Assured water supply in Arizona is a state test, run by the Arizona Department of Water Resources (ADWR), that asks one question: can a new subdivision prove it has a 100-year water supply? Inside an Active Management Area (AMA), a developer must pass it before recording a plat or selling lots. Without it, the Arizona Department of Real Estate will not issue the public report that allows lot sales.
What the program actually requires
ADWR describes the Assured Water Supply program as one of two programs built to deal with limited groundwater. It looks at current and committed demand, growth projections and the supply behind them, and it asks whether the water will be there for 100 years.
Under A.R.S. 45-576, a person offering subdivided land in an AMA generally needs a certificate of assured water supply from ADWR before presenting the plat to the city, town or county, and before filing a notice of intention with the state real estate commissioner. The statute defines the term in plain language: water continuously available for at least 100 years, consistent with the AMA's management plan and goals, with a showing of financial capability to build the water facilities.
ADWR breaks the test into seven criteria:
- Physical availability of the water (A.A.C. R12-15-716).
- Continuous availability for the 100-year period, or sufficient backup.
- Legal availability, meaning the applicant can prove rights to every supply it counts (R12-15-718).
- Water quality that meets standards after treatment (R12-15-719).
- Financial capability to build delivery, storage and treatment systems (R12-15-720).
- Consistency with the management plan, which sets municipal conservation requirements (R12-15-721).
- Consistency with the management goal of the AMA (R12-15-722).
Certificate or designated provider
There are two ways to satisfy the requirement. A developer can apply for a certificate for the specific subdivision. Or the developer can buy water service from a provider that ADWR has already designated as having an assured supply. In that case no separate determination is needed. A written commitment of service from the designated provider is enough, and A.R.S. 45-576(F) exempts subdividers served by a designated city, town or private water company from getting their own certificate.
For a landowner this is the first fork in the road. A parcel inside a designated provider's service area has a water path. A parcel that needs its own certificate has to prove the water from scratch.
Where the AMAs are
ADWR lists eight AMAs: Prescott, Phoenix, Pinal, Tucson, Santa Cruz, Douglas, Willcox and Ranegras Plain. They cover parts of Cochise, Graham, Maricopa, Pima, Pinal, Santa Cruz and Yavapai counties, per ADWR's program page. ADWR's AMA page says the primary goal in Phoenix, Prescott and Tucson is safe-yield, meaning groundwater withdrawals no longer exceed annual replenishment. ADWR's pages do not spell out how the requirement applies in the newest AMAs, so confirm that with ADWR for any parcel there.
The 2023 Phoenix AMA groundwater model
In June 2023, ADWR released a groundwater model for the Phoenix AMA. It projected 4.86 million acre-feet of unmet groundwater demand over 100 years, meaning simulated wells run dry. ADWR said it would not approve new groundwater-based assured water supply determinations in the Phoenix AMA. Developers and communities would have to use other water sources.
ADWR also said development within existing certificates and designations of assured water supply could continue. The statute itself did not change.
ADWR released an updated model in November 2024 and encouraged applicants to use it. ADWR said that update does not support issuing groundwater-based determinations. It also reported that depth-to-water readings over 1,000 feet still occur in the model. In 2026 it released "Version 3," which refreshes the data and the 100-year projection. ADWR's page says Version 3 is not a recalibration of the 2023 model, and it does not say whether the 2023 policy has changed.
The practical effect: in the Phoenix AMA, a parcel outside a designated provider's service area cannot get a new certificate by pointing at local groundwater. The water has to come from somewhere else.
The alternative path (ADAWS)
ADWR adopted rules in 2024 for an Alternative Designation of a 100-Year Assured Water Supply. The Arizona Capitol Times reported on October 10, 2025 that EPCOR Utilities received the first one, which allows residential construction to resume in parts of the West Valley after a two-year pause. The key condition is that the provider must show supply across its entire service area, not only at the development site.
The same report said ADWR was defending two lawsuits filed by the Home Builders Association of Central Arizona. One argues ADWR lacked the authority to create the alternative path. The other challenges the groundwater modeling requirements. Check the current status of both before relying on this path for a deal.
Outside an AMA: adequate water supply
Most of Arizona's land sits outside an AMA, and the rule is different. Under A.R.S. 45-108, a developer of a subdivision outside an AMA, including dry-lot subdivisions of any lot size, must submit a water supply plan to ADWR before the plat is recorded. ADWR issues a report and sends it to the real estate commissioner and the platting authority.
The statute defines an "adequate" supply as sufficient, of adequate quality, and continuously, legally and physically available for at least 100 years, with financial capability to build the delivery, storage and treatment facilities. That is the first five criteria above. The last two, which tie to AMA management plans and goals, do not apply.
The key difference is disclosure rather than a gate. A.R.S. 32-2181 requires an inadequate or missing water supply to be disclosed. If the director finds the supply inadequate, the commissioner requires promotional materials and sales contracts to display the water report. The Department of Real Estate's water guide states it plainly: outside an AMA, water supplies are not assured, and the law requires adequacy or inadequacy to be disclosed to the buyer. Some local governments also require a 100-year adequacy determination, and ADWR keeps a list of those jurisdictions.
Land without a proven supply still has options. The same guide lists drilling a well, a holding tank or cistern, rain harvesting, commercial water hauling, or a stream or water body if the legal right is confirmed. Any source needs filtration to be potable. It also tells buyers to ask ADWR about grandfathered water rights tied to the land.
What this means for a parcel's value
Water decides what a parcel can become. Land with a designated provider next door can support a plat. Land in the Phoenix AMA without one faces a harder, slower route. Land outside an AMA can be platted, but the water report travels with every lot sale.
Three checks belong in any early review:
- Is the parcel inside an AMA? Check ADWR's AMA maps.
- Is it inside a designated provider's service area? ADWR publishes a list of designated providers.
- If neither, what is the plan for water, and who has proven it?
The process after water is covered in our guide to how to subdivide land in Arizona and the wider land entitlement sequence.
These rules and the pending lawsuits change. ADWR and an Arizona water attorney have the final word on any specific parcel.
Selling land that needs this work
Red Dirt Property buys and entitles land across all 15 Arizona counties. It underwrites parcels against its own statewide parcel data and buys as-is, then handles entitlement after closing, with no agent commission on its purchases. A parcel with an unproven water path is the kind of land that work is built for. If you own one, start at selling land to a developer.