power supply vs water power

power supply

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

  • A source of power such as the mains or a generator. 

  • That part of a piece of electronic apparatus that provides appropriate voltages for the rest of the electronics from the connected AC source. 

water power

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

  • 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. 

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

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