"I have the most satisfying job in Juárez," says Arturo Chávez. He drives what the locals call a pipa, or water pipe. For poor Mexican neighborhoods like Anapra, a desert slum of 5,000 families with no water or sewer lines, tanker trucks like Chávez's are the only source of water clean enough for drinking and bathing. So when pipa No. 415 pulls up over the dunes, it's a community event: families emerge from their shanties as if to greet a rich uncle bearing gifts. Chávez pumps 500 gal. of free water into concrete cubes called pilas, which, say residents, can also mean the "batteries" that recharge their lives.

Not even the pipa, however, could save seven-month-old Antonio García, who choked to death in Anapra this spring. The slum's sallow air had filled his tiny lungs with dust and disease. Dr. Gusta"o Martínez, director of a private Juárez hospital, watched helplessly as the infant writhed in pain before he finally suffocated. "You don't ever forget the face of a seven-month-old who doesn't want to live anymore," he says. When Martínez went afterward to see the family, he found their one-room shanty, built of pallets and cardboard, open on all sides to the wind. Dust swirled around the empty crib in the corner. "I just leaned against the wall and thought, 'I can't compete against this,'" he said.

Juárez is the migration story that most Americans don't hear about: the one that stops just short of the border and grows and grows. The Juárez­El Paso population of 2 million makes up the largest border community anywhere in the world, expanding more than 5% a year. It is a big, wild experiment in what happens when two halves of a metropolis are governed by very different economic, civic and cultural rules. This is a place where two cities breathe the same air, drink the same water and share the same destiny along what U.S. Congressman Silvestre Reyes calls a "seamless border."

El Paso and Juárez offer a test to all the high-minded globalists who think that if you fix the economy, the other solutions will fall into line. On the one hand, manufacturers from Ireland to Japan are streaming into town. Some 400 maquiladoras, or assembly plants, have all but eliminated unemployment in Juárez and have sown the seeds of a stable middle class, "not Mexicans with sombreros," says Miguel Angel Girón, 26, an accountant at an auto-parts factory. But all the problems that booming trade creates are concentrated here as well; the potable water in the cities' common aquifer is set to run out in 25 years; the air quality is imperiled; diseases are spreading, and they don't stop at the customs station. Presidents Fox and Bush talk a lot about working together to find solutions. But at the moment, the most creative efforts come from local officials, the private sector, the charities and community groups that build informal alliances across the river. And they often do it without help from Mexico City or Washington, whose NAFTA dreams created the problems.

Juárez, once a dusty border mountain pass, is now Mexico's fourth largest city, with a population of 1.3 million and 50,000 more arriving each year. Huge clusters of tiny workers' houses rise out of the sand and stretch in every direction. "It's instant urbanization," says Nestor Valencia, who directed El Paso's city planning for 11 years. "One year it's a desert. The next it's a city."

Juárez and its outskirts are dotted with enormous new plants, but these are not your padre's maquiladoras: some look like Italianate palaces (Johnson & Johnson) or works of modern art (Thomson electronics). Some have in-house banks, cafeterias, spic-and-span bathrooms and, increasingly, on-site training in new technologies unfamiliar to illiterate peasants from Oaxaca. Jaime García, 31, an engineer from Torreón, heads an all-Mexican team of 16 young designers at Delphi Automoti"e Systems' Technical Center, working on steering-column prototypes for U.S. cars due out in 2004. From his wide-windowed floor, García has a panoramic view of both cities. He admits that the border isn't Silicon Valley. "But we can see that kind of future from here," he insists. "We're not just assembling things anymore. We're creating things."

Unfortunately life has not changed for everyone in Juárez: hourly pay is still about $1.25. Many workers have to travel hours each way by bus from colonias like Anapra, subdivisions that have sprung up without paved roads, water or sewer service. The homes look like preschool art projects, glued and stapled together from cardboard and plywood and tin. Bootleg power lines drop from overhead wires, loop down to the ground and are held in place by a rock, then snake through the sand to a house. Some wires are live, and arc and spit when it rains. The young women who live here are favored by the maquila bosses for their nimble fingers and obedience. But more than 200 women, many of them maquila workers, have been murdered since 1993 — often raped, strangled and mutilated during their long, dark treks home to remote colonias. Most large maquilas have begun providing bus service, but it has failed to stop the killings.