Twenty years ago, in October 2003, water officials from across the Southwest signed the largest water conservation-and-transfer agreement in U.S. history, the QSA, or Quantification Settlement Agreement. The agreement has provided 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.