Assured Water Supply Rule Struck Down What It Means for Arizona Contractors

For nearly three years, one three-word phrase has quietly shaped where and how fast new residential subdivisions could move forward across much of the Phoenix metro area: assured water supply. This spring, a Maricopa County Superior Court ruling changed the legal landscape around that requirement, at least for now, and the outcome carries real implications for members building Arizona's next phase of growth.

Here's what the rule actually required, what the court decided, and what contractors and developers should be watching as this continues to play out.

The Background: Arizona's Groundwater Management Act

Arizona's Groundwater Management Act of 1980 established seven Active Management Areas, or AMAs, across the state, including the Phoenix AMA covering most of Maricopa County. The law's purpose has stayed consistent since its passage: reduce reliance on groundwater by encouraging renewable supplies for new growth, protecting the state's long-term water resources rather than depleting them project by project.

Within those AMAs, the Assured Water Supply Program requires developers to demonstrate that a proposed subdivision has access to water that is physically, legally, and continuously available for at least 100 years. For a subdivision of six or more lots outside the service area of a municipal provider with an existing Designation of Assured Water Supply, that means securing a Certificate of Assured Water Supply before the Arizona Department of Real Estate will issue the public report required to sell lots. In practice, this requirement, not zoning alone, has often been the real deciding factor in whether and when a parcel of raw desert land could actually become new rooftops.

The 2023 Model That Changed the Math

In June 2023, the Arizona Department of Water Resources released an updated groundwater model for the Phoenix AMA, incorporating new data on well pumping and basin conditions. The model's finding was significant: over a 100-year horizon, the Phoenix AMA would face an estimated 4.86 million acre-feet of unmet groundwater demand, effectively showing that the area's groundwater is already fully committed to existing and permitted uses.

That finding didn't affect cities, towns, and water providers that already held a Designation of Assured Water Supply, which covers the large majority of established Phoenix-area communities. But for proposed subdivisions outside those service areas, the practical effect was significant: new developments could no longer secure a Certificate of Assured Water Supply based on Phoenix AMA groundwater alone. Builders in that position needed to secure renewable supply instead, Central Arizona Project water, effluent, or other surface water sources, a considerably higher bar for projects on the edge of the metro area's growth footprint.

The Legal Challenge and This Spring's Ruling

The Home Builders Association of Central Arizona, represented by attorneys from the Goldwater Institute, challenged how ADWR implemented what became known as the unmet demand rule, arguing the agency had put the restriction in place without following the formal rulemaking process required under the Arizona Administrative Procedures Act. This spring, Maricopa County Superior Court Judge Scott Blaney agreed, ruling that ADWR lacked the legal authority to implement the unmet demand rule the way it had, since the agency bypassed the proper rulemaking process. The ruling blocked ADWR from continuing to use the unmet demand finding to determine whether developers have sufficient groundwater to meet the 100-year assured supply requirement.

Supporters of the ruling framed it as restoring housing supply and construction activity that the rule had constrained in one of the country's fastest-growing markets. What comes next is still unfolding. A procedural ruling like this one doesn't necessarily resolve the underlying water supply question ADWR's model identified; it addresses how the agency went about implementing a response to it. ADWR retains the option to pursue the same policy goal through a formal rulemaking process that complies with the Administrative Procedures Act, and further appeals in this case remain possible as well.

What This Means for Members Right Now

For contractors and developers with projects that were affected by the unmet demand rule, this ruling may open a path forward for subdivisions that had been stalled or unable to secure a Certificate of Assured Water Supply based on groundwater. That said, the legal and regulatory picture here is genuinely still moving, and members with projects in this position should track developments closely rather than assuming the current situation is permanent. AZAGC will continue to monitor how ADWR responds and whether the ruling is appealed, and will share updates through our advocacy channels as the situation develops.

Why This Connects to Arizona's Broader Growth Story

Water availability sits underneath nearly every major growth story shaping the state's construction pipeline right now. Our coverage of Arizona's data center construction boom and the $2B semiconductor complex planned in Peoria both point to the scale of industrial and technology investment flowing into Arizona, investment that depends on the same water infrastructure and supply questions shaping residential development. Large industrial and residential growth aren't competing for entirely separate resources; they're both drawing on the same regional water picture that the Assured Water Supply Program is designed to manage.

This is also why water infrastructure investment, treatment capacity, delivery systems, and augmentation projects, matters as much as the regulatory question of how supply gets certified. Our article on utility infrastructure planning and why AZAGC's involvement matters for contractors covers the broader infrastructure planning landscape this issue fits into, and water supply planning belongs squarely within that same conversation about how the state builds capacity to support continued growth.

Renewable Supply Still Matters Regardless of the Ruling's Outcome

Whatever happens with this specific rule going forward, the underlying dynamic driving it, growing demand against a groundwater resource that Arizona's own regulatory framework was designed to protect from over-reliance, hasn't gone away. Projects that can secure renewable water supply, through CAP allocation, effluent reuse, or other surface water sources, remain in a stronger long-term position than those depending solely on groundwater in an AMA where the state's own modeling shows that supply is already fully committed.

For members planning projects with multi-year timelines, this is worth factoring into site selection and water planning now, independent of how the current legal situation resolves. The regulatory mechanism may be in flux, but the resource constraint the mechanism was built to address is not.

How This Fits Alongside Arizona's Transportation and Infrastructure Investment

Water isn't the only resource question shaping where and how Arizona builds next. Our coverage of the fully funded 20-year RTA plan reflects the same long-horizon infrastructure planning mindset that water supply questions demand, decisions made now that shape the built environment for decades. Transportation capacity and water capacity both function as gating factors for growth, and both require the kind of sustained regulatory and policy engagement that keeps pace with a state adding residents and industry as quickly as Arizona has been.

The parallel is worth drawing out clearly. A well-funded transportation plan means little if water supply constraints stall the housing and industrial development that plan is meant to serve, and expanded water capacity means little if the roads, utilities, and infrastructure needed to actually build on newly available land aren't keeping pace either. These pieces move together, which is part of why AZAGC tracks developments across water, transportation, and utility infrastructure as connected parts of the same broader growth picture rather than isolated issues.

What to Watch Next

Members with projects potentially affected by this ruling should watch for whether ADWR appeals the decision, whether the agency initiates a new, formal rulemaking process to pursue the same unmet demand policy through the correct procedural channel, and how water providers and municipalities in the Phoenix AMA respond in the interim. AZAGC will continue tracking this issue and sharing updates as the legal and regulatory picture develops further.

Final Thoughts

Water supply and construction growth in Arizona are more tightly linked than many outside the industry realize, and this spring's ruling is a reminder of just how much regulatory detail sits underneath a question as fundamental as whether a project can move forward at all. Whatever the ultimate resolution, staying informed on how this plays out, and factoring long-term water supply strategy into project planning regardless of the current legal status, remains one of the more important things members can do as Arizona's growth continues.