THE WATER CYCLE

We are surrounded by water - in the sea, in rivers and lakes, underground, in living things and in the air. This water is constantly moving from one *water source to another. As it moves, it may change from liquid water into a solid (ice or snow) or a vapour, or back again. But the total amount of water on the Earth stays the same. How it moves and changes is called the water cycle.

Get a glass of water and put it on the table next to you.  Take a good  look at the water.  Now -- can you guess how old it is?  The water in your glass may have fallen from the sky as rain  last week, but the water itself has been around  as long as the earth has!  
When the first fish crawled out of the ocean onto the land, your glass of water was part of that ocean.  When the Brontosaurus walked through lakes feeding on  plants, your glass of water was part of those lakes.  

                                                                                                                                                                                           

The earth has a limited *amount of water.  That water keeps going around and around and around and around. That's the reason why we call it "Water Cycle".



The cycle consists of  different parts. Let's see them:

But, before learning about each stage, see this power point presentation. Click here.
Have you got a clear idea of the water cycle? Now, we are going to explain it step by step.
The water cycle has no beginning and no ending, but we are going to start with "Evaporation"

EVAPORATION

Evaporation is when the sun heats up water in rivers or lakes or the ocean and turns it into vapor or steam. The water vapor or steam leaves the river, lake or ocean and goes into the air. Look at the photo.

Does water evaporate only from rivers, lakes and oceans? No, people sweat (perspire and plants transpire, that is, plants lose water out of their leaves). This process is called transpiration. The combination of *evaporation and *transpiration is called evapotranspiration. Look at the photo.

CONDENSATION

The process in which water vapour changes into a water droplet or ice crystal is called *condensation. This happens because water vapor in the air gets cold and changes back into liquid, forming clouds. See the photo.





PRECIPITATION

Precipitation occurs when so much water has condensed that the air cannot hold it anymore.  The clouds get heavy and water falls back to the earth in the form of rain, hail, sleet or snow
Different types of *precipitation:


rain
 
snow
 
hail

sleet



COLLECTION

When water falls back to earth as precipitation, it may fall back in the oceans, lakes or rivers or it may end up on land.  When it ends up on land, it will either soak into the earth and become part of the “ground water” that plants and animals use to drink or it may run over the soil and collect in the oceans, lakes or rivers where the cycle starts all over again.

Different types of *collection:

- *Surface run-off the excess of rain flows over the land

- *Infiltration/Percolation (groundwater flow or groundwater recharge): process where water moves downward from surface water to groundwater.

*GLOSSARY

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PRACTICE

1. Let's see if you have understood the water cycle. Click here
2. Complete the chart

The Word Starts With this Letter Hint Answer
W A substance that is very important to us. We need it to live, and it covers over two thirds of the surface of the Earth. _____________________________
O A large body of water on the surface of the earth. _____________________________
E A process in which liquid water turns into water vapor (a gas). _____________________________
P In transpiration, water from these objects evaporates into the atmosphere. _____________________________
C A fluffy-looking object in the sky that contains tiny water droplets or ice particles. It is formed when water vapor condenses. _____________________________
R This type of precipitation is water that falls from clouds in a liquid state. _____________________________
S This type of precipitation is water that falls from clouds in a fluffy, frozen state. _____________________________
R A large, flowing body of water that usually empties into a sea or ocean. _____________________________
W The process in which water circulates from the oceans to the clouds to the land to the rivers, and then accumulates back into the oceans. _____________________________

Check

3. Complete the blanks in the paragraph below (the first letters are already filled in)
    The water cycle describes what happens to water on the planet. Over the sea, water e..................... (1) into the air as w............(2) v................(3), which then r...................... (4) and c......................... (5), causing c..................... (6) and the formation of .......................... (7). Eventually, precipitation (for example r................... (8), s....................... (9) or h....................) falls.
Check

4. Watch this video that summarizes the water cycle very well. Use your earphones. Enjoy it!

5. Now, an interactive game to summarize what you have learnt