Make a Water Cycle Model

Background Information for Teachers

Earth is a planet full of water. About 70% of the Earth's surface is covered by water, but water is not distributed equally on Earth. 97% of the water is found in the world's oceans; the remaining water is found in glaciers and ice, rivers, lakes, underground, or in the atmosphere. The U.S. Geological Survey (USGS) estimates that Earth's total water supply is about 326 million cubic miles (about 1,359 million cubic km) of water! Most of this water is liquid, but on Earth water can also exist as a solid in the form of ice or snow, and as a gas in the form of water vapor.

The water on Earth is in constant movement. This movement is not limited to Earth's surface, but also includes the atmosphere and the subsurface. The water cycle, also called the hydrologic cycle, describes how water moves within and on Earth and atmosphere and its transition from one state to another. The water cycle is dynamic and involves many different processes that contribute to water being moved from one place to another. Some of these processes are evaporation, condensation, precipitation, transpiration, and infiltration (Figure 1).

Image Credit: Wikimedia Commons, Alexchris / Science Buddies

A cross-section of a landscape including an ocean, green land, and snowy mountains. The sun is shown above the ocean. Clouds are shown above the land and the ocean. Blue areas depict rivers and lakes on the green land. Grey arrows show the movement of water from the ocean into the atmosphere, back onto the land and within the subsurface. Blue arrows visualize processes such as evaporation, transpiration, surface runoff, or infiltration. Blue dashed lines from the clouds to the ground visualize precipitation.

Figure 1. Schematic diagram of the water cycle. (Image credit: Water_Cycle_-_blank.svg: *Wasserkreislauf.png: de:Benutzer:Joooo derivative work: moyogo (talk) derivative work: Alexchris, CC BY-SA 3.0 , via Wikimedia Commons, image was edited to include transpiration and arrows for infiltration and surface runoff.)

The Sun is the major driver of the water cycle. Surface waters such as the ocean, lakes, and rivers are heated up by solar energy and thus, some of the liquid water evaporates and becomes water vapor. As warm air rises, that moist air rises to higher altitudes. In the process, it cools down and eventually condenses into water droplets. This process is called condensation. We see these tiny water droplets as clouds in the sky. The tiny water droplets within a cloud merge and become bigger and heavier until they get too heavy and fall down to the ground due to gravity. This process is called precipitation. If temperatures are too cold to keep the water droplets in a liquid state, they crystalize and form snow or ice crystals and fall to the ground as snow or hail. Snow that is deposited on mountains or glaciers can be stored as solid water for thousands of years until it gets warm enough for it to melt again. Ice and snow can also directly transform into water vapor in a process called sublimation. Gravity also causes liquid water to fall on land, and thus get absorbed into the soil through infiltration where it can be stored as groundwater or taken up by plants. Plants release some of the water back into the atmosphere through their leaves in a process called transpiration. Water that does not soak into the ground flows over the land as surface runoff until it enters a river, lake, or the ocean. Again, gravity is the driving force. These water bodies function as storage reservoirs for liquid water. It is from there that the water cycle starts again when the Sun's energy turns the water into water vapor.

The horizontal movement of water in the water cycle happens both in the atmosphere through clouds being moved around the globe by air currents, and through water flow on land as surface runoff or as waterflow in rivers or underground. Although water in the water cycle is constantly moving and continuously transforming from one state to another, no water ever disappears! The water that exists on our planet today is the same water that existed on our planet a thousand or a million years ago! The natural cycling of water is one of the most important processes on Earth, as it provides all living organisms with a continuous supply of fresh water. The water cycle also plays a significant role in the weather patterns on our planet, as it contributes to weather events such as precipitation or cloud formation. Without the water naturally recycling itself, life on Earth would not be possible!

In this lesson, students will explore some of the processes that are part of the water cycle in more detail. They will build a miniature landscape, including a water body inside a closed plastic box, and then use a heat lamp to mimic the Sun. In their model, students will be able to observe evaporation, condensation, precipitation, infiltration, and surface runoff in real-time. Based on their observations, students will be able to conclude that the water cycle is propelled by the Sun and gravity.

Additional Background Links

• Water Facts - Worldwide Water Supply, Bureau of Reclamation
• The Water Cycle for Adults and Advanced Students, U.S. Geological Survey (USGS)
• A Multi-Phased Journey, NASA Earth Observatory

Prep Work (15 minutes)

1. Prepare all the materials for each student group. You can gather each group's materials in their plastic box.
2. Print out the labeled Water Cycle Diagram, so you can show it to your students during the lesson.
3. Print out both Water Cycle Processes sheets for each student group and cut them apart along the lines to separate the process name, its definition, and the picture. Store all the cut-out pieces for each group in a re-sealable plastic bag.
4. Optional: If you have time, set up and run the experiment yourself before class to make sure the lamps you use generate enough heat and to gauge how long it takes for condensation and precipitation to take place in your model. You might also want to use your model to demonstrate how students should build theirs. Figure 2 shows an example of how you can set up the water cycle model. Notice how the lamp is directly over a body of water and the ice cubes are placed away from the lamp.

