Groundwater is used for drinking water by more than 50 percent of the people in the United States. If groundwater becomes polluted, it will no longer be safe to drink.

When it rains or large amounts of snow and ice melt, the liquid water flows into the watershed. This movement of water is known as runoff. Along the way, the flowing water picks up loose liquids and other materials, such as lawn chemicals, cleaning products, and gasoline.