I'm fairly new to this so wanted to ask rather than make changes. Looking at this page (https://wiki.openstreetmap.org/wiki/Key:fountain) it certainly would be a splashpad.
https://wiki.openstreetmap.org/wiki/Tag:amenity%3Dfountain says the area should be encompassed.

Going by that I would think the *fountain line* should be removed as OSM complains its not a closed polygon, but I see what the original editor did by mapping the shape of the actual nozzles...