Image Credit: Svenja Lohner, Science Buddies / Science Buddies
Figure 2. Schematic drawing of a possible water cycle model setup.

Engage (15 minutes)

1. Start the lesson by encouraging the students to wonder about where the water that falls from the sky in the form of rain, snow, or hail comes from.

   Have you ever been caught in a rainstorm or surprised by heavy rain while you were outside?

   Most likely, all students can relate to a time when they were caught in the rain or a rainstorm. Have them share what it was like, where this happened, or how the rain felt, etc.

   How would you describe rain to somebody who has never experienced rain before?

   Elicit responses that define rain as water or water droplets that fall from the sky.

   Where do you think the water comes from that falls from the sky when it rains?

   Have students speculate. They might say that the rain falls from the clouds in the sky. In that case you might follow up with questions about clouds, what they are made of, where the water in the clouds comes from, etc. If they state clouds are water vapor, you can ask where this water vapor comes from. Encourage students to wonder how the water gets into the sky and why it falls back to the ground as rain.

2. Tell students that in this lesson, they will learn more about water, where we can find it, and how it moves around between land, the ocean, and the air or atmosphere. In the following, they will do an experiment in small groups in order to find out what processes contribute to water moving from one place to another.

Explore (60 minutes)

1. Divide your class into groups of 3–5 students. Provide each group with the materials they need to make their water cycle model. If you have built your own model, show it to your students as an example. Otherwise, explain what students should build. Within their model they should have:
   • A water body (ocean) with a large surface area (at least half of the box)
   • A rock, or mountain made from clay (mountain height at least half of the box height)
   • A patch of soil or sand. Some of the sand or soil will get wet from the water, but part of the sand surface should be dry.
   Students can choose how they arrange their landscape within the box. Depending on their configuration, they might be able observe different water cycle processes. Note: If you provide students with warm or room-temperature water, it will evaporate faster than cold water. Also, a water body with a large surface area and small water volume (shallow water) is favorable over a small water body with a large water volume, as shallow waters heat up much more quickly and thus, evaporate faster.
2. Let each group prepare their landscape within the box. Then tell them to close the lid and place the heat lamp about 30 cm above the box where the water is and turn it on. Tell students that the location of the lamp is not flexible, and must be above the water body. Make sure to mention to students that they should not be touching the lamp during the experiment, as it will get very hot over time! Have them fill the re-sealable bag with ice cubes and place the ice cube bag on top of the lid. They can place the ice cubes wherever they want on the lid, with the exception of placing the ice cubes directly underneath the heat lamp, otherwise they will melt too quickly. The placement of the ice cubes will determine where the condensation and precipitation in the water cycle model happens. Depending on where students decide to place them, they will be able to observe surface runoff (if the ice cube bag is placed on top of the mountain and water drops onto the mountain), infiltration (if the ice cube bag is placed on top of the sand or soil and water drips onto the sand or soil, or water runs from the mountain down to the sand), or neither of those (if the ice cube bag is placed on top of the water body and the water drips into the water body). If all the ice cubes within the bag melt in the first 15 minutes, they need to be replaced with fresh ones. An example water cycle setup is shown in Figure 2.
3. Once everything is set up, tell students to start their timer or watch the clock and monitor what happens in their water cycle model over time. Give students at least 30 minutes to observe their water cycle model. Ask them to record their observations on their Student Worksheet in 10-minute intervals. Tell them that they can move the bag with the ice cubes to check what is happening underneath and also touch the box from all sides with their hands to feel if anything changes, but students should not open the box during the experiment. Keep students engaged during their observation time.
   1. During the first 10-minute interval, ask each student group to form and write down a hypothesis of what will happen to the water inside their model and what they might observe. They should also reflect on how the model they created represents the real world by discussing the following questions.

      How does your model landscape reflect the real world?

      In your water cycle model, what does the lamp represent?

      In your water cycle model, what do the ice cubes represent?

   2. In the second 10-minute interval, give students the opportunity to look at other groups' setups, which might be different from their own, and encourage them to exchange thoughts, as well as their observations. Have students record on their worksheet how other water cycle models differ from theirs.
   3. In the third 10-minute interval, ask students to use the Figure on their worksheet to label what happens with the water in their model based on their observations so far. They should then think about how and where water appeared, how it moved, and indicate these observations with arrows in their diagram. Ask students to draw, using one color, what they can observe, and to use another color to draw the things they think are happening, or can see the results of but cannot observe directly (evaporation). Students should also discuss the following questions.

