Hi! As stated in the changeset "source" key, it was based on inspection from the ground.
Which basin are you referring to? https://www.openstreetmap.org/way/1145130593 ? If yes, then first of all, I separated the outer line & the area: this should always be done when different properties can relate either to the line or to the area. In this case, the line is the wall; and the area (which is best mapped as a multipolygon relation, even though it has only one member) is a brownfield with was:natural=water : https://www.openstreetmap.org/relation/17643073 . You can add disused:basin to it, if you wish; I haven't done that just because I didn't think of it.