My other experiment: 'designing' water.
Most filters remove impuriteas from your tap water and reduce the dissolved solids slightly, but not much. They are not effective at all in turning hard tap water into soft tea water.
So I just got a 'Zero Water' filter to play with. It is very slow, but effective at removing all solids from water. Really reads 0 TDS.
Towards the design bit, I am mixing in water from a Pur filter until TDS reads around 40. (Matches the current standard, Poland Spring).
By itself, my water doesn't taste as good as the PS yet, but it is making pretty decent tea, much better than normal filtered tap. The 0 TDS water for regular drinking tastes better than the mix, I might try a different brand of filter, or Concentrace, for bringing up the TDS.
In earlier experiments I think Concentrace gives a very artificial taste at a very low concentration (few tiny drops).
I have also tested a Mavea filter recently, it also makes very good water but is too soft / low in minerals for many teas.