Thanks I missed that it was already there - and so did probably arepo when he wrote the note.
So I guess the note could be closed except for the question of the water quality.
Unfortunately there seems not be a value for tagging it as drinkable after treatment.
https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwater_well
https://wiki.openstreetmap.org/wiki/Key:drinking_water