He stops and studies the water level in his canal. It's rising but still below a stain on the canal's concrete wall, a measuring point that Romo trusts implicitly through experience. In a few minutes, the water reaches the stain, meaning there is sufficient pressure for Romo to crank a rusty metal jack that opens a wooden gate.

"Can lose a finger if you're not careful," he said. With a loud swooosh, a wall of water moves down his canal. For the next several hours, Romo will repeat this ritual again and again, harnessing gravity to shepherd the day's water through his corner of the valley.

Romo is a zanjero -- pronounced sahn-HAIR-o -- Spanish for overseer of the mother ditch. His job is to deliver prescribed amounts of Colorado River water to farmers served by the Imperial Irrigation District in southeastern California. It's a job rich in tradition, one that mirrors the settlement of the West and its complicated relationship with water.

The zanjero was once the most powerful man in any community, entrusted with overseeing its most valuable resource. In early Los Angeles, he was paid more than the mayor. Long before he engineered the city's future, William Mulholland learned the nuances of water working as a zanjero.

"He is the yea and nay of the arid land, the arbiter of fate, the dispenser of good and evil, to be blessed by turns and cursed by turns, and to receive both with the utter unconcern of a small god," said the Century Magazine in New York, describing the job in 1902.

Today, the zanjero is an endangered species, his craft too imprecise, his tools too crude to look after water in a region ravaged by drought.

The Imperial Irrigation District, which provides water to nearly 500,000 acres of farmland in the valley hard against the Mexican border, is among the last to employ zanjeros working the traditional way. More than 100 men labor around the clock controlling the flow of more than a trillion gallons of water a year, largely by hand.

"You learn to appreciate and respect water," said Joe Mariscal, 53, a zanjero for 27 years. "You appreciate what it brings us in terms of food and life. But you respect it because it can do a lot of damage when it's not controlled."

With the Colorado River basin locked in an extended drought that threatens to empty Lake Mead and Lake Powell, the Imperial Valley faces changes that will alter the rhythm of life along canals named Pear and Plum, Dogwood and Daffodil, Eucalyptus and Elder.

Under a 2003 agreement, the irrigation district must eventually transfer 9% of its river allotment to San Diego and the Coachella Valley. Limitations and the sudden need to conserve have shaken an area where water was once considered inexhaustible.

Signs of change already abound. Fields lie fallow. Giant earthmovers march across the desert, replacing a 23-mile segment of the All-American Canal -- the valley's link with the Colorado River -- with a concrete-lined channel that will prevent seepage.

With each drop of water needing to be accounted for, an irrigation system that hasn't changed much since the 1950s will increasingly move to remote sensors and automation. For the zanjeros -- who still calculate water flows using a yardstick and were just recently issued mobile phones -- the changes will be profound.

"I love my job. The early morning is exhilarating. The sense of freedom that we can make certain decisions and are in control of something," said Romo, 53, a zanjero for 32 years. "In the future we will act less as a zanjero and more like a technician. . . . It's inevitable."

The Imperial Valley lies below sea level in a gently sloping, ancient lake bed containing rich soils deposited over hundreds of years when the Colorado River flooded.

Without water, the valley is a wasteland. As early as the 1850s, visionaries saw an Eden beneath its crusty surface, but it would be half a century before the first ditches were built. The completion of Hoover Dam and the All-American Canal established the valley as one of the nation's most bountiful agricultural regions. Anything will grow here if it's fed enough water.

A century ago, zanjeros worked the canals on horseback. They were armed; disputes with farmers could turn ugly. A zanjero was nearly inseparable from his canals, tending them day and night and raising his family in an employer-owned ditch-front home that ensured he was never far from work.

The horses, guns and "zanjero houses" are long gone, but the job remains largely the same. It is demanding work. Cranking corroded jacks, opening gates with iron rods, shuffling heavy timbers against the force of moving water, raking out debris -- it adds up to shoulder injuries, bad backs, torn knees.

A few years ago, Andy Curiel was adjusting a gate on a concrete span when it collapsed, dropping him into the rushing water. He hurt his back and was out for a week.