What does this idiom mean: "to be in hot water"?

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Test No. express/advan-9 "Water Expressions", question 1

Charlie's in hot water again, he forgot to lock up last night.

(a) in the bath
(b) very wet
(c) in the shower
(d) in trouble

Test No. express/advan-9 "Water Expressions", answer 1

Charlie's in trouble again, he forgot to lock up last night.

Correct answer: (d) in trouble
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what does in hot water mean?

[Torsten]

When you are in hot water you are in a very unpleasant or even dangerous situation - in other words: you are in trouble as shown in the test you are referring to.

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