Groundwater modeling prompts halt of new assured water supply certificates for Phoenix area subdivisions

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June 6, 2023 — Recent research indicates that the rapidly expanding Phoenix region will face a significant water shortage within the next 100 years unless new water sources are found. A groundwater model released by the Arizona Department of Water Resources Opens in a new tab.reveals an expected shortage of nearly 5 million acre-feet of groundwater for the future population of the Phoenix Active Management Area, resulting in an urgent call for alternative resources.

The model area combines the Lower Hassayampa, West Salt River Valley, and East Salt River Valley sub-basins; and includes portions of the Maricopa-Stanfield, Lake Pleasant, and Eloy sub-basins. The Phoenix AMA model replaces the existing Salt River Valley and Lower Hassayampa sub-basin groundwater models.

In response to the impending water scarcity, the state has decided to halt the approval of new assured water supply certificates. These certificates, necessary for any subdivision of six or more lots, prove the development can sustain a water supply for 100 years. This temporary hold is aimed at preventing further depletion or over-allocation of groundwater in the Phoenix Valley. However, Governor Hobbs reassured citizens that growth within major cities will not be affected dueOpens in a new tab. to their robust water portfolios.

What is a 100-Year Assured Water Supply Certificate?

According to the Arizona Department of Water ResourcesOpens in a new tab., an “assured water supply determination is required to obtain a public report from the Arizona Department of Real Estate to sell or lease (for more than one year) lots within a subdivision that are located within an Active Management Area (AMA). The assured water supply requirement can be met with a written commitment of service from a water provider designated as having an assured supply, or by obtaining a Certificate of Assured Water Supply.

Assured water supply requirements apply inside the AMAs. Adequate water supply requirements, meanwhile, apply outside the AMAs. The Adequate Water Supply Program serves primarily as a consumer advisory measure to inform home buyers about the adequacy or inadequacy of the water supply. Inside the AMAs, the Assured Water Supply program requires developers to demonstrate an assured water supply prior to selling lots. The Assured Water Supply requirements are designed to protect and preserve groundwater supplies in the AMAs as well as to ensure sufficient water supplies for new development.

To obtain an adequate water supply determination, the water supply must meet the following requirements: (1) the water supply must be physically available; (2) the water supply must be continuously available; (3) the water supply must be legally available; (4) financial capability to construct the water delivery system and any storage or treatment works must be demonstrated; and (5) the water supply must meet applicable water quality standards. Outside of the AMAs, developers can sell lots to homebuyers with an inadequacy determination from the Arizona Department of Water Resources (ADWR), unless the subdivision is located in a mandatory adequacy jurisdiction.

Inside the AMAs, where the Assured Water Supply requirement applies, the above five requirements must be met in addition to the following two: (1) groundwater use must be consistent with the management plan for the AMA; and (2) groundwater use must be consistent with the management goal of the AMA.”

Impact on Housing Growth and City Development.

This halt on water applications may slow housing growth, particularly for homebuilders planning large developments in areas that have not yet secured a certificate. For instance, the development of thousands of homes in west Buckeye might face difficulties without other water supplies. Alternatively, this could lead to more rental communities since they, alongside most commercial developments, are not obliged to obtain an assured water supply certificate.

Notably, Queen Creek and Buckeye, unlike most cities in the Valley, lack assured water supply designations.Opens in a new tab. They have been striving to increase their water portfolios for several years. Amidst concerns of unmet groundwater demand, state and local leaders maintain their objective of attracting businesses and residents to Arizona.

Conservation Plans and Future Growth.

Given the circumstances, many cities have initiated conservation plans, exercising caution in approving economic development projects based on benefits and water demand. A new study from the Bureau of ReclamationOpens in a new tab. shows that the entire West Valley, which heavily relies on groundwater, could face an unmet demand of up to 260,000 acre-feet of groundwater by 2060.

In light of these findings, Governor Hobbs announced an allocation of $40 million in federal American Rescue Plan Act dollars to fund water conservation and improve water infrastructure. The Arizona Water Resiliency Fund will be managed by the Department of Water Resources, promoting sustainable groundwater management through grants and financial support.

Phoenix’s Proactive Measures.

In a separate initiative, the city of Phoenix agreed to voluntarily forego up to 50,000 acre-feet of its Colorado River entitlement per year for a $20 million return in 2023, and potentially more in the future. Cities like Phoenix, which have amassed a surplus of water supplies over decades, may not be as impacted by the halt in certificates of assured water supply compared to cities primarily reliant on groundwater.

The Future of Water Security in Arizona.

The Phoenix metropolitan area, with its burgeoning population, faces significant water challenges due to its increasing reliance on depleting groundwater wells. This issue is amplified by the impacts of climate change, prompting drastic measures to conserve and manage water resources.

However, Arizona’s steps to restrict construction of new homes dependent on groundwater wells are a crucial part of confronting these problems. This action not only ensures the security of water but also signals the need to reconsider land development strategies, emphasizing sustainable growth over unchecked expansion. The road ahead may be challenging, but it is the necessary path towards long-term water security in the region.


Since 1995, Deborah has owned and operated LegalTech LLC with a focus on water rights. Before moving to Arizona in 1986, she worked as a quality control analyst for Honeywell and in commercial real estate, both in Texas. She learned about Arizona's water rights from the late and great attorney Michael Brophy of Ryley, Carlock & Applewhite. Her side interests are writing (and reading), Wordpress programming and much more.

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