Besides the standard function of water transport, the underground system of sewers and pipelines diverts rain waters and handles sanitation of water, transporting it to treatment plants.
除了輸入能量的管道外，地底下還有兩大排水系統：雨水下水道與衛生下水道。雨水下水道即一般所稱的排水管，接受地面水溝的汙水，注入河川。