31 States in the Gulf of Mexico Watershed
More than 70 percent of the Earth's surface is covered by water. But of all that water, about 97 percent is salty ocean water - - great for squids, but hard to process for use by landlubbers like us. Of the remaining three percent of Earth's water, more than two-thirds is frozen in glaciers and polar ice sheets. That leaves less than one percent of the water on Earth for our use - - and most of that water is groundwater, which is water stored underground in porous rock and loose sand and gravel. The activity that follows will give you an idea of how limited good, clean fresh water is - - and how much we rely on it.
(for students in Grades 4-8)
To demonstrate how limited freshwater is
5 one-gallon jugs; 2 glass jars; measuring cup
Fill five one-gallon jugs with water. Place them at the front of the room. Imagine that this water represents all the water on Earth. How much of the five gallons do you think represents fresh water (use a cup for a measure)? (Discuss the percentages of salt water and fresh water described above.)
Now pour 2 ½ cups from one of the gallon jugs into jar number one. This amount represents all the fresh water in the world. From this jar, measure 3/4 of a cup into jar number two. What's left in jar one represents all the fresh water that is inaccessible because it is frozen in polar ice caps. The 3/4 cup in jar number two represents all of the fresh water available to us for drinking and other uses. (Remind the class that much of even this little bit of water lies deep in the earth and is not easy for us to reach in economical ways.)
Where do you find fresh water? Does it look clean and drinkable?
(Extracted from the National Geographic Society Teacher's Handbook - Geography: Reflections on Water)