What Is a Certificate of Assured Water Supply, and Why Does It Matter When You Buy in Maricopa County, AZ?

If you're buying a home in Maricopa County, there's a good chance nobody has ever mentioned the words "assured water supply" to you — and for most buyers, that's fine, because the water question was already settled decades ago by the city or water company serving the neighborhood. But if you're looking at a newer subdivision, a rural parcel, or a property in one of the county's unincorporated pockets, this is one of those quiet background details that can actually affect whether you can build, whether you can get a loan, and how confident you should feel about turning on the tap ten years from now. In short: an assured water supply (AWS) is Arizona's way of requiring that a subdivision prove it has enough water, legally and physically, to serve homes there for the next 100 years — and where a property falls on that spectrum is worth understanding before you write an offer, not after.

What "Assured Water Supply" Actually Means

Arizona created the Assured Water Supply program decades ago as part of the state's broader effort to manage groundwater in its most populated regions. Within Arizona's Active Management Areas (AMAs) — and most of Maricopa County sits inside the Phoenix AMA — a developer generally has to demonstrate that a subdivision has a water supply that's physically available, legally available, and reliable for the next 100 years before final plats can be recorded or lots can be sold. That demonstration usually takes one of two forms:

• Service from a Designated Provider. If a city, town, or private water company already holds a "Designated Water Provider" status from the Arizona Department of Water Resources (ADWR), a written commitment of service from that provider is generally enough. Most established Maricopa County cities — Phoenix, Mesa, Chandler, Gilbert, Scottsdale, Glendale, Peoria, and others — are Designated Providers, which is why buyers in long-established neighborhoods rarely think about this at all.
• A separate Certificate of Assured Water Supply. If the land isn't served by a Designated Provider, the developer has to go through ADWR directly and obtain (or rely on) a Certificate of Assured Water Supply (CAWS) or an Analysis of Assured Water Supply before the subdivision can be platted and sold.

Either way, the point of the program is the same: nobody should be selling home lots in a groundwater-managed area without first showing there's actually enough water, legally secured, to support those homes for a century.

Why This Matters More in Some Parts of Maricopa County Than Others

Inside City Limits, Served by a Designated Provider

If you're buying an existing home in an incorporated city — say, a resale in Ahwatukee, a townhome in downtown Gilbert, or new construction in a master-planned community built by a national builder inside city limits — the water question was almost certainly resolved when that community was originally platted, often years or decades ago. The city or water utility already carries Designated Provider status, and the builder's original approvals already accounted for water. You still can and should ask, but this is rarely where surprises show up.

Unincorporated Maricopa County and Rural Subdivisions

The picture changes in unincorporated parts of the county — areas that aren't inside any city or town boundary and rely on private wells, small water companies, or hauled water rather than a municipal system. Some of these areas have gained real attention in recent years precisely because they sit outside a Designated Provider's service area, which means new development there faces a higher bar: either the landowner secures a Certificate of Assured Water Supply directly from ADWR, or the lots are sold with disclosures that make clear no such certificate exists and buyers are relying on a private well or hauled water instead. Buyers looking at acreage, off-grid-style properties, or newer subdivisions on the edges of the Valley should treat this as a standard due-diligence item, not an afterthought.

How to Check Before You Buy

You don't need to become a hydrologist to buy responsibly in Maricopa County — you just need to ask the right questions at the right time.

1. Ask who provides water to the property, and confirm it in writing. Your purchase contract and the seller's property disclosure should identify whether the home is on a municipal water system, a private water company, a shared well, or an individual well.
2. If it's a well, ask about well-sharing agreements and water levels. Shared wells come with legal agreements that govern maintenance costs and usage — get a copy and have your agent or attorney review it.
3. For new construction or a subdivision built in the last few years, ask your agent or the builder whether the community has a Certificate of Assured Water Supply or is served by a Designated Provider. This information is a matter of public record through ADWR and can be verified independently.
4. Loop in your title company. Title companies working in Maricopa County routinely handle properties with water company easements, well-sharing agreements, and CAWS documentation, and can flag anything unusual in the title report before you close.
5. For rural or unincorporated parcels, consider a well inspection as part of your due diligence period, the same way you'd order a home inspection or a termite report.

Common Mistakes Buyers Make

The biggest mistake is simply assuming that because a home has water running through the pipes today, that automatically means the long-term supply is secure and documented — those are two different things. A second common mistake is skipping the disclosure paperwork on rural properties because the buyer is excited about the acreage or the view, only to discover during escrow that the well needs work or that no assured supply documentation exists for that parcel. A third is assuming every part of Maricopa County works the same way; the reality is that water arrangements can look completely different from one side of a city boundary to the other, even on properties just a mile or two apart.

Two Realistic Scenarios

Scenario one: the straightforward resale. A family is buying an existing home in a well-established Glendale neighborhood built in the 1990s. Water comes from the City of Glendale, a longtime Designated Provider. There's nothing unusual to investigate here beyond normal disclosures — the water question was settled long before this family ever looked at the listing.

Scenario two: the rural parcel. A buyer falls in love with a few acres in an unincorporated part of the county, picturing space for horses and room to spread out. The property is on a private well, and there's no Designated Provider serving that area. Before writing an offer, the buyer's agent helps them pull the well's history, ask the seller for water usage and maintenance records, and confirm whether any CAWS documentation exists for that subdivision. It turns out the well is older and hasn't been tested recently — so the buyer negotiates a well inspection contingency and a water quality test as part of the contract, rather than finding out after closing.

Frequently Asked Questions

Does every home in Maricopa County need a Certificate of Assured Water Supply?

No. Homes served by a Designated Water Provider — which covers most established cities and towns in the county — don't need an individual certificate. The certificate requirement applies mainly to new subdivisions outside a Designated Provider's service area.

How do I find out if my water provider is a Designated Provider?

The Arizona Department of Water Resources maintains a public list of Designated Water Providers. Your real estate agent or title company can also help you confirm this for a specific address.

Is buying a home on a private well automatically risky?

Not automatically — plenty of Maricopa County residents live happily on private wells for years. It just means the due diligence looks different: you're checking well depth, production, maintenance history, and water quality instead of relying on a municipal guarantee.

Does this affect my ability to get a mortgage?

It can. Some lenders require a well and septic inspection, or documentation of water availability, before approving a loan on rural or unincorporated properties. It's worth flagging this with your lender early in the process.

Where in Maricopa County is this most likely to come up?

It tends to matter most for unincorporated communities and rural subdivisions on the edges of the Valley, and for newer developments outside existing city water service areas. Established neighborhoods in cities like Phoenix, Mesa, Chandler, Gilbert, Scottsdale, Peoria, and Glendale are almost always covered by a Designated Provider already.

Should I hire someone to research this, or can my agent help?

A knowledgeable local agent can point you toward the right questions and public records, and loop in your title company and, if needed, a well inspector — you don't have to figure this out alone.

Bottom Line

For most buyers in Maricopa County, water supply is a non-issue you'll barely think about because it was resolved long before the home was ever listed. But if you're looking at rural land, an unincorporated area, or a newer subdivision outside an established city's service area, it's worth a few extra questions before you get too attached to a property. Stephanie Pondevie is a bilingual REALTOR® in Maricopa County, AZ, helping buyers navigate exactly this kind of due diligence — from confirming who provides water to a property to knowing when a well inspection or a call to ADWR is worth the extra step. If you're weighing a purchase anywhere in Maricopa County and want a second set of eyes on the water question or any other part of the process, reach out through yourhomecomesfirst.com — Stephanie and her team are happy to help you buy with confidence.