8.4: Water Issues

The Water Cycle

All of the water on Earth has always been here and therefore, is the same water that was used by our ancestors and even by the dinosaurs.  This is because water continually changes form as part of the water cycle (also known as the hydrological cycle).  There is no beginning or end to this cycle but water within it does transform into different states (solid, liquid and gas) as it moves between the stages as ice, snow, rain, mist and vapour.  Water is the ONLY substance on Earth to naturally exist in all three states (solid, liquid and gas).  Amazingly, the same water that was once flowing down a river, could now be stored in a glacier, a kangaroo or inside a piece of fruit! The water in a tomato today may once have been drunk by a Tyrannosaurus Rex or been bathed in by the ancient Romans!  In short all the water on Earth has been and will be recycled again and again until the Earth is no more.

Water has the chemical formula H2O.  This means there are two hydrogen (H) atoms for every one oxygen (O) atom.  It is colourless, tasteless, odourless and is a liquid at room temperature (this is 25⁰C) and pressure (this is 1 atmosphere).  Water boils at 100⁰C and freezes at 0⁰C.  Frozen water is 9% lighter than liquid water which is why it floats.

Water helps to keep the Earth's climate steady as the oceans are able to store a vast amount of heat energy and ice at the poles and other regions reflects solar radiation.

For more information on the water cycle, check out  WI-How the water cycle works

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Outcomes
8.4.3: Students learn to describe the water cycle in terms of the physical processes involved.