ablutions vs cistern

ablutions

noun
  • The location or building where the showers and basins are located. 

  • A building that houses bathing and toilet facilities on a military base. 

cistern

noun
  • A reservoir or tank for holding water, especially for catching and holding rainwater for later use. 

  • The vessel surrounding the condenser in a steam engine. 

  • In a flush toilet, the container in which the water used for flushing is held; a toilet tank. 

  • A cisterna. 

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