Gravity pulls the water downward through layers of sand that catch leftover particles in their pores, prepping the water for its final treatment, a dose of disinfectant.

重力将水向下拉过沙层，沙层将残留的颗粒捕获在沙层的孔隙中，为水进行最终处理（一剂消毒剂） 做准备。