Read the Trinkwasserverordnung.
Trust me. Tap water is the only "food" that they check every hour/every day for the quality. You dont need to buy bottled water here.
There are even a lot of cases that they found out that the bottled water has a worse quality then the tap water. The tap water is the best here. (seriously)
It's not that we don't want to believe you, but also believe us when we say that in our region things are seriously going wrong. Really. It is even calculated that, because of the mining residue, the "salty" compounds of the ground water may rise up to more than 10 gram per liter, while the currently allowed limit for drinking water is only 250 milligram per liter. That is quite a difference! And I'm sure they will do everything to get the percentages back within range, but that also costs money. On top of this, think about what the unfiltered contaminated water does to the environment. It's really destructive, especially over a longer period of time.