hydroelectricity vs mains

hydroelectricity

noun
  • electricity produced from the energy of moving water 

mains

noun
  • The domestic electrical power supply. 

  • The pipes of a centralized water supply that transport the water to individual buildings. 

  • The farm attached to a mansion house. 

  • The main course of a meal. 

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