Although 70 percent of the Earth's surface is covered by water, 97 percent of it is contained in the oceans and is too salty to drink (Cunningham and Saigo, 1992). Therefor, fresh water is a precious resource that in some areas of the world is so scarce, that people will fight wars over it. About 25 percent of the world's fresh water is groundwater. Although groundwater is not as accessible as surface water (lakes, rivers and streams), people are willing to dig wells to obtain it in areas where the climate is too dry to allow much surface wa ....