Might seem like a trick question at first, but I'm serious.
When the toilet is in one room by itself (let's call this the "restroom"), and the place with the sink, washing machine, shower room and bathtub, is another room... what do you call that other room?
This is a common layout in Japanese houses and apartments, but it's not easily described in English. Because in the West the toilet and bath are together and described as a "bathroom", leading to the term "bathroom" being used loosely to label any toilet room. Which would be fine, except in the case where their actually is a room for taking a bath and washing up, but it has no toilet. So what do you call it?
Oh, and I almost forgot to mention that "shower room" describes the specific enclosed space where one takes a shower, so we can't call this larger wash space a shower room. Furthermore, "washroom" is synonymous with "bathroom", so we're back to not having a name to describe a room for only bathing and washing hands (and sometimes laundry).