Rainwater running off roofs, lawns, streets, and parking lots can wash a variety of water pollutants into lakes and streams.

These pollutants include nutrients from garden fertilizers; bacteria from pet wastes and rotting litter; sediment from erosion; toxic chemicals from pesticides, gasoline, and trace metals from emissions and grinding car parts (lead, mercury, and cadmium); zinc from roofs and gutters; and road salt or sand.

Objectives
  • Define the term runoff.
  • Define the terms point and nonpoint source pollution.
  • Classify pollution sources as either point or nonpoint source.
Materials
  • Piece of brick, concrete, or asphalt
  • Piece of sod
  • Measuring cup
  • Tap water
  • 3 shallow baking pans
  • Trash bags
  • Poster board
  • Glue
Instructions
  1. Place a piece of brick, concrete, or asphalt and pieces of sod into separate shallow pans and set the pans on a table for the students to observe.
  2. Have students guess what will happen when water is poured on each surface.
  3. Pour one cup of water on the hard surface and have students describe what is happened, then repeat the procedure on the piece of sod.
  4. Explain that the excess water that does not soak is called “runoff”.
  5. Have students relate this experiment to what happens to runoff in a city. Runoff occurs more often in areas where there is concrete, paved roads, or other hard surfaces, and much less in areas covered with vegetation.
  6. Pet waste is often carried in the runoff, as well as litter, oil, chemicals, and pesticides.
Topics for Discussion

Discuss how litter contributes to urban water pollution by having the students describe what kinds of litter they frequently see in their community and what happens to it after a heavy rain. Then have students create a plan for their community to reduce the amount of litter in their area.