United States                          Office of Water                  EPA 810-F-98-001 !
               Environmental Protection                 4601                          June 1998

               AND CONDENSATION

               GRADE LEVEL: 4-7
               BACKGROUND: The following demonstration illustrates how the water cycle helps to purify water.
               The key terms are evaporation and condensation. Evaporation is defined as the process through which a
               liquid becomes a vapor. Condensation is the process through which a vapor becomes a liquid, and is the
               opposite of evaporation. In the case of water, the main mechanisms for evaporation and condensation are
               heating and cooling, respectively.
               MATERIALS NEEDED:
               4 cups of dirt or sand
               a dozen stones
               2 quarts of water
               a large glass bowl with tall sides (mixing bowl)
               a short glass
               clear plastic wrap
               a sunny day.
               PROCEDURE: Mix the dirt (or sand) and water in a large bowl. Stand a clean and empty short glass in
               the center of the bowl. Place the bowl outside in the sun. Cover the bowl with the plastic wrap and weigh
               down the edges with the remaining rocks. Place one rock on the plastic wrap directly over the cup. Allow
               the bowl to remain in the sun for several hours. Look in the cup (it should contain some relatively clean
               water free of mud). Look in the bowl (it should contain the dried dirt).
               FOLLOW-UP QUESTIONS:

               1. What are the two processes responsible for purifying the water? (Evaporation and Condensation)

               2. Where else do you see condensation? (Cold drink outside on a hot day)

               3. How does this process work on Earth?

               4. What is the plastic wrap? (Our atmosphere)

               5. What is the condensation? (Clouds and rain)

               6. What would happen if the plastic wrap was dirty? (Air pollution)

               VARIATIONS:  Add food coloring to water to demonstrate that this process does not remove all
               pollutants. This may be done simultaneously with the procedure above.
                                                           U.S. Environmental Protection Agency
                                                           Region 5, Library (PL-12J)