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The Water Cycle
You’re thirsty! You run and get a cold glass of water to quench your thirst. Now, take a
good long look at the water. Can you guess how old it is?
The water in your glass may have fallen from the sky as rain just last
week, but the water itself has been around pretty much 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.
When kings and princesses, knights and squires took a drink from their
wells, your glass of water was part of those wells.
And you thought your teachers were OLD!
The earth has a limited amount of water. That water keeps going around and around and
around and around and (well, you get the idea) in what we call the "Water Cycle".
This cycle is made up of a few main parts:
 evaporation and transpiration
 condensation
 precipitation
 collection
Evaporation and Transpiration
Every hour of the day, the sun is shining on some part of the Earth. As it shines, it provides a
lot of light and heat. This heat warms up the water on the ground of the Earth, turning it from
liquid water to a gas or vapor. The vapor rises from the ground and rejoins the earth’s
atmosphere. So, evaporation occurs when the sun heats up water in rivers or lakes or oceans
and turns it into water vapor, which then goes into the air.
Evaporation takes place over every body of water, no matter what size. Water evaporates
from lakes, ponds, streams, oceans, and puddles. If you dry yourself in the sun after
swimming, the water from your skin is evaporating and rising into the sky. Imagine the water
from your own body becoming part of a cloud!
Do plants sweat?
Well, sort of.... people perspire (sweat) and plants transpire. Transpiration is
the process by which plants lose water out of their leaves. Transpiration gives
evaporation a bit of a hand in getting the water vapor back up into the air.
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Condensation
All over the world, water is heated until it becomes water vapor and rises into the sky. Along
with countless drops of water, our atmosphere is full of tiny particles. Some of these particles
come from pollution, and others are simply dust. The water vapor collects around these
particles and forms larger droplets. This process is called condensation, and it occurs when
water vapor in the air gets cold and changes back into liquid form. As more and more drops of
water condense around particles, a cloud begins to form.
You can see the same sort of thing at home... pour a glass of cold
water on a hot day and watch what happens. Water forms on the
outside of the glass. That water didn't somehow leak through the
glass! It actually came from the air. Water vapor in the warm air
turns back into liquid when it touches the cold glass.
Precipitation
Clouds cannot remain in the sky forever. As the size and number of water
drops grow, the cloud becomes too heavy and must shed some of its
weight. The water droplets begin to fall to the ground as rain. If the water
drops freeze before reaching the ground, we get snow, sleet, or hail.
Whether frozen like snow, or wet like rain, water falling from clouds to the
ground is called precipitation.
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, two things can happen to the groundwater:
 it will either soak into the earth by filtering through rock and
sand and become part of the “groundwater” that plants and
animals use to drink (this process is called percolation)
 or it may run over the soil and collect in the oceans, lakes, or
rivers (this process is called surface runoff).
Once it is back under the heat of the sun, the water will
evaporate. It begins its path to becoming a cloud once again!