The water cycle is continuous and has four stages: evaporation, condensation, precipitation and collection. While the idea of a cycle that is never-ending may seem complex for preschoolers to understand, breaking the discussion into individual parts will give them a better opportunity to learn how the earth reuses this natural resource and build a basis for further scientific discovery in later grades.
Evaporation is the process in which water changes to vapor. Help your class make a connection to this by explaining it is the same thing that happens when someone uses the shower at home. Heat causes steam to form and fill the room. In the water cycle, the sun helps the water evaporate. Take the class outside on a sunny day and put a drop of water on the blacktop. Wait for it to disappear and talk about how it evaporated into the air. Later, place two wet cloths on the windowsill, leaving one on a plate and putting the other in a sealed plastic baggie. Check them the next day, and point out that the bagged cloth is still wet because the baggie prevented the water from evaporating into the air, while the other cloth is now dry.
Condensation is the process in which water vapor in the air is changed back into liquid. Remind students of the steam from the shower. When the steam reaches the mirror, it fogs up and when the bathroom cools off, that fog turns into drops of water. Pass out small mirrors. Ask the preschoolers to breathe on the mirrors, explaining that their hot breath contains water vapor. Watch as the glass gets foggy. Then sit the mirrors on the table and watch as the fog turns into small drops of water.
Precipitation is water released from clouds in the form of rain, sleet, snow or hail. After water evaporates into the air, it condenses in the sky and forms clouds. Later, some of these drops of water fall to earth as precipitation. To demonstrate this, gather the preschoolers around you and place a clear glass jar where everyone can see it. Fill the jar with two inches of very hot water and cover the top with a plate. After a few minutes, place several ice cubes on top of the plate. The cold plate causes the warm air in the jar to form droplets, creating precipitation -- rain in a jar.
When water falls back to the earth, it can land in oceans, lakes or rivers and this is known as collection. Water that falls on land is also collected by soaking into the earth, becoming ground water for plants. On a rainy day, place a bucket or tub outside on the playground. When the rain stops, bring the bucket inside so children can see how much water was collected. This is what happens when precipitation falls into lakes and streams, continuing the water cycle. Challenge students to identify ways living things use water and use finger paints to create a class mural about the water cycle.
- Comstock/Stockbyte/Getty Images