What is runoff?

• A. Water absorbed by soil
• B. Water beneath the ground
• C. Rain and melting snow that becomes surface water
• D. Water used for irrigation

Answer: (C)

Runoff is the portion of precipitation that doesn’t soak into the ground. When rain or melting snow falls on land, some water infiltrates the soil to replenish groundwater and some is taken up by plants and returned to the air, but the remaining water moves over the surface of the land. This surface flow travels into streams, rivers, and lakes and is what we call runoff. It’s important to recognize that runoff can carry dirt, nutrients, pesticides, and other pollutants from the land into surface water, which is a key reason why watershed protection matters for drinking water quality. Runoff is different from water absorbed by soil (infiltration) and from groundwater (water beneath the ground), and it isn’t about water used for irrigation.