Some restaurant soups are watered down, and there’s a pun: 
 
Customer: Waiter, this soup is too weak.
Waiter: But sir, it’s our best duck soup.
Customer: Oh no it isn’t! It’s watered down!
 
“I ordered duck soup, but what I got was really watered down” was cited in a 1996 newsgroup. The restaurant pun was cited in a 1998 joke book.
 
   
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Edward A Gedeon
7/20/96
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“I ordered duck soup, but what I got was really watered down.”
 
Google Books
3650 Jokes, Puns, and Riddles
By Anne Kostick, Charles Foxgrover and Michael J. Pellowski
New York, NY: Black Dog & Leventhal Publishers, Inc.
1998
Pg. 143:
Customer: Waiter, this soup is too weak.
Waiter: But sir, it’s our best duck soup.
Customer: Oh no it isn’t! It’s watered down!
 
The Amazingly Lame Joke of the Day
Saturday, July 10, 2010
Customer: Waiter, this soup is too weak.
Waiter: But sir, it’s our best duck soup.
Customer: Oh no it isn’t! It’s watered down!
Posted by Tim Wycislak at 5:34 AM