Hi  These moorings are official addresses in the Dutch Registry. (Kadaster)
So please don't delete the moorings.
Removing the tag building=houseboat is possible. 
Infact it's a mooring. 
Please verify at the Kadaster if the addresses are stil in use.
Sometimes a houseboat is temporarily somewhere else.

https://bagviewer.kadaster.nl/lvbag/bag-viewer/?searchQuery=Oostenburgerkade+17&objectId=0363020003684164&theme=BRT+Achtergrond&geometry.x=123770.01613861292&geometry.y=487056.754880718&zoomlevel=14.712

Greetz,
eggie

