Twenty years ago this week, water officials from across the Southwest signed the largest water conservation-and-transfer agreement in U.S. history, providing decades of water security for San Diego County and benefits for numerous partners across the Southwest. In total, that pact supplies more than half of the water that sustains San Diego County’s 3.3 million residents and $268 billion economy.

The 2003 Quantification Settlement Agreement, better known as the QSA, provides more than 30 million acre-feet of high-priority conserved water to the San Diego region over multiple decades. It helped stabilize demands on the Colorado River and reduced California’s overdependence on surplus supplies. The historic set of more than 20 agreements resulted from years of negotiations between the San Diego County Water Authority, Coachella Valley Water District, Imperial Irrigation District, Metropolitan Water District of Southern California, State of California, and the U.S. Department of the Interior that culminated in a signing ceremony at Hoover Dam.

“This landmark water deal has stood the test of time, providing numerous benefits both in the San Diego region and more broadly across the Southwest,” said Mel Katz, chair of the Water Authority Board of Directors. “One of its most important accomplishments is that it brought water agencies together as collaborators. We’ve had disagreements along the way, but history has validated the value of our collective efforts to provide water security.”