The world is facing a worsening shortage of clean, usable water. In this third of four reports on the global water crisis, VOA's Rosanne Skirble examines a major cause of the problem in the United States the over-pumping of once-abundant reservoirs of underground water.

Consider these facts about U.S. water use: The United States is among the largest irrigators in the world, behind only China, India and Pakistan. Two-thirds of the water used on America's farms is taken from underground sources. Over half the American population relies on aquifers for drinking water.

Over-pumping of groundwater for agriculture, industry or domestic use comes at a steep ecological price. It disrupts the natural hydrologic cycle, causes rivers and wetlands to dry up, the ground to collapse and fish and wildlife and trees to die.

These adverse impacts are the focus of University of Arizona law professor Robert Glennon's new book: Water Follies: Groundwater Pumping and the Fate of American's Fresh Waters. "The first problem is that we have not recognized that ground water pumping is an environmental disaster. And, that's why I why I wrote the book," said Prof. Glennon. "We have done things hastily without reflection, and we need to take a look at how we use our water resources."

Robert Glennon says the root of the problem is that many Americans take water for granted. "We perceive water as something that is there when you turn on the tap. At the end of the month, if we receive a bill, and some people don't, it is a relatively small amount," he says. "In the United States we have profoundly undervalued this life-sustaining resource. We use an immense quantity to grow very low-value crops such as alfalfa or cotton, particularly in areas in the West when these crops grow perfectly well elsewhere without the need of irrigation."

Water Follies details the environmental impact of various water projects around the United States. We learn about the extravagant irrigation of potato fields from underground aquifers in Minnesota so that farmers can harvest a crop that will produce french fries of the same size and shape.

We learn how San Antonio, Texas, has revitalized its downtown by pumping groundwater into a dry riverbed to sustain Riverwalk, a four-kilometer tourist attraction. And we learn the story behind a top-selling supermarket product in the United States: bottled water.

The problem, Robert Glennon says, is that government regulators allow the sale of water designated as "spring" water only if the well that pumps the water is located immediately adjacent to a natural spring. "If you put a well next to a spring, you are going to diminish the flow in the spring. I use this in the book to try to get people's attention because this is something that we American consumers will get," he says. "We see bottled water is being used. And if something that innocent can have an environmental impact, what about all the other uses that we have? What about our sprawling laws, in-ground pools, farming or mining use around the country?"

Robert Glennon says bottled water is literally a drop in the bucket compared with other water use problems in the United States. "If you are looking at the bigger picture, how much water are we using to grow low-value crops and in part this simply because the water is for the taking," he says. "We have no charge for water in most sections across the United States. It costs very little, and we are using it in extravagant ways. That has to change. We need to begin to price water appropriately. That appropriate price must include consideration of the environment."

Water Follies also proposes a ban on locating wells next to rivers, lakes and springs, a conservation measure that discourages waste. And the book envisions a combination of financial incentives and government policies to address the problem in a comprehensive way.

Robert Glennon hopes the book helps to get the issue of groundwater pumping on the national environmental agenda before America's well, literally, runs dry.