hydropower vs mains

hydropower

noun
  • hydroelectric power 

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 hydropower and mains occurred in a corpus of books? (source: Google Ngram Viewer )