In agricultural societies, things which are filtered out with water are all organic matter that can be broken down and returned to the natural cycle. Thus, in several places in north Taiwan which are relatively short of water, the agricultural irrigation system and the town or village drainage system were linked together, so that water could be circulated and reused, thus saving water resources.
「水由天上來」，農業社會中，經水淘洗過的萬物都是可以消化、回歸自然的有機物，因此在北部幾個水資源缺乏的地方，農業灌溉系統與鄉鎮的排水系統合一，如此還可循環再利用，節省水資源。