MORE INFORMATION- WATER

Distribution of the Earth’s Water

Figure 1: Distribution of Earth’s Water
(Source: Gleik, P. H., 1996: Water resources. In Encyclopedia of  Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823)
 
This graph shows where water is distributed on Earth.

  • The green column on the left shows that 97% of the water on earth is salt water located in oceans, seas, salt water lakes, bays and other salt water bodies, the other 3% is fresh water which we can live on.  
  • The brown column in the middle shows that 68.7% of fresh water  is in icecaps and glaciers (frozen water) which means it is not available for most animals and plants. Thus frozen water equals 1.74% of the total (fresh and salt) water on Earth. 30.1% of fresh water on earth can be found underground. This water is known as groundwater. Some groundwater is accessible for humans, plants and animals and some of it is not accessible for use. The last small amount that makes up the total freshwater on Earth is our surface waters (0.3%). Surface water is all the water we see on the Earth’s surface that is not salt such as lakes, rivers, creeks and wetlands.
  • The blue column on the right shows the final breakdown of the 0.3% Surface Water which is part of the 3% of Fresh Water on Earth. This means we are now looking at approximately 0.021% of the total   water (fresh and salt) on Earth. This is NOT a lot of  water. Of the tiny amount of water that makes up our freshwater (0.3%) 87% is in lakes, 11% in swamps and 2% in rivers. This is where we get most of the water that we use on a daily basis.


Table 1: Percentage Vs Volume Water Table
(Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823)

Water Source

Water Volume (in cubic kilometres)

% of Fresh Water

% of Total Water

No. of Olympic- Sized Swimming Pools (total water)

Oceans, Seas and Bays

1,338,000,000

--

96.5

5300 trillion

Ice caps, Glaciers & Permanent snow

24,064,000

68.7

1.74

9.6 trillion

Groundwater (total)

23,400,000

--

1.70

9.3 trillion

Groundwater (fresh)

10,530,000

30.1

0.76

4.2 trillion

Groundwater (salt)

12,870,000

--

0.94

5.1 trillion

Lakes (total)

176,400

--

0.013

70,000 million

Lakes (fresh)

91,000

0.26

0.007

36,000 million

Lakes (salt)

85,400

--

0.006

34,000 million

Atmosphere

12,900

0.04

0.001

5,100 million

Swamps

11,470

0.03

0.0008

4,500 million

Rivers

2,120

0.006

0.0002

840 million

The table above shows you where water is located on Earth with the approximate volume of water at each location (in kilometres cubed) and its percentage of the total fresh water and overall total of water on Earth.  The Olympic-sized swimming pool column is for your reference so you can visualise how much water that actually is.  The top of the table shows where the most water is located with the bottom showing where the least amount of water is located.

As you can see most of the water on Earth is located in oceans, seas and bays with rivers containing an extremely small amount of the total water on Earth.  Oceans, seas and bays alone contain the same amount of water as 5300 trillion Olympic-sized swimming pools.  This is enough water to cover just the area of the Central Coast, which has an area of 1772.9km2, to a depth of 755,000km which would stretch to the moon and back twice!!

It is important to note at this point that oceans, seas and bays are not fresh water bodies and icecaps and glaciers contain water that humans cannot get access to.  This means that according to this graph the best water supply on Earth comes from our groundwater resources with our lake systems the next best option.  Fresh groundwater sources worldwide contain approximately 10,530,000km3 of water or 4.2 trillion Olympic-sized swimming pools.  This amount of water would cover the Central Coast in a depth of 5939km of water.

The Great Artesian Basin which is the major groundwater source in Australia provides water to areas of Australia that do not have a reliable, or any, surface water source, covers approximately 22% of Australia, and contains approximately 64,900km3 of water.  This is the equivalent to approximately 26,000 million Olympic-sized swimming pools and would cover the Central Coast to a depth of 366km.

This information is valuable as it allows us to become aware of the fact that although our planet appears to have endless water resources and more water than we could want this is in fact not the case.  The water available to the ever increasing world population and the environment is located in very small sources which need to be preserved for future generations to not only enjoy but to survive.

This table is a guide only as the percentages are approximate as water is always in movement through water cycle and it is almost impossible to make exact calculations. 

     

Figure 2: How much of Earth’s water is usable by humans?
(Source: http://ga.water.usgs.gov/edu/earthwherewater.html)

The pie chart above shows a further representation of how water is distributed on Earth.  The mostly blue pie chart is all the water on Earth while the mostly maroon pie chart is the amount of water that is usable by humans.  When expanded out the mostly maroon chart shows the amount of the useable water is contained in groundwater, fresh water lakes and rivers.  In this pie chart we are looking at the same information that was presented in the green and blue columns of the previous bar graph.  The green column is the same as the blue section in the pie graph and the blue column is the same as the maroon section in the pie graph.  This pie chart shows you how we are going from the total amount of water on the Earth (salt and fresh) to the tiny amount of fresh water that is useable by humans.  This gives us a great picture of how even though there is a huge amount of water on Earth there is only a tiny slice that is available for human consumption.