In the break room at work, there is a tea kettle that has some unappealing discoloration. I would like to use it, and lots of people do, but I find it terribly unappealing.
I can't remove it with soap, and my fingernail has no effect. I can't even feel it, so it doesn't seem like buildup. What causes this, does it adversely affect health or water taste, and is there a way to remove it or improve this teakettle?