mops the floor, and comes back to the machine, wash the cloth by itself, then the dirty water get injected into the other bottle. It keeps doing that until it runs out of clean water or until the cleaning duty is completed. At the end, you just pour away the dirty water. If you have dry food that left on a floor on a long time, it will not remove it. But if you have dust, the machine is doing fine to first 扫地 then 拖地. You do need to change the head between 扫地 and 拖地。It does a pretty good job overall.