There's a reason for the old axiom, "Water, water, everywhere nor any drop to drink.'' While nearly three-quarters of our planet is covered with water, only 1 percent to 2 percent is usable.

For much of the world, there indeed is not enough for everyone to drink, much less to bathe, do laundry or flush away sewage.

The situation is growing into a crisis of such dimensions that some believe water could become the oil of the 21st century -- a major influence on the economy, a determinant of policy and a possible cause of war.

It is against this backdrop that a national conference was held this week at the Westin Convention Center Hotel focusing on what is known as water quality trading -- a variation of the pollution credits trading that large companies and municipalities engage in. Under pollution credits trading, pollution credits are awarded when a plant or other facility surpasses government guidelines for pollution control. The credits can then be sold to a plant that falls short of the guidelines.

Water quality trading is intended to work much the same way. Formalized by the Environmental Protection Agency in 2003, such trading allows companies and plants confronting high costs to meet water quality regulations for specific watersheds to obtain pollution reductions from other sources of water pollution that are exceeding guidelines in their watershed.

"Trading has the potential to finalize that Roosevelt dream -- to treat our resources as assets, with value, not as a public good with no value," Brian I. Knight, chief of the U.S. Department of Agriculture's Natural Resources Conservation Service, said yesterday as he closed the conference, citing President Teddy Roosevelt's exhortation to treat natural resources as assets.

In areas such as Pittsburgh where water is abundant, it can be difficult to recognize its scarcity worldwide. But the lack of clean water is a leading cause of death in the developing world, said Robert Radke, chief executive officer of US Filter, the Marshall-based water and wastewater treatment company.

"Every eight seconds, a child dies of water-related diseases," Mr. Radke said.

Part of the challenge in dealing with the crisis is engaging people who have not felt its impact.

"Relative to its importance, water is very, very cheap, and is being used in an unconscious way" in the United States, Mr. Radke said.

Water is five times more expensive in Europe than here, and consequently, in places such as his native Germany, "it is being used by consumers in a much more diligent way."

One thing that would make the crisis more real to Americans, he said, would be an increase in water rates -- an increase he said is certain to come within five to 10 years as the demand for water rises, and an increase that Pittsburgh Water and Sewer Authority customers already are feeling as the city moves to upgrade in some cases century-old pipes.

The EPA reports that the country's existing infrastructure for water treatment and delivery will require $500 billion worth of upgrades over the next 20 years. The Allegheny Conference on Community Development has put a $10 billion price tag on upgrading the 11-county region's sewers and water conduits.

Mr. Radke does not expect the money for all those improvements to come from the federal government. "It can only come from taxes or from better rates being paid by consumers," he said.

Water rate increases, like increases in the price of oil, will not only stimulate conservation, Mr. Radke said, but also will spark the development of new technologies.

For example, in California, which has a long history of water problems, the West Basin Municipal Water District has built a facility that recycles wastewater from the Los Angeles Hyperion Wastewater Treatment Plant. Companies such as Chevron and BP use the recycled water rather than fresh water in oil refineries. The facility has thereby saved 65 billion gallons of drinking water.

US Filter, which became part of the German conglomerate Siemens in 2004, is positioned to ride the growth in water demand. Its new affiliation gives it access to 190 countries where Siemens has operations, which has fueled a 50 percent annual growth in US Filter's international business.

While conservation, new technologies and market-based responses such as water quality trading and rate increases may all play a part in dealing with the looming crisis, no single approach will be sufficient, Mr. Radke said.

"It's not an easy fix," he said. "It is a real complex problem and it requires a complex solution."