H 2 O vs rain

H 2 O

rain

verb
  • To have rain fall from the sky. 

  • To fall as or like rain. 

  • To issue (something) in large quantities. 

noun
  • Any matter moving or falling, usually through air, and especially if liquid or otherwise figuratively identifiable with raindrops. 

  • Condensed water falling from a cloud. 

  • An instance of particles or larger pieces of matter moving or falling through air. 

How often have the words H 2 O and rain occurred in a corpus of books? (source: Google Ngram Viewer )