CIUDAD JUAREZ, MEXICO — JAIME BERMUDEZ boils down the future prosperity and tranquillity of the US-Mexico border to one word: water.
''We've talked about water on this border for 20 years, but nothing has been done,'' says Mr. Bermudez, who, as the father of Mexico's maquiladora industry, has done as much as anyone to create the border's economic boom. ''Now we're at the end of the line.''
Maquiladoras, the duty-free industrial plants that assemble mostly foreign components for re-export using low-cost Mexican labor, use a lot of water, especially as they become more sophisticated and involve electronics. Today 3,000 of them operate in Mexico.
But they are just one part of the border's water challenge as demand booms in what is essentially a semiarid climate.
Nearly 10 million people live in the immediate border region today, where barely 100,000 lived in 1900.
On the American side, water use has skyrocketed as newcomers with profligate water-use habits move in.
The region's aquifers face depletion while its rivers, including the Rio Grande, are confronted with overuse and pollution.
The Rio Grande - called the Rio Bravo in Mexico - is a primary water source for millions of people in Texas, New Mexico, and four Mexican states. On the western end of the border, the Colorado River is a lifeline to parts of Colorado, Arizona, Nevada, and California, although little is left by the time it crosses into Mexico.
In 1973, a US National Security Council report singled out water as the most important issue confronting US-Mexico relations after 2000. Either the problem would be solved on the border, experts agreed, or it would blow up there.
Despite this early warning, and even after water became a high-profile issue in Middle East peace talks, the US-Mexico border water problem has failed to generate intense public concern.
Thomas Vaughn, a researcher at the Rio Grande International Study Center at Texas A&M International University in Laredo, imagines a future when Mexico, frustrated by worsening droughts, builds new dams on tributaries to the Rio Grande. The river flow would be severely reduced or halted, ''but the US has 800,000 people down river who depend on that flow,'' he says. An international conflict that seems unimaginable today could arise. ''In the future, wars are probably going to be fought over water,'' Mr. Vaughn adds. ''Who can say it won't happen here?''
''Water already is a serious source of conflict on the border, and we can be sure that will intensify,'' says Helen Ingram, director of the Udall Center for Studies in Public Policy at the University of Arizona in Tucson and an expert on border resources. ''We'd already have a lot more trouble with it if Mexico had more political power,'' she adds. ''As the enormous inequities [in supply and use] fester, as the population grows, and especially at the point where Mexico gets any leverage, we're going to hear about it.''
What federal attention water resources did get from the US generally came from engineers, Ms. Ingram says. ''It's been either ditch it or dam it, but certainly not sustainable management,'' she says. The International Boundary Water Commission in El Paso, Texas, and a 1944 accord on the Colorado River apportion surface water. But critics say the provisions are out of date. And no one regulates access to the underground aquifers that cities like El Paso, Juarez, and the twin cities of Nogales, Mexico, and Nogales, Ariz., are pumping dry.
One reason for the lack of a tough approach is that ''traditionally, water rights are states' rights,'' says Richard Bath, a border resources expert at the University of Texas at El Paso. That has led to ''water wars'' between US states, with fresh conflicts every time the idea of tinkering with water deliveries arises.
The typical conflict involves disputes between urban and agricultural users. Population growth on both sides of the border outstrips the national average, making such conflicts likely to multiply. One new battle pits California and Las Vegas, Nev., against Arizona over Colorado River water. On the Mexican side, a rural-urban water-use conflict flared up in January between the states of Tamaulipas and Nuevo Leon.
Last summer, officials and residents of Mexico's northeastern states, caught in a devastating drought, were outraged when Texas Gov. George W. Bush Jr. denied Mexico's requests for water assistance. Mr. Bush, usually a strong advocate of good relations with Mexico, explained that the water simply was not his to send south.
Water use, especially in the US, is equated with economic development, Mr. Bath notes. ''The more you use, the better off you're thought to be,'' he says.
Per-capita daily water use in El Paso is 210 gallons - half of it for keeping lawns green and running air conditioners - compared with just 70 gallons across the Rio Grande in Ciudad Juarez. Some US border cities do better - Tucson, Ariz., uses about 150 gallons per person per day - but others are worse. ''Las Vegas, like the rest of us in the middle of a desert, uses an obscene 340 gallons per capita,'' Bath says.
The challenge of water use is going to force a new approach - either through foresight or conflicts, experts say. ''If anything is going to convince us that the border is one region with one destiny to be jointly managed, it will be resources. And among them water,'' Ingram says.
She and other experts see some hope in the emphasis the North American Free Trade Agreement puts on environmental issues. Ingram points to the Border Environment Cooperation Commission, which arose out of NAFTA, as the kind of binational institution that can address water issues - quantity and quality - while there's still time.
''The situation's rife with problems,'' she says, ''but it's not hopeless.''
Others are less optimistic. Mexico's preoccupation with its economic problems and Washington's swing toward equating the border with illegal immigration and drug trafficking are taking the wind out of the sails of cooperation, Bath says.
The border, an American writer said in the 1920s, is a land of ''sunshine, adobe, and silence.'' Today the border is a ''binational living space,'' says Lawrence Herzog, a border scholar at San Diego State University.
The border is also a metaphor for US-Mexico relations, he adds. How the two countries approach problems like water will determine how two different but inextricably linked neighbors get along, and whether they are able to prosper together.