I don’t know why there can’t be an absolute answer, or at least some answer. Either a non-working fountain used as something else is still a fountain and still falls into “A great place to be social with others”, or it’s no longer can be considered a fountain per the definition of the word “fountain” (it doesn’t discharge water) and thus no longer falls under “A great place to be social with others”. Again, I am not focused on exploration and artistic value.
If you use a bowling bag or a running shoe as a planter, they are now planters. Yes, you can clean them up, put on your running shoes and put your bowling ball into your bowling ball bag, but right now they are planters.
Several answers that I got started talking about artistic value, which made me think that people intuitively understand that non-working fountain is kinda not a fountain, and so they came to the defense of fountains using other categories.
PS My understanding is that “fountains and other water features” was included in “A great place to be social with others” because on a hot day fountains are nice to be around to cool down, and there is also an old tradition of throwing coins into fountains. I’ve never seen anyone throw coins into a non-working fountain (but I’ve seen one nomination with such fountain and trash on it), and I don’t think a non-working fountain would be a good place to sit at on a hot day. Again, I am not talking about artistic value, I am just trying to interpret what Niantic meant when they included fountains under places to socialize, and I might be wrong. I am also talking about permanently non-working, not temporary out of order.