Germans use generally to drink water from Mineralbrunnen (where water with a high amount of minerals come from). So there are many companies surrounding those water sources and make money. There`s no real evidence it is healthier because the body cannot absorb much of the minerals.
Water with higher minerals content is sold as sparkling water, reduced sparkling water and without any sparkling (translated silent water.. funny eh). So you can say even non sparkling water is different to tap water.
70 % of Germany drink it every day. The statistics below says water with reduced sparkling is the most bought water directly followed by sparkling water. The overall consume raised in the last 40 years from 12,5 liters to 143,6 liters, a whooping 1000%.
Since this is more a thing of religion (believe it or not) the water quality is scientifically proofed as very drinkable (tap and sold water). It is not a health risk, the controls are very strict. Some even say the tap water standards are higher than the standard of the selling companies (which is only theoretical because of the not so much tested tubes that lead to you tap).
Anyway don`t buy it, drink it from the tap!
Edit personal experiences: And yeah, I drink tap water in munich and apart from full time crazyness I´m still healthy
I wrote 'very drinkable' above because I have the experience that tap water in Germany was often much better than bottled water elsewhere. Usually drink plain water while on travels and though I was so often amazed by the countrys dishes I sometimes really wondered what they put in their bottled water.
Source: Spiegel Online - Original statistic by "Verband Deutscher Mineralbrunnen e.V."
Some more numbers: Info brochure of the "Verband Deutscher Mineralbrunnen e.V."