I would think that everyone's mineral needs are pretty much the same, so customizing them would be unnecessary. However, this could make an effective business, profitwise. There are probably plenty of health freaks that would be willing to pay needlessly high prices to get something like this.

You could make cups out of a rock that would dissolve minerals into the water that was in the cup. But it might be hard to add only a set specific amount of minerals.

Oooh good... but I HATE neadles... I think our mineral composition is the same anyway! ArtZ, I think you are of a better track, although the real answer is to drink water just for water and consume the needed minerals through natural foods and fruits and veggies. And maybe a daily vitamin for help. Sometimes the minerals don't dissolve all the way... then the water tastes funny. Or looks funny. But good thouught.