Equipment required: One or more buckets of water (or access to a garden hose connected to a water supply). Pour one or two buckets of water (or run water from a garden hose) on bare ground (grass or soil is OK). Observe how the water moves. Some of the water may soak into the ground and some may flow over it. Pour a few more buckets (or run more water from the garden hose) over the same area and observe any differences in the behavior of the water. Does it still soak into the ground? Discuss how the moisture conditions in the soil will affect how much water gets absorbed. Would water be more likely to run off after the ground has been saturated by a heavy rainstorm? Discuss what happens to the water that gets absorbed into the ground.

Repeat the demonstration on a paved surface such as a driveway or sidewalk and document the differences. With no soil to absorb this water, what would happen in a heavy rainstorm? How would an engineer in charge of a city’s flood control system prepare for the runoff generated on paved parking lots and roads in a heavy rainstorm?