body of water vs reservoir

body of water

noun
  • Any significant accumulation of water, usually covering the Earth or another planet, such as an ocean, a river, lake or a bay. 

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

reservoir

noun
  • A large natural or artificial lake used as a source of water supply. 

  • A species that acts as host to a zoonosis when it is not causing acute illness in other susceptible species. 

  • A "black box" component that receives an input signal to be read out and mapped by another process, as part of reservoir computing. 

  • A small intercellular space, often containing resin, essential oil, or some other secreted matter. 

  • A supply or source of something. 

  • A place where anything is kept in store. 

verb
  • To store or keep (something) in or as in a reservoir. 

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