Water Resources of the United States

PROCEDURE

1. Fill one 1,000-mL graduated cylinder with colored water to the 1,000 mL line. Tell the students that this represents the Earth's entire supply of water. Pour 28 mL of the total water into a second 1,000-mL graduated cylinder. The 28 mL of water represents the Earth's total freshwater supply. The remaining 972 mL of water is saltwater that occurs primarily in oceans.

   972 mL EARTH'S SALTWATER

   28 mL EARTH'S FRESHWATER

2. Divide the 28 mL of freshwater by pouring into smaller containers; 23 mL for icecaps and glaciers, 4 mL for ground water, 2 drops for surface water, and 1 drop for the water in the atmosphere and soil.

   ICECAPS, GLACIERS 23 mL

   GROUND WATER 4 mL

   SURFACE 2 DROPS WATER

   ATMOSPHERE AND SOIL 1 DROP WATER

3. List the percentages of Earth's water on the chalkboard or overhead projector. Refer to these numbers as you continue.

Interpretative Questions

As the students examine and compare the different volumes of water in the graduated cylinders, ask the following questions:

1. Which of the four freshwater graduated cylinders represents the most freshwater on Earth?
   ANSWER: 23mL, representing icecaps and glaciers.

2. Is this the source of freshwater commonly used bt humans for drinking, watering the lawn, cleaning, etc.? Explain.
   ANSWER: No, icecaps and glaciers are usually too far away from population centers.

3. Approximately what percentage of the Earth's freshwater is ground water?
   ANSWER: 4 mL/28 mL x 100 = 14% ground water.

4. Where is most of Earth's water found?
   ANSWER: Oceans.

5. Can cities such as San Francisco, Miami, and New York City, which are near oceans, use the water from the oceans for households and industry? Explain.
   ANSWER: No, the ocean water contains salts that are harmful to humans, kill plants, and corrode metals.

6. Can the salts be removed from water? Why isn't this commonly done?
   ANSWER:Yes, but the desalinization process is very expensive.

7. Why is the little bit of water in the atmosphere important to plants, animals, and humans?
   ANSWER: Water in the atmosphere is carried inland in the forms of rain, snow, sleet, and hail which supply freshwater sources such as lakes, streams, and ground water.