Has anyone ever used hand crafted iron water kettles? They are not coated on the inside and deposit minerals in the water. They've been used in Japan for generations. You usually see a traditional version(kama) in tea ceremonies. They are like the yixing pots of water kettles.
Also on the flouride note, green tea does have it. Matcha has a concentraded version of it and it is said that in the past they recommended rinsing your mouth with it to protect your teeth.
Oxygen in water. If you overboil your water it does eliminate the amount of h20 but can't you put some back in by doing water transfers from one container to the other?