The Elusive Concept of an Assured Water Supply: The Role of CAGRD and Replenishment

For nearly 40 years in its most urban areas, Arizona has prohibited the sale of new subdivision lots that lack a 100-year assured water supply. Originally, an assured water supply meant primarily renewable surface water. But in 1993, the Legislature changed course and created a new path to show an assured water supply using groundwater — a non-renewable resource — with the promise that the groundwater would be replenished with surface water acquired after the fact. This report examines how this program — the Central Arizona Groundwater Replenishment District, or CAGRD — has worked over the last quarter-century and its consequences for water management and urban development in Arizona. We conclude that the unexpected popularity of the CAGRD has created serious challenges for good water stewardship and recommend changes in the CAGRD to ensure that homeowners in CAGRD have long-term water sustainability.