The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with hot water
Trouble or difficulty, as in She's deep in political hot water, or We got in hot water over the car deal, or He's finally paid his tuition and is out of hot water with the school. This metaphoric term alludes to water hot enough to burn one.
[ First half of 1500s