water main vs water pipe

water main

noun
  • The principal pipe, usually underground, for conveying water to residential and business properties. 

water pipe

noun
  • A pipe that is a conduit for water; an essential element of plumbing. 

  • A device for smoking, such as a hookah or bong, in which the smoke is drawn through a container of water before inhaling. 

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