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|Where does your water come from:
According to the US Geological Servey (USGS), the earth contains 326,000,000 cubic miles of water, and over 70% of the earth's surface is covered by water. Although water is abundant on the earth, most of it is unusable for drinking, agriculture, or industry.
As the diagram below shows, only about 0.25% of the water on earth is available for drinking, agriculture, or industry. Nearly 99.75% of the water on earth is either salty (mostly in the oceans) or locked up as ice (mostly in the polar ice caps).
Fresh, water accounts for only about 2% of the world's total water supply, the rest is salt water.
The majority of the fresh water (87%) is locked away as ice in the polar ice caps, continental ice sheets and glaciers.
There are only two sources of fresh water for all individuals in the world, whether they live in the most remote area of the earth or in the middle of New York or Beijing: Surface water and Ground Water.
Surface water, such as rivers and lakes, only accounts for less than 1% of the worlds fresh water reserves. Water in the air, in plants and animals etc., accounts for such as tiny percentage that it has been included in the surface water category.
The rest of the world's fresh water supply, about 12% is groundwater.
Note: on recent checking (5/05) it seems as though
the values described here will need to be updated based on slightly
different values at sites like:
An interesting demonstration might be to fill a gallon of
water which would
represent the total volume of water on the earth and demonstrate the amount of
water in the different categories, particularly that fraction which is available to
human use. You can pour the relative amounts into glasses, measuring cups,
or beakers to actually show how the water is proportioned.
1 gallon = 4 quarts = 128 fluid ounces (floz) = 757 tsp
Based on the figures above
98% = salt water = 125.44 floz = 3.92 quarts
2% = fresh water = 2.56 floz = 15.14 tsp
87% of the 2% is ice = 2.227 floz = 13.17 tsp
12% of the 2% is ground water = 0.307 floz = 1.82 tsp
1% of the 2% is in rivers and lakes = 0.026 floz = 1.54 tsp
The Water Cycle:
This is the so-called
that nearly everyone has studied in school at one time or another.
Groundwater is defined as the water filling spaces between rock particles in special porous rock layers known as 'aquifers'. Perhaps the best way of imaging an aquifer is as a solid sponge. Rainwater trickling down from the ground surface (infiltration) fills the spaces in the rock. When the water is stopped by an impermeable layer of rock underneath the aquifer (a confining layer) the aquifer begins to fill.
Water in an aquifer does not sit still. It flows through the spaces and cracks in the rock, pulled by gravity and pushed by the force of the water above and behind it. The water moves from an area where water enters the aquifer (a recharge zone) to an area where water exits the aquifer (a discharge zone). This movement has the effect of removing a lot of impurities from the water, filtering it through the rock so that groundwater is generally much cleaner than surface water. As groundwater can be very clean, it may require little or no treatment before being used. The level of treatment depends on what it is to be used for. This often makes groundwater a relatively inexpensive source of 'raw water' for public supply.
in the United States:
The USGS Water Science for Schools site has a very interesting graphic showing the Source and use of water in 1995. At first glance it looks a bit messy and hard to understand, but with some study, it is a very complete picture of where water came from and how it was used in 1995.
To give one example, Domestic and Commercial water use (which includes drinking water):
Required 41,600 Million gallons per day or 12.2% of the total water used in the US.
4.8% of the domestic and commercial water used came directly from surface water and was not treated by a public water company before use.
10.3% of the domestic and commercial water used came directly from ground water and was not treated by a water company before use.
The remaining 84.9% of the domestic and commercial used water was treated by a water company before distribution to homes or businesses.
87.9% of the total water treated by water companies was used domestically or commercially, and most of the rest was used by industry.
The Environmental Protection Agency EPA has a Ground Water Primer site you may wish to take a look at. This program is written for community leaders, public water system suppliers and the general public that has an interest in protecting both their water supply and ground water in general.
An excellent site that covers many aspects of Earth's water is hosted by the USGS. The U.S. Geological Survey's (USGS) Water Science for Schools web site offers information on many aspects of water, along with pictures, data, maps, and an interactive center where you can give opinions and test your water knowledge. Although it is targeted at school-age children, the information is very complete and presented in a way that can be enjoyed by anyone.
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