In vegetated areas, rainwater and runoff trickle through the soil, which cleanses the water of fecal bacteria and viruses, as well as many other pollutants.

• 在有植物生长的地方，雨水和迳流会慢慢流入土壤，于是水中的粪便细菌、病毒，以及许多其他污染物得以清除。