The morning of Tuesday, Sept. 27, 2005, brought hints of a classic New Mexico fall, with a forecast high in the 80s and a trace of rain. But in a Wyndham Hotel at the Albuquerque airport, not far from where the rugged buttress of the Sandia Mountains rose into the autumn sky, life was anything but serene. Tensions were rising around a conference table in a rented meeting room, and the catered sandwich platters sat forgotten.

For more than a year, the Southwest’s top water bosses had been shuttling between airport hotels all over the region. Regulators from the seven states that depend on the Colorado River, together with major urban water-agency managers, faced a collective crisis that threatened the water supply of nearly 40 million people and a $1.4 trillion economy: A six-year drought that showed no signs of letting up.

No one at the table that day commanded more attention than Patricia Mulroy. Then 53, Mulroy was the lead negotiator for the state of Nevada and the head of the Southern Nevada Water Authority, the powerful agency that supplies Las Vegas with its water. Partial to pantsuits and shirts with popped collars — a look she picked up from Katharine Hepburn — Mulroy has a crisp, wrinkle-proof bearing and an often unnerving intensity.

For her, the stakes were especially high. Las Vegas’ population was exploding, but the city had rights to less than 2 percent of the river’s water, and that was running out fast. The one resource Mulroy had in abundance was money: In 2005, the Water Authority would rake in more than $363 million.

Inside the Wyndham, negotiations reached an impasse as representatives from Arizona and Colorado locked horns over differing interpretations of a key part of the complex body of law that governs the river. “It just went on and on and on,” says assistant New Mexico Attorney General Steve Farris. “And the longer it went on, you could just see Pat getting angrier and angrier and angrier.”