What is the water cycle?

The water cycle, also known as the hydrologic cycle, involves the cycling of water through the biosphere.  Water naturally exists in 3 forms: solid, liquid, and gas.  Water constantly cycles through these forms while in the atmosphere (as water vapor or condensed as clouds), on the ground (as liquid water or snow), undergound (as groundwater), in the ocean, and as precipitation (rain, snow, sleet, hail, etc.).  Water enters the atmosphere by a process known as evaporation, and then in condensation it forms clouds.  Lastly, through precipitation the water falls back down to earth.  This cycle then repeats itself over and over again. At any given time just .005 percent of the worlds total water supply is moving through the hydrologic cycle. A drop of water will usually spend 9 days in it but, once it falls it can spend anywhere from 40 years (in a glacier) to 40,000 years (in the ocean) before going into the cycle. Every drop of water winds up moving through the hydrologic cycle.



Why is water important?

To many of us water is just water, we take it for granted, yet we fail to realize how important water really is. It is the substance that makes this earth come alive. It is the most precious gift that has ever been bestowed upon us. Coming in either a solid (ice), liquid (water) or a gaseous state (water vapor) it is the most common substance on the earth. It is almost three times as common as every substance (beside water) combined, covering the earth in 336 million cubic miles. However, 97% is seawater, 2% is locked in ice caps and glaciers, and 1% lies too far underground to retrieve. Out of the eye-popping 336 million cubic miles of water that is on the earth only 1/3% is fresh water which we can drink, and 3/4 of this is locked up in the Antartic ice cap. Without this minute percentage of water a human being can only live for 10 days at the longest, for our bodies are 65% water. In other words water is more precious than gold.
As the years pass water is becoming more and more scarce and yet it is in demand more than ever. By the year 2025 it is estimated that over 1/3 of the worlds freshwater will be gone. Already 26 countries, home to 232 million people are considered to be "water-scarce", meaning they don't have 1,000 cubic meters of water for one person for one day. Not only are countries water-scarce but a lot of their drinking water is contaminated. In Haiti, a water-scarce country, one in five Haitians has access to water which is actually safe to drink. Here people will dig in the sand until they reach a pool of seawater which has been filtered by the sand, scoop it up and drink it. Or even some scoop out what they can out of the gutter or a sewage canal.

Interesting facts about water

• Water is the only substance on earth which comes in three different forms; liquid, solid and a gas.
• Ice is actually less dense than water, that is why icebergs float on water.
• Water has the highest surface tension of all liquids. Because water can form a "skin" precipitation is possible.
• There is no force which exists that can compress water. Meaning nothing could press water into an ice cube.
• Water is the "universal solvent". It dissolves more substances than any other liquid.
• Over 36,000 dams have been built to provide hydroelectric power, drinking water, irrigation, industrial supplies and control floods.
• 1.2 billion people are at risk from drinking contaminated water.
• If 4% of the world's military expenditures (36 billion dollars) was saved each year, all of humanity would have clean drinking water and a sanitary way of disposing waste.
• The Hydrologic cycle in one day uses more energy than the humankind has created throughout it's entire history.
• Our blood is 83% water, the wettest part of our body.
• Our tooth enamel is the driest part of our body at 2% water.
• The largest freshwater lake in the world and the oldest at 30 million years, Russia's Lake Baikal (5,712 feet deep, 812 billion cubic feet) supports 60% of species that occur nowhere else on earth, the highest proportion anywhere.

How have we interfered with the water cycle?
We interfere with the water cycle by taking away huge amounts of freshwater and depleting other water supplies.  By clearing vegetation from land to build roads, parking lots, etc., water cannot seep into the ground to be stored in the aquifer.  Because of this, the water remains on the surface and increases the likelihood of flash floods and surface run-off.  This can cause soil run-off and damages buildings.

Information provided by: http://library.thinkquest.org