Water Cycle
​The central theme of hydrology is how the water circulates. This is called the water cycle. The water cycle is also known as the “hydrologic cycle“.

​Pour yourself a glass of water and take a sip. Did you know that the water you’ve just swallowed is the same water that wooly mammoths, King Tutankhamun and the first humans drank? That’s because Earth has been recycling water for over 4 billion years!

The world’s water moves between lakes, rivers, oceans, the atmosphere and the land in an ongoing cycle called – you guessed it! – the water cycle. As it goes through this continuous system, it can be a liquid (water), a gas (vapour) or a solid (ice).

Lets take a  look at the different stages of the wonderful water cycle…
Evaporation
​Energy from the sun heats up the surface of the Earth, causing the temperature of the water in our rivers, lakes and oceans to rise. When this happens, some of the water “evaporates” into the air, turning into a gas called “vapour“. Plants and trees also lose water to the atmosphere through their leaves. This process is known as “transpiration“.
Condensation
​As water vapour rises up high into the sky, it cools and turns back into a liquid, forming clouds. This process is called “condensation“. Currents high up in the air move these clouds around the globe.
How does Water Move?
  1. ​Water in the oceans, rivers and lakes evaporate to become water vapor (gas).
  2.  When the water vapor reaches a point in the sky where it is cold enough, it forms condensation/water droplets. These water droplets join together to form clouds.
  3.  As more water droplets join the cloud, the cloud becomes heavy. When the cloud is heavy enough, the water droplets will precipitate back to earth as rain or snow.
  4.  After a rainstorm, the water is collected in collection areas like streams, rivers, and under ground in aquifers.
  5.  This water cycle repeats itself over and over again.
Precipitation
​When too much water has condensed, the water droplets in the clouds become too big and heavy for the air to hold them. And so they fall back down to Earth as rain, snow, hail or sleet, a process known as “precipitation“.
   Fun Fact: Water can change from a solid to a gas, without becoming a liquid first. Through this process of “sublimation” our planet's ice can evaporate directly into the air without melting!
Collection
The fallen precipitation is then “collected” in bodies of water – such as rivers, lakes and oceans – from where it will eventually evaporate back into the air, beginning the cycle all over again. How it is collected, depends on where it lands…Some will fall directly into lakes, rivers or the sea, from where it will evaporate and begin the cycle all over again. If the water falls on vegetation, it may evaporate from leaves back into the air, or trickle down to the ground. Some of this water may then be taken up by the plant roots in the earth. In cold climates, the precipitation may build up on land as snow, ice or glaciers. If temperatures rise, the ice will melt to liquid water and then soak into the ground, or flow into rivers or the ocean. Water that reaches land directly may flow across the ground and collect in the oceans, rivers or lakes. This water is called “surface run-off“. Some of the precipitation will instead soak (or “infiltrate”) into the soil, from where it will slowly move through the ground until eventually reaching a river or the ocean.
Try This!
Questions/Discussion
  • What do you observe?
  • If you only watered the soil in our terrariums once; how did the water get on the lid? Take your lid off the terrarium and feel the soil. Why is the soil still wet? Do you think that any water has evaporated from the soil? Why? If water evaporated, where did the evaporated water go? Did it ever rain in your terrarium? How do you know? Where did the rain come from? Is there anything in your terrarium that reminds you of a cloud or cloud drops?
  •  Why is this happening? When the sun hits the window, it heats up the water in the bag. That water turns into a gas through the process called evaporation.
  • In nature, evaporated water vapor goes into the atmosphere, but in our bag, it has nowhere to go, so it ends up sticking to the sides of the bag, turning back into a liquid as condensation. That condensed water then slides back into the pool of ​water below as “rain”. This is known as the water cycle.
  •  Keep checking back on your experiment a few times a day, or anytime it’s sunny ​to see the water cycle progress.​
Family Connection
  • Send the water cycle bags home with the children with a note explaining the water cycle.​
  • Have families make a terrariums together. A terrarium is usually a sealable glass container containing soil and plants and can be opened for maintenance to access the plants inside. The family will be able to observe the water cycle happen in the terrarium as the water continuously recycles itself just like on Earth. 
  • Make it a Science Experience: Make three identical terrariums. You have to use the same kind of container, the same amount of soil & the same plants. Make your variable (the thing you are going to test) the amount of water you put into the terrariums. Measure a different amount of water into each terrarium. Close the lids and watch the terrariums over several days to see which amount of water made the best environment for your plants. A terrarium with too little water will have dry plants. A terrarium with too much water will have plants with yellow leaves and maybe even mold growing on the soil!
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