THE WATER CYCLE

Water continues to move around the atmosphere in a never-ending cycle.  This means that water on the earth today was here when the dinosaurs and pre-historic man were alive! Just think: a caveman may have drunk the same water you are drinking right now.

Water is constantly being recycled and re-used.  It is taken up into the atmosphere by a process called EVAPORATION.  Molecules of water break free and are taken up into the air from the lakes, dams, rivers and streams,  Evaporation takes place at all temperatures.  The water molecules continue to travel upwards, gathering to form clouds.

PRECIPITATION occurs when the water condenses and forms droplets (rain) or frozen particles (snow) and falls to earth once more.  When the rain or snow reaches the earth, it runs off to form surface water, such as lakes, and helps to fill our rivers and dams.  Rain water or melted snow may also be absorbed into the soil through a process called PERCOLATION as it moves downwards through openings in the soil to replenish AQUIFERS under the ground.

Some areas receive more precipitation than others.  Those areas are usually close to oceans or large bodies of water that allow more water evaporate and form clouds.  Other areas receive less.  Often these areas are far from water or near mountains.  As clouds move up and over mountains, the water vapour condenses to from precipitation and freezes.  Snow then falls on mountain peaks.  This usually only happens in winter.

Plants also give off water into the ATMOSPHERE through the process of TRANSPIRATION.  Because of this water cycle, water is always present in the air around us and is called RELATIVE HUMIDITY.