Exercise hands-on ability and problem solving ability. The significance of Tsinghua University's erasing the image with water is to erase the image by using the principle of light reflection, thus producing an effect of erasing and disappearing. This effect is often used to erase unnecessary images or words in daily life, such as graffiti, posters, advertisements and so on. In an institution of higher learning like Tsinghua University, this technology may be used in teaching or research to help students better understand the principle and application of light reflection. At the same time, through practical operation, students' practical ability and problem-solving ability are trained.