autumn of last year, with full flavored freshness and excellent hui gan and kou gan. With the other teas, it was the same: It was the water that resurrected the slightly old tea.
The moral of the story, I suppose, would be find the best quality water that you can possibly find; tap water simply WILL NOT do. Also, go climbing mountains to find water if you can!