   What changes do you see occurring within your model?

   Do you see water appear or disappear within your model? If so, where?

   Can you name or describe some of the processes you are observing?

   Are there processes you think are happening but cannot observe directly?

   Why do you think these processes are happening?

   While students are working, walk around and check in with them. Listen to their discussions and provide support where needed. Engage students by asking them about their thoughts and observations.
4. Within the first 30 minutes, students should be able to observe the condensation of water underneath the ice cubes on the lid, as well as precipitation of water from the lid onto the mountain (making surface runoff visible), onto the sand (making infiltration visible), or onto the water body. Based on these observations, they should be able to conclude that water must have gotten into the air due to evaporation from the water body. They should have noticed that the area under the heat lamp got warmer or hot over time. Depending on what heat lamp you chose, it might take more or less time for all these processes to occur. If no water droplets drip from the lid as precipitation yet after 30 minutes, keep the experiment going while starting the Reflect section and encourage students to check back in with their experiment in between sections.

Reflect (45 minutes)

1. After students have finished and recorded their observations for the 30-minute mark, gather the class and have students share their observations. Specifically focus on observations that help explain how water moves among the water body, the land, and the atmosphere.

   What did you notice happening in your water cycle model?

   Let students describe what they observed. They should have been able to see individual water droplets forming underneath the bag of ice cubes (condensation), which then merged to become bigger droplets that eventually fell to the ground (precipitation). Ask students if any group saw water droplets form at other places in their box.

   Where do you think the water droplets came from that accumulated on the lid of the box?

   Listen to students' replies. Use their responses to point out that the water droplets must have come from the air. Tell students that in the air, water exists in the form of water vapor. Sometimes we are able to see this water vapor, like steam rising above a pot of boiling water or as mist, fog, or clouds in the air. Challenge them to think about where the water vapor inside their model came from. Then guide them to conclude that the energy of the heat lamp turned some of the water inside their model into water vapor. Students should have noticed that the part of the plastic box under the heat lamp where the water is became significantly warmer over time, and students can be reminded that very warm water produces visible water vapor. Less warm water still produces water vapor, just not so much that it is visible.

   Why do you think the water droplets only accumulated underneath the bag of ice cubes?

   Let students speculate why this is the case. They should state that the ice cubes significantly cool down the lid underneath. Any water vapor that comes in contact with the cool lid will transform from its gaseous state to its liquid sate. It might help to provide another example of condensation to which students can relate. Ask them if they have ever seen water vapor accumulating on a cold window to the point where it became misty, or a mirror in the bathroom steam up during a hot shower. These are examples for the same process that they have observed inside their box. Here, the result is an accumulation of water droplets on the cool lid surface.

   What happened to the water droplets over time?

   Students should have noticed that more and more water droplets accumulated over time. The water droplets started to merge and become bigger. Once they got too big and heavy, they fell to the ground.

   Does anybody know the names of the processes that you just described (the water droplets forming on the cold lid, the water body heating up and allowing water vapor to move into the air, and the droplets falling from the lid)?

   Students might already know the terms condensation, evaporation, and precipitation. Explain to them that all the processes they have just described and observed within their model are part of the water cycle, which describes how water moves within and on Earth and the atmosphere, including its transition from one state to another. Together with your students, define evaporation, condensation, and precipitation and have them point out and record on their worksheet where and why each of these processes happened within their water cycle model.

2. Help students make the connection between their model and the real-world water cycle.

   How do you think your water cycle model represents the water cycle that happens on Earth (on a much bigger scale)?

   What does the heat lamp represent?

   What do the ice cubes represent?

   Listen to students' responses as they compare their water cycle model to what happens on Earth. Use their replies to point out that the heat lamp represents the Sun, which heats up Earth and the water on Earth, and that the ice cubes represent cooler air layers higher up in the atmosphere. Have students describe how the processes they observed in their model happen on Earth.

3. Continue the discussion beyond what students observed in their experiment. Tell students that besides evaporation, condensation, and precipitation, there are many more processes involved in the water cycle. Ask students what other processes they know.

   What other ways that water moves around on Earth or changes states do you know?

   Can you think of other ways water can fall from the sky?

   What happens to rainwater that falls onto the ground?

   Collect students' answers. Have them describe each process that they mention.

4. Tell students that in the following activity, they will learn more about these additional water cycle processes. Provide each student group with a bag that contains the cut Water Cycle Processes Sheets. Explain to students that in the bag they will find the names, descriptions, and pictures of many of the processes that are happening in the water cycle. Their task is to match the name, description, and picture. They will also find an image that represents the natural water cycle on their Student Worksheet. Their goal is to find and label as many of the processes as possible within the water cycle image.
5. Give students 10 minutes to finish their task. Then review and label the water cycle diagram together. Have students share how they labeled their diagram and what processes they have identified. Give students the opportunity to describe the different processes in their own words. As a reference, you can show students the labeled water cycle diagram. This allows students to correct their diagram and ensures that each student has a correctly labeled water cycle diagram on their worksheet at the end of the class.
6. Based on their completed water cycle diagram, discuss the following questions.

