water level vs watermark

water level

noun
  • The level of the water table below ground. 

  • Of a route that follows a riverbank or shoreline. 

  • The waterline of a ship. 

  • An instrument to show the level by means of the surface of water in a trough, or in upright tubes connected by a pipe. 

  • The level of a body of water, especially when measured above a datum line. 

watermark

noun
  • A mark indicating the level to which water has risen. 

  • A translucent design impressed on the surface of paper and visible when the paper is held to the light. 

  • A logo superimposed on a digital image, a television broadcast, etc. 

  • A value stored in a datafile to ensure its integrity, so that if the file's contents are changed then the watermark will no longer match the contents. 

verb
  • To mark paper with a watermark. 

  • To mark a datafile with a digital watermark. 

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