mains vs water 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. 

water power

noun
  • Mechanical or electrical energy derived from running or falling water; originally obtained from a waterwheel immersed in a stream; modern hydroelectric power is obtained from turbines fed from reservoirs. 

  • Used other than figuratively or idiomatically: see water, power. 

  • A site capable of generating power or the right to use a site to generate power. 

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