Thanks for pointing out "water_source". There are indeed a number of fountains in Zurich that would need to be changed. However, this is actually not an on-site observable fountain characteristic... for this reason, the information is more suitable on wikidata.
We have proposed a corresponding property but it hasn't been accepted yet... votes and contributions are welcome! https://www.wikidata.org/wiki/Wikidata:Property_proposal/type_of_water