Where's the Water?

Part A: Worldwide Water Distribution

True-color mosaic of Earth as viewed by NASA's Terra satellite. NASA Photo.

The World Water Council, gives this description of the importance of water for life:
"Water is life. All living organisms are predominantly made of water: human beings about 60%, fish about 80%, plants between 80% and 90%. Water is necessary for all chemical reactions that occur in living cells(it) is essential for food production and all living ecosystems."

It's clear that water is a critical resourcewithout it, life cannot survive. Explore the following graphics and tables to develop a sense of where Earth's water is and which parts of it are available for supporting life.

  1. Take a look at a visualization of estimated annual water consumption for territories around the world. (Linked page will open in a new window)
    • Examine the cartogram and read the caption. Open the Population Map for comparison with the Water Use map.
    • Which countries are the largest consumers of water?
    • How is this map different than a "normal" display of geographic data?
    • Why would it be important to compare this visualization to a similar one that shows population?
  2. Three-quarters of Earth is covered with water, but most of it is not available for human use. In general, salty water and frozen water (ice) aren't useable unless large amounts of energy are used to transform them into fresh, liquid water.

    The table below shows estimates of where Earth's water is. Do the math with a calculator, or download this spreadsheet file (Excel 2007 (.xlsx) 11kB Aug6 18) and use it to answer the following questions.
    Table of World Water Distribution

    Stop and Calculate

    1. What percentage of the world's water is fresh?
    2. Of Earth's total volume of fresh water, what percentage is frozen?
    3. How much of the world's fresh water is in liquid form on its surface?
    4. Which of the five water sources in the chart is readily available for human use?
  3. Compare your answers from above to the following graphics prepared by various organizations to show Earth's water.

Optional Hands-on Activity

Use the numbers you calculated or the ones from one of the graphics you viewed to set up a physical demonstration of where Earth's water is. Start with a fairly large volume of water (10 liters or more) to represent all of Earth's water. Calculate the volumes that would represent fresh water, frozen water, groundwater, and surface water. Use smaller containers to demonstrate the distribution.