It is a very old expression. Hot water was used five hundred years ago to mean being in trouble.

VOA: special.2009.05.10

He speaks in a language of math and it is very important for students to be able to have hot copies so that they can take notes on the paper rather than be working very hard to copy down the equations that he used in these lectures.

他以数学语言授课,所以发给学生教学材料,是非常重要的,这样就可在纸上做笔记,而不用拼命,抄下他在课上,用到的等式。

麻省理工公开课 - 媒体、教育、市场课程节选

that may seem hot here it's a little hard and the dialogue is very interesting in that point cuz the prince says: "I know you think you can love me."

也许有爱情的成分,这有点为难,那些对话也十分的有趣,王子说：,我想你认为你可以爱我“

麻省理工公开课 - 电影哲学课程节选

It is also important to wear a hat and sunscreen lotion to protect your skin from being burned by the very hot African sun.

VOA: special.2009.08.19