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 resource—without 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?
     Show me the answer
     Hide
     China, India, and the United States
   • How is this map different than a "normal" display of geographic data?
     Show me a description
     Hide
     The area of each territory in this cartogram shows the proportion of worldwide water used by that territory.
   • Why would it be important to compare this visualization to a similar one that shows population?
     Show me an explanation
     Hide
     Comparing the water use cartogram to a population cartogram helps users compare if a territory uses a lot of water because it has a lot of people, or if it has fewer people who all use a lot of water.
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.
   
   
   

   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.
   • USGS Where is Earth's Water?
   • Circle of Blue's All the Water in the World
   • UNEP Vital Water Graphics - A World of Salt

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.