To avoid pollution of rivers and lakes, Beijing in the Yuan dynasty (1206-1368) had sewers two storeys tall, and even in the Qin dynasty (221-206BC) cities had clay sewage pipes.
為避免河流、湖泊水源被汙染，元朝北京就有了兩層樓高的汙水下水道；甚至秦朝城市就有了陶土製的下水道。