Water Resources  Elmhurst College
Ground Water  Chemistry Department
   Virtual ChemBook


Click for larger image 

World Water Resources / Supply

Introduction:

Water is a major and probably the most important chemical on earth. Water covers 71 % of the surface of the earth. Most living organisms contain 60-65 % water by weight.
 
Although water is readily available on earth, only a very tiny fraction is usable as fresh water. Of all of the water on earth, 97% is salt water in the oceans and seas. The remaining 3% is fresh water, most of this is inaccessible in ice caps, glaciers, or buried deeply below the surface. Only about 0.003 % is available for various uses as fresh water. Fortunately, this actually represents a generous supply of water which is continuously collected, purified, and distributed in the hydrologic cycle (see graphic in next panel).
 
The graphic above gives a comparison in relative numbers if all of the water in world is represented by 26 gallons. The usable fresh water amounts to only about 1/2 teaspoon.


Click for larger image 

Hydrologic Cycle:

The graphic on the left is a good study in the various phases of water as it exists and cycles in nature from the solid, liquid, and gas states.

Various physical process terms are also indicated which show the changes in the physical states of water.

Melt - solid to liquid state
Freeze - liquid to solid state

Evaporation - liquid to gas state
Condensation - gas to liquid state
Precipitation - a general weather term usually meaning water as rain.