Introduction: Earth as seen from space is clearly a water planet. About 71% of the surface of the planet is covered by water. Water is found in the oceans, rivers, ponds, lakes, groundwater, ice caps, glaciers, and in the atmosphere as water vapor and clouds. Water changes state and moves from place to place through the water cycle of evaporation, condensation, and precipitation. Although earth’s water supplies seem almost limitless when viewed from an ocean beach, water forms only a thin film on the surface of the planet. The average depth of the oceans is about 3.5 – 4.0 km, while the average radius of earth is 6371 km.
What to Expect: Some of these volumes are so small the class will need to gather around the display to see the water being added. The clear bottles with blue colored water in them clearly labeled, make a dramatic display for the school or community.
Materials:
– Seven two-liter bottles
– Food coloring
– Water
– Labels for bottles
– Graduated cylinders
– Calibrated droppers for 1 ml.
Procedure:
1. Color about 2 liters of water blue with food coloring.
2. For younger students: have students measure out the volumes, add each amount to a separate bottle. (For older students: have students use these figures to calculate volumes. Students can fill the bottles and set up a display for the school in a prominent place.)
| Type of Water | Percentage of Earth’s Water Supply | Volume of Water to Use in Bottle |
| All of the earth’s water: | 100 % | 2000 ml |
| All earth’s salt water (oceans) | 97.2 % | 1944 ml |
| All earth’s fresh water: | 2.8 % | 56 ml |
| Fresh water locked up as ice | 2.3 % | 46 ml |
| Underground fresh water | 0.4 % | 8 ml |
| Surface fresh water | ~ 0.05 % | 1 ml |
| Water in soil and air | ~ 0.01% | 0.2 ml |
Evaluation:
- Students can make a bar graph showing the percentages of water in different forms.
- Students can calculate volumes for each percentage, answering the question, “If ocean water volume is about 1,360,000 km3, what is the volume of water in each of the other categories?”
Extensions: Have students calculate the average volume of water used per person per day in your community. How much water is used by the community annually?
Copyright 1998-2008 by Sea Education Association, all rights reserved. Compiled and edited by Pat Harcourt & Bill Meyer.
This project was supported, in part, by the National Science Foundation (Proposals # TEI-8652383, TPE-8955214, and ESI-925324), the Henry L. and Grace Doherty Foundation, the Donner Foundation and the Pew Charitable Trusts. Opinions, findings, conclusions or recommendations expressed are those of the authors and not necessarily of the Foundations.
