steam power vs water power

steam power

noun
  • Power derived from water heated into steam, usually converted to motive power by a reciprocating engine (a steam engine) or turbine (a steam turbine). 

  • Means of transportation, or heavy equipment, based on such power, especially steamboats, steamships, or steam trains. 

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 steam power and water power occurred in a corpus of books? (source: Google Ngram Viewer )