bowser vs water tender

bowser

noun
  • A mobile water tank deployed to distribute fresh water in emergency situations where the normal system of piped distribution has broken down or is insufficient. 

  • A buffoon or imbecile. 

  • A road vehicle (often a trailer) for the transport of liquid fuel, particularly aviation fuel at an airfield. 

  • A fuel metering/delivery pump at a filling station. 

water tender

noun
  • A specialized firefighting apparatus designed for transporting water from a water source, such as a lake or hydrant, to a fire scene. 

  • A first-class petty officer in charge in a fireroom, who supplies the boilers with water, sees that fires are properly cleaned and stoked, etc. 

How often have the words bowser and water tender occurred in a corpus of books? (source: Google Ngram Viewer )