All the water that exists on our planet has been almost endlessly cycled and recycled through its various forms throughout the history of the earth. Evaporating from water into the atmos-phere as gas, condensing and falling to the ground as rain, snow, or ice, and then sometimes forming the massive ice caps and glaciers found at the poles.
Approximately 71% of the earth’s surface is covered with water, lending the planet its nickname, the "blue planet”. Depending on environmental temperature, water changes between three states: solid (frozen), liquid, and gas. If all of the water on, in, and above the earth were drawn together into a sphere, it would encompass 332,500,000 cubic miles; of that, freshwater would be 2.5 million cubic miles, and freshwater on the surface a mere 22,000 cubic miles.
In liquid form
Liquid water has fixed volume, and must exist in between the temperatures at which water freezes and boils. This is—quite obviously—the form of water most useful to human beings for hydration.
96.5% of the liquid water on earth is found in its oceans; just 3% of the total water—in any form—on earth is freshwater. 30% of freshwater is stored underground, and just 1.2% of it is easily accessible on the surface, in lakes and rivers.
In solid form
Water as ice holds its shape and has a fixed volume. As water freezes (which occurs at 0 degrees celsius, or 32 degrees Fahrenheit), it expands; ice takes up more space than liquid water. It also floats on top of liquid water.
68.7% of the freshwater on the planet is ice, found in glaciers and in the icecaps at the north and south poles.
In gas form
When water is in an evaporated, gaseous form, it takes the shape and volume of the container that it is in. Water turns to gas at 100 degrees celsius (212 F).
3% of the water on earth is in vapor form, and found in the atmosphere.
Sources of National Ocean Service :
National Aeronautics and Space Administration : http://exploration.grc.nasa.gov/education/rocket/state.html