How Wet Is Our Planet?
The answer may surprise you...
The Midwest was inundated by floodwater this spring. New Orleans was swamped by Hurricane Katrina. We hear constantly about the melting of polar ice caps and the rising of our oceans.
Sounds like we have plenty of water, right?
In a way, sure. The amount of water on Earth is relatively constant. It simply changes its physical state – cycling from a liquid to a gas inside a cloud or a solid in an iceberg. But a more meaningful way to look at water is to ask how much of it is available to humans and other terrestrial life. In other words, how much fresh water is on Earth?
Here’s an interesting and fun project that illustrates just how little water we have, and really stresses the critical importance of conserving what we have. It’s a project that’s borrowed from the educational curriculum Project WET and is geared for students in grades 4 through 6, but I’ve successfully led younger kids through the exercise and there’s a lot of value for adults, too.
Here’s what you need:
Time: 20 to 45 minutes
Materials: Six plastic jars or other containers, all about the same size (those institutional-sized pickle or mayonnaise jars work great) for each group of four to six students. You also need enough water to completely fill one of the containers. You’ll need masking tape, magic markers (Sharpies work great), an eyedropper and at least one plastic or Styrofoam cup for each set of jars. I also like to have a map of the world or a globe at the front of the room.
Procedure: You are going to have your own set of jars. Before students arrive, using the masking tape and markers, label each of your jars with these categories: Oceans, Groundwater, Lakes, Clouds, Ice, Rivers. Then turn the jars so that students can’t see the labels as they sit down.
Once students arrive, divide them into groups of four to six and hand out the jars, the tape and markers. One of the jars should be completely full of water.
Then tell the students that you’ll be testing their knowledge of the amount of water on the planet. Referring to the map or globe, ask them where one can find water on Earth. Use the analogy of an alien coming to earth. Where would they find water. Then lead the students toward the following categories:
– Oceans (surface water)
– Ice caps and glaciers (frozen or solid water)
– Groundwater (subsurface water)
– Lakes and ponds (surface water)
– Clouds (atmospheric or vaporous water)
– Rivers and streams (surface water)
The students will have plenty of other categories such as swamps, creeks, reservoirs, but try to steer their answers to the above categories. Then write their responses on a chalkboard. Then have each group label and mark each of their six jars with the categories.
Next, have all the students work as a group to arrange the jars on the table or desk from the source with the greatest amount of water to the source with the least amount of water. Make sure each group has consensus and that each member of the group helps the effort.
Make a simple chart on the chalkboard showing the six categories and ranking that each group gave them. Most groups will show the oceans as the most abundant source, but there will be little consistency after that.
The instructor (you!) will then arrange his or her jars in the following (correct) order: Oceans, Icecaps, Groundwater, Lakes, Clouds, Rivers.
It’s always fun to see how each group reacts to this order, and it’s fun to go around the room and have each group talk about their order.
Now is the toughest part of the project. Tell the students that they must determine how much of the earth’s water supply is in each of the categories. The full jar of water represents all of the earth’s water, and the job of the students is to divide the whole into each of the six categories. Pour water from the full contaainer or use the cup to divide it. This won’t take long but will be boisterous and a little messy. Remember, each member of the group has to agree on the apportionment.
When all groups have finished dividing their water, the instructor demonstrates the correct amount of water in each category:
– Oceans 97.3%
– Ice 2%
– Groundwater .6%
– Lakes .009%
– Clouds .001%
– Rivers .0001%
In order to build some suspense, and make this an interactive process, start with the oceans and have the groups hold up their jars representing oceans. Tell them that to start with, you’ll pour about half the water into the oceans, then fill the other jars in the proportions noted below, then pour the remaining water into the ocean jar. This technique helps build excitement into the activity instead of simply dumping 97 percent of the water immediately.
Have each group show its ice jar, then the instructor should fill his or her jar to the correct level. If you have about a gallon of water, this amounts to a little more than 2 tablespoons! Hold up this amount for the students to see, then have the students hold up their ice jars. Most will have greatly overfilled their jars.
Repeat this procedure for each of the remaining categories. Here are the amounts of water for each jar:
– Oceans 1 tablespoon
– Lakes 10 drops
– Clouds 2 drops
– Rivers .1 drops! (basically just a tiny droplet on the tip of your finger)
Then pour all the remaining water into the Oceans container.
Discussion: The key to this project is to illustrate the very small amount of
useable water on the planet. You can drive this point home by holding up each jar and asking about the water in it. Is this water fresh or salt? Is this water useable or unusable for humans?
You can discuss the physical states of water – for instance, icecaps are fresh water but unavailable for humans. Same with atmospheric water. Compare the amounts of water in each category. Discuss how much of the earth’s water is actually available to humans, and finally how much of this water is already polluted.
Oceans have abundant water, but it’s not readily useable to sustain humans. Groundwater is available only once it’s pumped to the surface. That leaves river and lake water that’s available to sustain most life on the planet. You can talk about impairments of this water – pollution from human waste, oil spills, etc. And then talk about water waste. How many students leave the faucet on while they brush their teeth? How many wash their cars every week? Have them talk about ways to conserve, clean and appreciate the little water we have.