Is it because toilet is commonly used to mean both the toilet itself and the room it's in? The ambiguity could be sidestepped with the phrase "communal bathroom", and I wouldn't end up picturing a dozen people sitting blithely on a giant toilet seat. :-)
Actually, in this case the distinction doesn't really exist. In general, yes, I think that would make a difference (although calling public toilets a 'bathroom' would sound weirdly American to me - not to you?). However, this particular toilet is literally just a toilet in a cupboard. It's smaller than many toilet cubicles I've been in.
Hmm. In that case maybe changing communal to unisex would be better, since it conveys the same information but doesn't have communcal's connotations of group activity. I don't know how commonly unisex is used in such a context, though.Calling public toilets a "bathroom" doesn't sound American to me, no. I'm from the west of Ireland, but I don't know if that has anything to do with it.
Mm. 'Unisex' doesn't quite seem right either because the important point is not that both sexes will be using it - we could all be female (or all male) and the point would remain. I think if I was rewriting it I'd go with 'shared' and leave it at that. To me, 'bathroom' implies a place where you can wash and have a shower and stuff. I might ask in someone's house 'where's the bathroom' without implying that I was going to have a shower, but it would be because I would expect the toilet to be in the bathroom. (And then if it was separate, I'd be scuppered.) But not public toilets. I don't know if being from the west of Ireland has anything to do with it either - I know shamefully little about the dialect there.