define runoff water
RECOMMENDED LESSONS: Runoff. Runoff is precipitation that did not get (infiltrated) absorbed into the soil, or did not evaporate, and therefore, made its way from the ground surface into places that water collect. Runoff causes erosion, and also carry chemicals and substances on the ground surface along to the rivers where the water ends up. It can cause water pollution too. Only about 35% of precipitation ends up in the sea or ocean. The other 65% is absorbed into the soil. Some of it too will evaporate.