Hydrosphere

The Water Cycle

The water on Earth is the same water that has always been on earth.  It is the same water that was used by our parents, grandparents, great grandparents.

 

Figure 1: The Natural Water Cycle
(Source: Auckland Council)

 

Are we using water that the dinosaurs used?

Yes we are drinking the same water that dinosaurs swam in!

This is because of the water cycle (also known as the hydrological cycle).  Like a circle the water cycle has no beginning or end.  Water within the natural water cycle will continue to circulate around and around.

 

Words to remember!

Evaporation: Change from a liquid to a gas

Precipitation: The general term for rainfall, snowfall and other forms of frozen or liquid water falling from clouds.

Condensation: Change from a gas to a liquid

 

How does the water cycle work?

The most important factor in the water cycle is actually the sun!  The sun heats the ocean (just a little bit) and then starts the continuous water cycle

  1. Some of the water (a liquid) on the surface of the oceans evaporates.  The evaporated water is now a gas and is called water vapour.

  2. Wind and air currents help the vapour to rise into the atmosphere.  The temperature is cooler high in the atmosphere so the water vapour condenses and forms clouds.

  3. When the weight of the condensed water in the clouds is too heavy the water falls to Earth as rain, snow, sleet or hail.  This is called precipitation.

  4. The precipitation that falls onto land either soaks into the ground (called groundwater) or it flows downhill into stormwater or surface run off.

 

The surface runoff flows into streams and rivers and then into lakes, dams or  the ocean.  Groundwater also flows in a downhill direction and some of it also ends up in water bodies such as rivers, dams and lakes because it soaks through the banks.  All of this water will always continue to move and eventually be returned to the ocean where the cycle starts again.

To learn more about the natural water cycle and the urban water cycle click here.

Why is the water cycle important?

One of the are many reasons why the water cycle is important is that it makes sure we always have a fresh water source available.

Did you know that…?

The water cycle will continue, although the amounts of water being transported may change over time, until the Earth stops spinning on its axis.  The amount of water being transported in the cycle is greatly affected by greenhouse emissions, population size and location, pollution and other man-made factors.

Water facts

  • Approximately 96.5% of all of the water on Earth is found in the oceans.

  • Each day the sun evaporates a trillion tons of water

  • Less than 1% of the water supply on earth can be used as drinking water


Australian Curriculum links

Year 7

Science Understanding  - Earth and space sciences

(ACSSU116)  Some of Earth’s resources are renewable, but others are non-renewable

(ACSSU222)  Water is an important resource that cycles through the environment