problem vs deep water

problem and deep water both are nouns.

Word	Noun	Adjective	Verb	Adverb
problem	Yes	No	No	No
deep water	Yes	No	No	No

As nouns, deep water is a hyponym of problem; that is, deep water is a word with a more specific, narrower meaning than problem:

Other hyponyms of problem include pressure point, can of worms, growing pains, hydra, matter.

problem (noun)	deep water (noun)
a source of difficulty	serious trouble
a question raised for consideration or solution
a state of difficulty that needs to be resolved