This activity can be used with any age level, from elementary level students to adult groups.

Educational Standards:
Earth and Space Science: Structure of Earth System

• Water, which covers the majority of the Earth's surface, circulates through the crust, oceans, and atmosphere in what is known as the "water cycle"
• Fresh water, limited in supply, is essential for some organisms and industrial processes. 4B/M8*

Classroom Activity

This activity is designed to introduce participants to the concept that although about 70% of Earth’s surface is covered by water, only a small fraction of that water is available to humans as an essential resource.

Engage:

Show participants a picture of the Earth taken from space to begin a discussion about water on Earth and how we have learned about water on Earth from satellites in space.

Show students the following image and use the following questions as discussion starters:

Earth's western hemisphere seen from space by the MODIS instrument on NASA's Terra satellite.

• What do you see in this image? (land, water, clouds)
• How was this image taken? (on a satellite from space)
• Do you think there is more land or water on Earth?
• Why?

Explore:

Direct the conversation toward the value of water to humans and other living organisms on Earth.

Questions to steer this discussion:

• What are some of the ways that you use water every day?
• Where does the water that you use come from?
• Is water a finite or infinite resource? How do you know?

Explain:

Share the following information with the participants. Have participants work in small groups to discuss the information, or lead the discussion to ensure they are reading the graphic information accurately. Begin by having them read the following information from NASA’s TRMM web site:

Water is essential to life, as it nourishes our cells and removes the waste they generate. Water determines whether plants produce food, or whether they wither from drought or rot from dampness. Water is essential to our homes and factories, to our production of food, fiber, and manufactured goods, and to just about everything else we produce and consume. Although water covers more than 70 percent of the Earth’s surface, only about 3 percent is fresh water—and about 69 percent of that is inaccessible because it is frozen in glaciers and icecaps.

Rainfall is one of the most important weather and climate variables that determine whether humankind survives, thrives, or perishes. Water is so ever-present on planet Earth that we often take it for granted. Too much water results in devastating floods, and the famine caused by too little water (drought) is responsible for more human deaths than all other natural disasters combined. Water comprises more than 75 percent of our bodies and as much as 95 percent of some of the foods we eat 1.

Next, share this graphic with the participants and have them discuss the information:

Some younger audiences will need help interpreting the graphic data. Be sure they understand that each image to the left represents only a small portion of the image before it. Take time to discuss some of the vocabulary.

Guiding questions could include:

• What does “saline” mean? How does salinity affect water for human usage?
• What is “groundwater”? How does water get into the ground?
• What is a “glacier”? Where do we find glaciers on Earth?
• What is “atmospheric water”?
• What do you think “biological water” might be?

Evaluate:

Ask the participants to think about their perception of Earth as the “Water Planet”, and then to think about how much of that water is actually accessible for us to use. Have them consider what the implications might be knowing that although Earth has a lot of water, only about 1% is available to humans as a freshwater resource.

Extend:

Have participants discover how much water is in an apple. They should peel the apple, and then weigh and record the weight. Now put it in a dry location, leave it for about two weeks, and then weigh it again. Have students determine the percentage of weight that has disappeared. Ask them to explain why the apple weighs less now.