Activity Overview: The water cycle is a global, natural example of the energy-water nexus, the integral relationship between the two resources. But you don’t need the whole world to see an example of this continually moving cycle. Putting the water cycle in a sealed plastic bottle is a tiny but illustrative example of many of the phases and also demonstrates how the Sun keeps the cycle going.
Pour a small amount of water (about ¼ c) into a clear plastic bottle and add a drop of food coloring if desired. Seal the bottle and place it on the window sill in the sun. Observe how the sides and top of the bottle begin to form a layer of water droplets. When the droplets are heavy enough, they drip down the sides and join the pool of liquid water at the bottom of the bottle.
Ask students to compare what they observed in the plastic bottle to the phases of the water cycle, and transformations of water that you have discussed in class. Which water movement is most similar to rain? What part of the bottle model represents the oceans and lakes?
What is the source of energy for the transformations happening inside this bottle?
The mini water cycle inside the sealed water bottle is a good model for the water cycle on Earth. With the cap screwed on, no water goes in and no water comes out. Make the connection for the students that just like the water in the bottle, Earth’s water is limited. Discuss what happens if the water in the bottle is dirty? What does this mean for pollution in Earth’s water?