My husband and I tasted the same tea through 8 infusions with two kinds of water:
1. NYC tap water rested for two days in a stone-ware jug (on the counter with a cover) then boiled in a metal electric kettle then poured in to a red testubin-style tea kettle a placed on a volitive.
1. Crystal Geyser bottled water. Allowed to sit for 4 hours. (don't know if spring water needs to sit) then boiled in a similar metal electric kettle then poured a black testubin-style tea kettle a placed on a volitive.
1990's Fuhai Tea Factory '7532' was the tea since we both like it.
For pots I used two similar cheap pots, though one is 10 ml larger than the other they are of the same manufacture.
My husband mixed the waters up so I would no know which kettle had which water, then I mixed the testubin-pots up so he would not know which testubin-pots had which kettle's water.
Only by sharing what we both knew could we know what water we were drinking.
The result? There was a vary clear difference. One was consistently more bitter through all infusions. The other was softer and more round through all infusions. One had a metallic aftertaste-- the other had none.
It was not enough to "ruin" the tea, but we both liked one over the other... when we decided to share which was which...it was NYC tap that won.
So, I'll stick with it for the time being.
The next test will be to see if "resting" the water even matters.