The answer is "drops of water turn into ice."
Explanation: There is a piece of ice underneath when water drips from the faucet, which means that after the water drips down, it turns into ice. The corresponding idiom is "dropping water turns into ice".
Drip of water turns into ice. It is an idiom that describes that when the weather is very cold, water will turn into ice when it drops.
Extended content:
Drips of water turn into ice
[Source] Song Dynasty Qian Yi's "New Book of the South": "It is cold in the winter, and drops of water turn into ice."
< p>[Usage] This expression can be used when the weather is very cold.[Example] There is a difficult part. When the weather turns to ice, you have to wash your dirty clothes in the water hole. You also hate the dirty clothes and curse them.
★Ming Dynasty Feng Menglong's "Yu Shi Ming Yan" Volume 27
Reference: Baidu Encyclopedia Drops of water turn into ice