Within the context of tannin extraction and mash pH, I recall a comment or two that Martin and/or Kai have made to the effect that there is a noticeable and desirable improvement when brewing tea using a favorable water chemistry (I can't remember if it was with hard water, acidified water, etc.). I can't seem to immediately dig up the thread(s) where I've seen that, but since I drink quite a bit of tea I've been wanting to experiment with that myself.