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One resource, though, remains virtually uncontaminated even though some 800,000 people use it daily. Lying below 1.26 million acres of east-central Illinois is some of the cleanest water in the nation. A group of scientists and public leaders from central Illinois are trying to keep it that way.

Sipping Ancient Water

The Mahomet Aquifer undergirds east-central Illinois, from just north of Danville at the Illinois-Indiana border westward to the southeastern corner of Tazewell County near Peoria. Across this nine-county span, it ranges in width from 8 to 18 miles and is buried 100 to 200 feet below the surface. Some four trillion gallons of water are in the aquifer. That's enough water to fill a lake the size of the City of Chicago to an average depth of 83 feet.

Though sizable, the aquifer is tiny in comparison with some of Illinois' surface-water sources. Lake Michigan, tapped for water by the 9 million residents of Chicago and its surrounding suburbs, contains 300 to 400 times more water. The volume of water flowing past St. Louis in the Mississippi River every two and a half weeks is equal to the entire volume of water flowing through the Mahomet Aquifer.

In its purity, though, the Mahomet Aquifer surpasses these and nearly every water source in Illinois and beyond. Drink a glass of tap water from the aquifer and you're drinking water that fell on earth between 3,000 and 10,000 years ago, well before pesticides, petroleum-based fuels, or industrial pollutants made their appearance. This "fossil" water is free of harmful bacteria and pollutants. To find cleaner water, you'd have to melt ice from deep within an Arctic glacier.