Activity: Can You Spare a Drop? Measuring Fresh Water
Summary: Students remove measured amounts of water from a five-gallon bucket, simulating the amount of fresh water available on earth.
- 50 minutes
- 5-gallon bucket
- 2-cup transparent measuring cup
- 1-cup transparent measuring cup
- 1 eyedropper
Before class starts, fill the 5-gallon bucket with water. Have the other materials nearby in a place where the whole class can observe.
Note: Be sure to wipe water off the floor if spills occur during this activity.
- Explain to students that the water in the 5-gallon bucket represents all the water on Earth. Ask them to name the kinds of water that exist in, on or around Earth. They should be able to name rivers, lakes, oceans, clouds or water vapor, ice caps, groundwater, water held in soil, and water held in plants and animals. Provide hints so that all types of water are mentioned.
- Ask two students to come up and help with the demonstration. Ask one of them to remove two cups of water from the bucket, using a measuring cup. Have the student hold that amount so everyone in the class can see it.
- What does the water in the cup represent?
- What does the water in the bucket represent?
- Saltwater. Explain that the saltwater is not usable by humans because drinking it would make us very sick.
- Move the bucket aside. Ask the first student to pour 1/2 cup of water into the one-cup measurer held by the other student.
- What does the 1-1/2 cups still left in the two-cup measurer represent?
- Polar ice caps. Explain that this water is unavailable for our use because it is frozen.
- Set this cup aside. The first student can return to his or her seat.
- Ask the class what the 1/2 cup of water represents.
- Groundwater, surface water (e.g. lakes, rivers, wetlands), and water vapor in the atmosphere.
- Have the class guess how much water should be removed from the cup to represent only the surface water on Earth. After a few guesses, pull out the eyedropper from your pocket and draw some water into it. Place one drop of water into the hand of a few students. Explain that one drop of water out of a whole 5-gallon bucket represents the water that is available to us and other animals for drinking.
- Allow the class to think about this for a minute.
- Then explain to them that the total amount of water on the planet is not going to change. Even though water moves around on the planet and changes from one kind to another, we will never have any more than we have right now.
Part 2 – Discuss the Results
Spend some time discussing the activity with the class. The following questions are a good place to start:
- Were you surprised at how little water is available for human use?
- Would you call water a scarce or abundant resource? Why?
- What do we need/use water for?
- Why can’t we drink saltwater?
- The number of people who need to use Earth’s freshwater keeps increasing. If the amount of freshwater cannot change, but there are more people who need it, what does that mean? What might happen?
- Can people and animals live without clean freshwater?
- What is the main cause of the increased demand for freshwater?
- Ask students to think about the term water quality. Find out from them what they think it means. If they get stuck, have them think about it in terms of low water quality or high water quality: would they want to drink, wash, swim or cook with low quality water or high quality water? Have them come up with as many descriptions as they can for what might be low quality and high quality water.
North Carolina Museum of Natural Sciences – Adapted with permission from the Girls in Science Program. Original source content: Hands On Save Our Streams – The Save Our Streams Teacher’s Manual, Chapter One, Watersheds, Water Water Everywhere and Not A Drop to Spare, Water Supply Activity, The Izaak Walton League of America.