   What are other processes besides evaporation, condensation, and precipitation that some of you observed in your water cycle model?

   What are processes in the water cycle that none of you observed in your model? What could we do to add them to the model?

   Have students consult their water cycle diagram while answering this question. Answers might vary depending on how they set up their water cycle model. Students who placed their ice cube bag above the mountain should have been able to observe surface runoff, students who placed their ice cube bag above the soil should have been able to observe infiltration and maybe percolation within the soil or sand. Ask students to add these processes to the table in their worksheet if they have observed them in their model. Examples of processes they could not be observed are transpiration or sublimation. One way to add transpiration to the model would be adding live plants to the box. Sublimation is hard to include in their model.

7. In the next step, question students about what would happen to the water cycle in their model if they modified their model.

   Now that you know more about all the different processes within the water cycle, can you tell me what would happen with the water cycle in our model... ... if we were to remove the heat lamp? ... if we were to remove the ice cubes? ... if we were to remove the water body (ocean)?

   Listen to students' speculations. Encourage them to think about what drives or fuels the water cycle. Use students' replies to emphasize that the water cycle—as well as the changes of water from solid, liquid, and gas—are propelled by sunlight. The energy that comes from the Sun is what causes the water to change its state from solid to liquid, or liquid to gas, and thus drives the water to cycle through the atmosphere, into and out of the oceans or over the land. Other processes, such as precipitation or surface runoff, are driven by gravity. On their worksheet, have students write down which water cycle process is driven by which force (sunlight or gravity). Note: The driving force of condensation would also be the sunlight, but in an indirect way, as the temperature difference causes the water to condensate.

8. Finally, discuss the cyclical aspect of the water cycle and its role in the world.

   Based on your observations, can you explain why the water cycle is called the water "cycle"?

   Guide students to conclude that the water cycle is dynamic. Water continually cycles among land, ocean, and atmosphere via evaporation, condensation, transpiration, and crystallization, and precipitation as well as downhill flows (runoff) on land. Have students provide specific examples. For example, water moves through the atmosphere by clouds that are moved by air currents (wind) and gets deposited back on land or the ocean through precipitation. Water on land moves downhill because of gravity and gets lifted up into the atmosphere via evaporation, etc.

   Why is the water cycle an extremely important process for our planet?

   Help students realize that the water cycle provides a continuous supply of water for all living organisms everywhere in the world. In the water cycle no water disappears; the amount of water always stays the same. This also means that the water that we have on Earth now is exactly the same water that has been there from the beginning (and that the dinosaurs already drank!). If water did not naturally recycle itself, we would run out of clean water, which is essential to life.

Assess

You can use this quiz to assess student learning after the activity:

• Online quiz, assignable in any LMS
• Quiz (pdf) and answer key (pdf)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Hydrologist

Add Favorite Remove Favorite More Menu

• Read More

Career Profile

Hydrologists examine the physical characteristics, distribution of, and circulation of water above and below Earth's surface. They study rainfall and other precipitation, how water moves through rocks and soil and its return to the oceans and air. A hydrologist might use remote-sensing technologies and models to monitor changes in regional or global water cycles, or they might study movement patterns of water to predict flooding events or droughts. Read more

Environmental Scientist

Add Favorite Remove Favorite More Menu

• Read More

Career Profile

Environmental scientists use their knowledge of the natural sciences to protect the environment, which includes Earth's water resources. They could, for example, plan and execute field programs to analyze the quality of surface water and groundwater or they could draft proposals about how to effectively manage water supplies to conserve water in a community. Read more

Lesson Plan Variations

• Together with your students, identify local geographic features, such as water bodies, mountains, or forests, and discuss how they relate to the water cycle.
• Make a connection between the water cycle and weather patterns. How does the cycling of water in and out of the atmosphere contribute to weather patterns on Earth?
• Make a connection between the water cycle and the global problem of freshwater depletion. If all this water is being recycled, why is there a shortage of potable water?
• Allow students to modify their water cycle models to include more water cycle processes or find out what happens if they change the setup, such as removing the ice cubes, the mountain, or the heat lamp.
• Explore the water purification aspects of the water cycle. Evaporation and condensation help purify water, as during evaporation contaminants and salts that are present in the water are left behind. Try out the Solar-Powered Water Desalination activity with your students to demonstrate how water gets purified via evaporation and condensation.
• Investigate individual water cycle processes in more detail, such as studying precipitation by making a rain gauge, having students make their own cloud, or letting students model and compare different water bodies.