Throw Cold Water On Meaning

(idiomatic, of a suggestion, idea, emotion, achievement, etc.) To belittle or dismiss; to cast doubt upon; to debunk.

Example: 1815, Jane Austen, Emma, ch. 53,
  Oh! no; there would be a Mrs. Knightley to throw cold water on every thing.—Extremely disagreeable!
1904, Edward Stratemeyer, The Rover Boys in Camp, ch. 7,
  "Now, Peleg, don't throw cold water on my enthusiasm," said Tom reproachfully.
2008, Don Walker, "Forget the wind chill. How 'bout that windfall?," Milwaukee Journal Sentinal, 14 Jan. (retrieved 8 July 2008),
  Sports economists tend to throw cold water on such studies, saying they often rely on unreliable or exaggerated data.