Is it pronounced Bath or Barth?
They pronounce it as ‘bah-th’. Unless you’re talking about hypercorrection by people trying to imitate a rhotic accent (e.g. the singer Marcus Mumford is sometimes guilty of this), people in the south of England don’t say ‘barth‘ and have never put an ‘r’ sound in this word. They pronounce it as ‘bah-th’.
How do British pronounce bathroom?
By metonymy, it then came to refer directly to the fixtures in such rooms. In British English, “bathroom” is a common term but is typically reserved for private rooms primarily used for bathing; a room without a bathtub or shower is more often known as a “WC”, an abbreviation for water closet, “lavatory”, or “loo”.