hogshead vs water tank

hogshead

noun
  • A large barrel or cask of indefinite contents, especially one containing from 100 to 140 gallons. 

  • An English measure of capacity for liquids, containing 63 wine gallons, or about 52+¹⁄₂ imperial gallons; a half pipe. 

water tank

noun
  • A tank (type of large container) used to store water. 

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