EARTH’S FRESHWATER RESOURCES: Snow as a water source

Overview

Students observe various forms of water (clouds, Greenland ice sheet, oceans) in a photo of the Earth from space and watch a teacher-led demonstration illustrating the distribution of Earth’s water resources, emphasizing the very small amount of Earth’s water that is fresh water and available to humans and ecosystems. 

This activity is an abbreviated version of several related lessons from the National Oceanic and Atmospheric Administration (NOAA) addressing water resources, water use, and water conservation.

Background/reference

Freshwater Availability lesson plan. No date. Precipitation Education, Global Precipitation Measurement Mission, NASA. https://gpm.nasa.gov/education/lesson-plans/freshwater-availability-classroom-activity  

Earth’s Water lesson plan. No date. Precipitation Education, Global Precipitation Measurement Mission, NASA. https://gpm.nasa.gov/education/lesson-plans/earths-water 
Where Is Earth’s Water? 2021. USGS Water Science School, U.S. Geological Survey. https://water.usgs.gov/edu/gallery/watercyclekids/earth-water-distribution.html

Materials

Included in kits unless otherwise noted

● NASA photo of Earth from space, laminated

● measuring cups (1 x 2 cup measure, 1 x ½ cup measure)

● ice cube trays (2) – packaged with ice and water activity materials

● optional: simple water cycle diagram poster

● 5 gallon bucket full of water.

● Optional: School can provide a globe.

Procedures 

1. Engage/activate prior knowledge

Ask students to think about the lesson topic by posing questions such as “What are some of the ways that you use water everyday?” and “Where does the water that you use come from?” (from NASA Freshwater Availability classroom activity)

2. Observing water on planet Earth

Display Earth “blue marble” photo. (Photo source: NASA Freshwater Availability classroom activity)

Ask students to make observations and share what they notice with the group (when called upon, in an orderly fashion!). Draw their focus to WATER in the image. What are the blue areas? (Oceans, which are made up of water.) 

One of Earth’s nicknames is the “Blue Planet.” Why do you think this is? What makes it the blue planet? (About 70% of Earth’s surface is covered by water, which appears blue.)

But not all water appears blue in this photo. What are the white swirled areas? (Clouds, which contain water droplets or ice particles.) What about the solid white area in the upper right portion of the photo (Snow on the Greenland ice sheet – water in its solid forms.)

Water is one thing that makes the Earth so special among all of the planets. All living things need water to survive. As far as scientists know, water is not present on most planets.

3. Introduction to freshwater as a limited resource

Referring to the photo, ask if we would want to drink the water in the oceans? Why or why not? (No. It is salt water, and it does not help our bodies the way that fresh water does. Most living things can’t use salt water for survival. Similarly, farmers can’t use salt water to water crops.)

Introduce the idea that even though there is a lot of water on Earth, most of that is salt water that is in the oceans. 

It turns out that even though there is a lot of water on Earth, it’s mostly (97%) salt water. The amount of fresh water is only a small portion of the total water on Earth (3%), and that is the only water that people and land-based ecosystems can use.

4. Visually represent the distribution of Earth’s water resources

The following demonstration is adapted slightly from the NASA Global Precipitation Measurement Mission lesson plan, “Earth’s Water.”

The demonstration starts with a 5-gallon bucket filled with water. Tell the students that this represents all of the water (100%) on Earth.

We just learned that most of the water on Earth is salt water; the rest is called freshwater. We are going to focus on freshwater. Remove two cups of water from the bucket (in e.g. a liquid measure). These two cups represent all of the freshwater on Earth, which makes up 3% of Earth’s total water supply. Move the bucket representing the oceans out of the way, since we are only considering freshwater from now on. 

Ask students to share ideas about where/in what forms freshwater can be found on Earth. Suggestions might include lakes, rivers, glaciers, snow fields/ice, permafrost, aquifers/underground, as water vapor in the atmosphere/in clouds. Guide them toward identifying polar ice caps/glaciers as containing water in its frozen form. 

Remove ½ cup of water from the 2 cups of water representing all freshwater. Pour the remaining 1 ½ cups of water into an ice cube tray. The 1 ½ cups of water in the ice cube tray represent the amount of freshwater that is stored as ice in glaciers and polar ice caps (and therefore not available for use by humans). 

Focus on the remaining ½ cup of water. This represents the liquid freshwater that is in the ground, surface waters (rivers & lakes), and water vapor in the atmosphere. So if the 5 gallon bucket represents all of the water on Earth, this half cup shows how much of that total (1%) is freshwater that is available to use.

Optional: Explain that not all of the ½ cup of water is clean and usable by humans (for consumption). Use an eye dropper to remove one drop of water from the ½ cup. This drop represents the amount of freshwater that is clean and available for humans to use.

5. The sources of freshwater

We have learned that living things need freshwater to survive, and that besides the freshwater that we need to drink, cook, and wash, humans use freshwater for growing the food that we eat, generating electricity (hydroelectric power), making just about anything that we buy and use from paper to clothing to cars (Isaiah, 2014).

We have also learned that only a small amount of Earth’s total water can be used by humans for these things.

So where does the water that we use come from? (Lakes, streams, groundwater) And where does that water come from? (Rain, snow)

Header image: Courtesy NOAA