car wash vs washwater

car wash

noun
  • An instance of washing a car, especially such a place. 

  • An event at which people (often students) wash cars, often for a small fee or donation 

  • A place at which a car is washed, usually for a fee and often mechanically by driving the car through a tunnel. 

washwater

noun
  • Water used for washing, especially in industrial processes. 

How often have the words car wash and washwater occurred in a corpus of books? (source: Google Ngram Viewer )