In context of overlay "Dinge" – Brunnen zur Wasserförderung – https://osm.org/node/8342976269 via StreetComplete 63.1:

Grundwassermessstelle KP 662

Attached photo(s):
https://streetcomplete.app/p/341880.jpg
https://streetcomplete.app/p/341881.jpg
https://streetcomplete.app/p/341882.jpg
https://streetcomplete.app/p/341883.jpg