Large temperature difference between indoor and outdoor: The temperature difference between indoor and outdoor often leads to the temperature difference between the ground and the air, especially in the extreme temperature of winter or summer, which will make water vapor condense on the ground and form water droplets.

High humidity: indoor humidity is high, for example, in rainy season or excessively humid environment, condensed water droplets are easy to form on the ground.

Ground material: Some special ground materials, such as casserole, can absorb heat and store heat energy. When cold air meets a hot casserole, it will condense into steam and then form water droplets.