When a person says he is in hot water, this typically means he's in some sort of trouble. For example, a child who failed his test or got caught skipping classes may say he's in hot water because he is likely to be reprimanded or punished by his parents. An adult can also be in hot water for any number of reasons, ranging from forgetting to call his wife when he would be late for dinner to getting too many speeding tickets. When used this way, the phrase "hot water" is not meant literally. Instead, it is a figurative statement that is referred to as an idiom.
Often people use creative ways to say that something is wrong and they are in some type of trouble. One of these creative ways is by saying they are in hot water. This doesn't literally mean the speaker is in heated water or any type of water at all. Instead, this phrase is an idiom that is used to creatively and figuratively indicate that the speaker is in trouble. Usually, people use this phrase with others from the same region who are likely to understand what it means without any explanation.
Though this idiom is commonly used in many different places, there are some areas in which the phrase is unfamiliar. When a person from one of these regions hears these words, he might imagine the speaker is literally in hot water and become confused. Eventually, the speaker or another party will need to explain what the phrase means to help clear up his confusion.
For those who are unfamiliar with this idiom, considering some examples may help to understand how the phrase is typically used. One example could be a situation in which a person has broken the law and has to go into court to defend himself. When such a person says he is in hot water, what he really means is that he is in trouble with the law.
Another example could be a person who has forgotten to prepare some very important paperwork for his boss. If the office is closed and he has no way to fix the problem, he may realize that he is going to have to face his boss the next day and explain the situation to him. When this person says he is in hot water, he means he is expecting his boss to be unhappy with him when he hears the news. He may even mean that he fears he will lose his job.