I can't answer to all of it, but I can say that it depends on what country the person you are speaking to is from. In Mexico, it would be "el baño" or "el excuso". Probably the second one is more polite. It is probably something different in Spain, but probably "el excuso" would be polite enough and understood anywhere.

Baño = Bathroom Water = Toilet Lavabo = Sink Servicio (Higienico) = Restroom Aseo (Personal) = Hygiene (Personal Cleanliness) =)