Unable to answer "Is drinking water available here? If so, what is its source?" – Drinking Water – https://osm.org/node/597552211 via StreetComplete 57.1:

There's a fire hydrant here but no water fountain. There is a water fountain next to the public rest rooms though. I attached a photo of where the water source is supposed to be and the water fountain next to the rest rooms.

Attached photo(s):
https://westnordost.de/p/200285.jpg
https://westnordost.de/p/200286.jpg