Precipitation, evaporation, and transpiration are
all terms that sound familiar, yet may not mean much to you. They are all part of the water cycle,
a complex process that not only gives us water to drink, fish to eat, but also weather patterns that help grow our crops.
Water is an integral part of life on this planet. It is an odorless, tasteless, substance that covers more
than three-fourths of the Earth's surface. Most of the water on Earth, 97% to be exact, is salt water found in the oceans.
We can not drink salt water or use it for crops because of the salt content. We can remove salt from ocean water, but the
process is very expensive.
Only about 3% of Earth's water is fresh. Two percent of the Earth's water (about 66% of all fresh
water) is in solid form, found in ice caps and glaciers. Because it is frozen and so far away, the fresh water in ice caps
is not available for use by people or plants. That leaves about 1% of all the Earth's water in a form useable to humans and
land animals. This fresh water is found in lakes, rivers, streams, ponds, and in the ground. (A small amount of water is found
as vapor in the atmosphere.)
Water is constantly being cycled between the atmosphere, the ocean and land. This cycling is a
very important process that helps sustain life on Earth.
As the water evaporates, vapors rise and condense into clouds. The clouds move over
the land, and precipitation falls in the form of rain, ice or snow. The water fills streams and rivers, and eventually flows
back into the oceans where evaporation starts the process anew. Learn a lot more about this complicated process in concepts.
Water's state (solid, liquid or gas) is determined mostly by temperature. Although
water continuously changes states from solid to liquid to gas, the amount of water on Earth remains constant. There is as
much water now as there was hundreds of millions of years ago.
