deep water deep water {n.} Serious trouble or difficulty. When Dad tried to take Mom's place for a day, he found himself in deep water. Categories: add yours {n.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: D Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Discuss