Environmental Education in the Schools (Peace Corps, 1993)
 Activities, activities and more activities

### Our watery world

 OBJECTIVES: Diagram the water cycle. Explain why the supply of water on earth is finite. Describe the breakdown of fresh and salt water on earth. AGES: All SUBJECT: Science MATERIALS: Diagram of the water cycle, one clear gallon container and two small clear jars.

Photographs of Earth taken from the perspective of outer space reveal a watery world. This image coincides with a commonly held conception of water abundance. Ours is a water-rich planet. Problems we encounter with water shortages arise due to unequal distribution breakdown of fresh and salt water on earth, and unwise use of this life-sustaining resource. This investigation begins with a study of the water cycle. Students will see that the water we use on Earth today is the same water that filled the water jugs of the ancient Egyptians. Water moves in a closed system with no additional inputs from the atmosphere. We will never have more water on Earth than we have today

THE WATER CYCLE

Start this activity by discussing the cycling of water on earth. The immensity of the cycle is illustrated in the following figures. (Help your students visualize the size of a cubic mile before discussing these figures. For example, eight city blocks equal one mile. Students could try visualizing a cube eight city blocks in length, width, and height.)

* At any given moment, an average of 3,100 cubic miles of water droplets and water vapor is distributed throughout the atmosphere.

* Once every 12 days all of the moisture in the air falls as precipitation and is subsequently replaced.

* Ninety-five thousand cubic miles of water are evaporated into the atmosphere annually: 80,000 from oceans and 15,000 from land.

* This is balanced by 95,000 cubic miles of precipitation that fall back to the Earth.

After reviewing the diagram of the water cycle on page 216 and discussing these figures, ask your students to diagram the global water cycle using arrows and labels to explain how the cycle flows.

WHERE THE WATER IS

In the face of such water abundance, why are there water shortages? The breakdown of fresh and salt water on the planet is outlined on the top of the next page.

DISTRIBUTION OF EARTH'S WATER

 LOCATION PERCENTAGE Ocean 97.3 Fresh 2.7 Distribution of fresh water: ice caps and glaciers 77.2 ground water and soil moisture 22.4 Lakes and wetlands 0.35 atmosphere 0.04 stream channels 0.01

Source: Water Management for Arid Lands In Developing Countries, A. K Biswas et al, p. 10

The following demonstration could be used to help your students conceptualize the breakdown of fresh and salt water. Fill a large, clear container with 100 ounces or 12½ cups of water. This represents 100% of the Earth's water. Pour 3 ounces into a small, clear container to roughly the percentage of fresh water on the planet. From the three- ounce container, pour 2¼ ounces into a third container. This represents the amount of water in ice caps and glaciers. The water remaining in the second container represents the percentage of water available for our use. You might want to label the containers beforehand so students can refer to the labels as you demonstrate.

If you wish to use metric units in the demonstration, begin with three liters of water to represent the Earth's total water. Then pour 90 milliliters into a second container to represent the percentage of fresh water. From the 90 milliliters, pour off 67½ milliliters into a third container to represent the amount of water in ice caps and glaciers. The amount remaining in the second container represents the amount available to us for fresh water uses.