Water is a crucial ingredient for life on Earth: It nourishes people, plants, and animals and plays a major role in the planet's weather and climate. The water cycle is Earth's natural mechanism for transporting, cleansing, and recycling water between the surface and the atmosphere. In this lesson, students recognize the different forms that water takes and learn about where it exists in the environment. Through class discussion and experiments, students model the water cycle and explore how it can be used to create fresh water.
- Understand that water exists in the environment in different forms
- Identify the ways that water moves through the environment
- Recognize that most of Earth's surface is covered by water but that only a small amount is fresh water
- Produce fresh water from salty water by distilling it
Grade Level: 3-5
Two to three class periods
- Water Phases Flash Image
- Global Water Distribution Flash Interactive
- Observe Precipitation QuickTime Video
- Water Cycle Animation QuickTime Video
- The Hydrologic Cycle Flash Interactive
- Biome in a Baggie QuickTime Video
- Solar Still Part I: Salt Water QuickTime Video
- 1 bowl of water
- 1 bowl of ice
- Per pair of students for biome activity:
- Bottom half of a 2-liter plastic bottle
- 1 cup of pebbles
- 2 cups of potting soil
- 1 gallon-size re-sealable plastic bag
- Pinch of seeds (grass, beans, etc.)
- 1 cup of water
- Per team of students for solar still activity:
- 1 large mixing bowl
- 1 coffee mug
- 1 small rock (or other small weighted object)
- 1/4 cup of salt
- 1 pitcher of water
- 1 large spoon (or other stirring utensil)
- Plastic wrap
- Drinking cups
Before the Lesson
Familiarize yourself with the videos so that you will know when to pause them. Organize the materials into kits for each pair/team. Prepare a small dish of salt solution a few days in advance so that it has time to evaporate and leave behind salt crystals.
Part I: Water Basics
1. Begin by asking the class, "What is water?" Record their responses on the board. Then ask:
- Can water come in different forms?
- What are some examples of each form?
2. Show the Water Phases Flash Image. Discuss the three phases of water. Allow students to handle some liquid water and ice. Explain that water vapor is invisible but present in the air. Then ask:
- Did we see all the different phases in the slideshow?
- Can you think of any more examples to add to our list?
3. Discuss where each form of water is found on Earth. Ask:
- Where do you find solid water on Earth?
- Liquid water?
- Water vapor?
4. Show the Global Water Distribution Flash Interactive. Discuss the main difference between water in lakes and rivers (fresh water) and water in the ocean (salt water).
Part II: The Water Cycle
5. Discuss what precipitation is and the different kinds of precipitation. Show the Observe Precipitation QuickTime Video. Ask:
- Where does precipitation come from?
- Why do you think there are different forms of precipitation?
- What happens to rain/hail/snow when it reaches Earth's surface?
6. Discuss how water is continuously cycled between Earth's surface and the atmosphere. Show the Water Cycle Animation QuickTime Video once in its entirety. Play the animation again, pausing at each transition to have students explain what is happening to the water in each stage.
(Optional) For older students, discuss the steps of the water cycle in more detail by going through The Hydrologic Cycle Flash Interactive together.
7. Show the first segment of the Biome in a Baggie QuickTime Video. (Stop before the host starts assembling the biome.) Ask students what they think she is making. After the class has discussed the project, continue to play the video to show the assembly instructions. Stop before the explanation about how the biome works.
8. Have students work in pairs to create their own biome in a baggie. Distribute the supplies and lead the class through the steps. After the biomes are assembled, discuss how the water will move and if this is similar to the way water behaves on Earth. Ask:
- How will the water move from the soil to the plant?
- How will the water get into the air?
- How will the water move from the air back to the soil?
- How does the biome in a baggie represent Earth?
9. Show the rest of the Biome in a Baggie QuickTime Video and compare your class discussion with the explanation given.
10. Optional) Have students make observations of their biomes over the next few days. Ask:
- What has happened to the seeds?
- Why don't you need to water the plants?
Part III: Making Fresh Water from Salt Water
11. Review the major steps in the water cycle: evaporation, condensation, and precipitation. Have students discuss the importance of the water cycle in maintaining fresh water on Earth. Ask:
- How does the water cycle affect your everyday life?
- Does water ever disappear and leave Earth and its atmosphere?
12. Explain that the class is going to conduct a second experiment related to the water cycle. Remind students that water exists on Earth in both salt and fresh water forms, but that the fresh water supply is very limited. The task here is to find a way to make salt water into drinkable fresh water. Break the class into teams to brainstorm solutions. Show, but do not distribute, the supplies that are available to them.
13. Discuss the ideas that the groups come up with. Show the first two minutes of the [Solar Still Part I: Salt Water video], stopping before the explanation of how the still works. Distribute the supplies and have the teams assemble their own solar stills. Note: Remind students to keep the cups clean to avoid contaminating the experiment.
14. Discuss how the solar stills will purify the salty water. Students should recognize that when water evaporates from a solution, the solute stays behind. As an example, show them your prepared dish of salt crystals left behind after a salt solution has had time to evaporate. Show the end of the Solar Still Part I: Salt Water QuickTime Video, and compare your class discussion with the explanation given.
15. Place the stills in a sunny location and check on them in a few hours. If you are comfortable with it, allow students to taste their distilled water. Discuss how the distillation process of the solar stills is related to the water cycle. Note: There probably won't be much water distilled in just a few hours -- let the stills work for a few days to produce more fresh water.
Check for Understanding
Have students discuss the following:
- What role does water play in your life?
- In what forms is water found on Earth and in the atmosphere?
- What is a cycle? What is the water cycle? Can you give two or three examples of other types of cycles?
- Do you think the term cycle is a good description of how water behaves on Earth?
- Do you think a solar still could make fresh water from orange juice? What about from other liquids?
The Digital Library for Earth System Education (www.dlese.org) offers access to additional resources on this topic.