|Spaulding and Namowitz, Heath Earth Science. New York: Heath, 1994: 148.||"By one estimate, the amount of groundwater is 50 times as much as all the water in the rivers and lakes."[and see Macmillan below.]||5 × 106 km3|
|The Planet Earth. Chicago: World Book, 1991: 100-101.||"The rocks immediately below the Earth's surface hold over 2 million cubic miles (8 million cubic km) of water-"||8 × 106 km3|
|Groundwater Basics. The Groundwater Foundation. April 2000.||"More than 2 million cubic miles of freshwater is stored in the earth, and half of that is with in a half a mile of the surface."||8.3 × 106 km3|
|Water Supply of the World. Infoplease Kid's Almanac.||"Water Source; groundwater; Water volume, in cubic miles; 2,000,000; Percent of total water; 0.61%"||8.3 × 106 km3|
|"Earth's Freshwaters." Macmillan Encyclopedia of Earth Sciences. New York: Simon & Schuster, 1996: 230.||
|8.2 × 106 km3|
Groundwater is essential to the existence of all life, in particular humans. Although many don't realize, much of the water used in our bathrooms and kitchens and consumed by people is groundwater.
When it rains, water flows continuously. It flows into the rivers, lakes, oceans; is absorbed by plant life; evaporates into the atmosphere; and is absorbed into the ground and into underground rocks. The water that seeps into cracks, and spaces in the soil, sand and porous underground rocks is called groundwater or underground water.
Following the water's absorption into the ground, it enters the aeration, unsaturated, or vadose zones. It is in this region that the pores of the underground rocks are filled with both water and air. This rock contains three levels. The first is the capillary fringe. Water rises just above its boundary, the water table, through capillary action. The second layer, which is found above the capillary fringe, is a region that is always dry unless it rains. The third layer, which can be located above the second region, but below the soil surface, is a film of capillary water that sticks to the grains of the topsoil.
Next, the water must pass through a boundary called the water table. Following this boundary, the water enters the saturation zone. It is in this zone, that water fills up all the open spaces that may exist. The saturation zone stores the water in soil, sand and rocks who are referred to as aquifers. Aquifer is also the name given to porous and permeable rocks that are found beneath the earth's surface.
The water table changes all the time as a result of an area's weather and topography. This makes it extremely difficult to determine the volume of the groundwater of the earth. This accounts for the variation between sources. From the sources used in this research, the volume of the earth's groundwater has been found to range between 2,443,000 and 8,200,000 km3.
In order to determine the volume of the earth's groundwater for the first result, I needed to refer to "Earth's Freshwaters" chart. The volume of the earth's rivers and freshwater lakes were found on this chart, enabling me to find an approximation of the earth's groundwater, since the first source stated that this quantity is fifty times the sum of the volume of all the earth's rivers and lakes. I found the total volume of the earth's rivers and lakes, and then multiplied this sum by fifty, to find an estimate value of the volume of the earth's groundwater.
Vanessa Ballenas -- 2000