To be in hot water means to be in trouble because of something you've done. When your teacher catches you passing notes during a quiz, you're in hot water. When you accidentally break your neighbor's window playing baseball, you know you're in hot water the moment you hear the glass shatter.

The phrase captures that uncomfortable, anxious feeling of knowing you're about to face consequences. You might tell a friend, “I'm in hot water with my parents” after coming home an hour past curfew, or say, “We're in hot water now” when your group project partner discovers you forgot to do your part.

The expression probably comes from the very real discomfort of being in water that's too hot. Just as you'd want to get out of a scalding bath quickly, being in hot water makes you want to fix the situation as fast as possible.

Notice that being in hot water usually means you did something wrong yourself, even if it was an accident. It's different from simply having bad luck. And while the trouble might feel terrible in the moment, most hot water situations eventually cool down once you've apologized, fixed what you broke, or accepted the consequences.