If you are on welfare (Bürgergeld) all costs in Germany are covered by the state that are deemed necessary for a dignified life. Several governments over the years repeatedly tried to cut benefits below that but were stopped by our constitutional court, referencing the first article of our constitution:

(1) Die Würde des Menschen ist unantastbar. Sie zu achten und zu schützen ist Verpflichtung aller staatlichen Gewalt.

(1) Human dignity is inviolable. To respect and protect it is the duty of all state authority

It’s not a perfect system and many fall through the cracks because like everything in Germany, the welfare system is highly bureaucratic. But yes, basic necessities including tap water are covered. To be honest, I don’t get that this is so mind-blowing to some, I think that’s the bare minimum