Reading this thread for the first time I was so tempted to say the first problem with your tea is throwing it overboard........ :p
Maybe I should be ducking right about now...
even with bagged tea, taste is subjective. I know that at times some of the teabags I have steep only for a minute, others will steep as long as there is water in the cup, getting progressively stronger.
the water used is as found, one possible cause, and I would guess the chemicals in the water (obviously not salt) are the cause, but others might be length of time and temperature.
Just like coffee is meant to be 80 deg, some people can't tell, others can. Tea, to me is more a time factor - and when its less processed / natural, the time spent steeping is a larger factor. One of my friends uses a range of natural teas, and even after 5 mins, the difference between the first cup (half a shot glass) to the last cup after 20-30 mins is remarkable.