Even though the earth contains an abundance of water, only a small percentage is fresh water. An even smaller amount of this freshwater is accessible to the people and animals that need it. As the human population grows, the amount of freshwater available per person shrinks. The relatively small amount of available freshwater demonstrates how critical it is for everyone to help maintain clean, healthy lakes and streams.
Grade Level: 4-8 grades
- 5-ESS2-2 Earth’s Systems. Describe and graph the amounts and percentages of water and fresh water in various reservoirs to provide evidence about the distribution of water on Earth.
- MS-ESS3-4 Earth and Human Activity. Construct an argument supported by evidence for how increases in human population and per-capita consumption of natural resources impact Earth’s systems.
For alignment, see: Water Quantity NGSS Summary
- Experience the relative scarcity of freshwater on the planet.
- Explain why some of the earth’s water is not easily accessible.
- Compare and contrast surface water systems and groundwater in regard to their relative sizes as Earth’s freshwater reservoirs.
- Manipulate simple tools that aid observation and data collection, make accurate measurements with appropriate units.
- Use tools and equipment appropriate to scientific investigations.
- Conduct scientific investigations using appropriate tools and techniques.
How much water is available?
- Oceans and seas contain more than 97% of the water on the planet. Because it is salt water, it is not healthy for humans and animals to drink.
- The remaining 2.5% of water on Earth is fresh water.
- Of that, the amount of freshwater available for use by living beings is very small. For instance, about 70 percent of Earth’s freshwater is “locked” in ice caps and glaciers.
- Most of the remainder of freshwater on earth — about 30% — is present as soil moisture, or lies in deep underground aquifers as groundwater and is not accessible.
- That leaves less than 1% of the world’s water accessible for use. This is water found in lakes, rivers and underground sources that are shallow enough to tap into at an affordable cost.
- Of that, the Great Lakes contain 20 percent of the world’s surface freshwater.
Because the water system is a “closed” system, the Earth’s supply of water remains the same. The planet has as much water as it will ever have. Yet world population continues to grow. The relatively small amount of available freshwater supports more than 7 billion people. As this number increases, the amount of fresh water available per person decreases. Thus maintaining the quality of the Earth’s available fresh water is vitally important.
Amount of water in each major reservoir on earth:
- Saltwater in oceans: 97.2%
- Ice caps and glaciers: 2.14%
- Groundwater: 0.61%
- Surface water: 0.009%
- Soil moisture: 0.005%
- Total: 100%
- Can You Spare a Drop? Measuring Freshwater
Summary: Students remove measured amounts of water from a five-gallon bucket, simulating the amount of fresh water available on earth.
Time: One 50-minute class period