Arizona Wastewater Treatment Plants

1. Introduction

Arizona’s wastewater infrastructure is defined by its arid geography and the necessity of the “One Water” management philosophy. Unlike coastal states that discharge treated effluent into oceans, Arizona reclaims approximately 95% of its treated wastewater for agriculture, industrial cooling, turf irrigation, and underground aquifer recharge. The state’s infrastructure is overseen by the Arizona Department of Environmental Quality (ADEQ), which enforces some of the strictest Aquifer Protection Permit (APP) standards in the nation.

The sector is currently navigating a critical transition period. Rapid population growth in Maricopa and Pinal counties is driving the need for new greenfield capacity, while mature municipalities like Phoenix and Tucson are retrofitting aging bio-solids handling and secondary treatment systems. There are currently over 300 permitted wastewater treatment facilities in the state, serving a population of over 7.4 million. The regulatory environment is shifting toward Direct Potable Reuse (DPR), with ADEQ finalizing rules that will allow utilities to treat wastewater to drinking water standards without an environmental buffer.

Among US wastewater treatment plants, Arizona facilities are unusual in that effluent is treated as a water supply asset with a measurable value rather than as a waste stream with a disposal cost. Recharged effluent generates long-term storage credits that can be recovered later; Class A+ reclaimed water displaces potable demand at golf courses, parks, and power plant cooling towers; and in the Assured Water Supply framework, a utility’s reclaimed water portfolio can determine whether new development is permitted at all. That reframing changes every downstream decision, from treatment level to where the plant is sited. This page indexes every Arizona facility profiled on the site and sets out the framework that governs them.

2. Recent Developments & Projects

In the last 36 months, Arizona utilities have shifted focus from simple capacity expansion to advanced resource recovery. The Infrastructure Investment and Jobs Act (IIJA) and state-level appropriations have injected over $250 million into the Water Infrastructure Finance Authority of Arizona (WIFA) for distribution.

Notable recent trends include:

• Regionalization of Assets: Smaller municipal plants are being interconnected to larger regional facilities (like the SROG partnership) to optimize flow management and reduce per-gallon treatment costs.
• Biogas Utilization: Major facilities, including the 91st Ave WWTP, have completed massive Renewable Natural Gas (RNG) projects, turning digester gas into a revenue stream via the regional natural gas grid.
• Drought Resilience: The City of Phoenix and satellite cities are actively designing Advanced Water Purification facilities to offset reductions in Central Arizona Project (CAP) water allocations.

Two structural pressures sit underneath those trends. Colorado River shortage declarations have reduced CAP deliveries under a tiered framework, and because CAP water is the marginal supply for most Sun Corridor municipalities, every acre-foot of recoverable recharged effluent now substitutes directly for a supply the utility may not receive. Separately, the groundwater model updates that halted approvals of new Assured Water Supply certificates in parts of the Phoenix Active Management Area have made reclaimed water a development gating item, pushing homebuilders and industrial users into direct participation in wastewater capital projects.

3. Top 20 Largest Treatment Plants

The following table ranks the largest wastewater treatment plants in Arizona by design capacity. The list is dominated by the Sub-Regional Operating Group (SROG) in Phoenix and the Pima County Regional Wastewater Reclamation Department in Tucson.

Detailed Profiles: Top 5 Largest Facilities

4. Arizona Treatment Plant Directory by Region

Arizona’s treatment capacity sits in two metropolitan clusters plus a small number of border and mountain facilities. What separates them is not treatment technology, which is broadly similar across the state, but where the reclaimed water goes and what credit it earns. Phoenix-area plants feed a mix of agricultural delivery, power plant cooling, and river-corridor recharge. Tucson plants discharge to the Santa Cruz River, where effluent sustains the only perennial flow the river has. Border facilities operate under binational agreements outside the normal municipal framework. The listings below index every Arizona facility profiled on this site, grouped accordingly.

Phoenix and the SROG Partnership

The Sub-Regional Operating Group is the defining institutional arrangement in Arizona wastewater. Five cities jointly own capacity at the 91st Avenue plant while operating their own satellite facilities, which means capacity decisions at the regional plant are negotiated among partners rather than set by a single utility. For suppliers and engineers, this changes the sales and approval path: a specification at 91st Avenue can require concurrence from multiple member cities with different rate structures and capital cycles.

91st Avenue, city operations view. A second article on the Phoenix 91st Avenue Wastewater Treatment Plant covers the facility from the operating city’s perspective: the renewable natural gas project and its revenue model, the digester rehabilitation sequence, and the effluent allocation among the Palo Verde Generating Station cooling supply, the Tres Rios wetlands, and Salt River discharge.

Agua Fria Water Reclamation Facility. Our profile of the City of Phoenix Agua Fria Water Reclamation Facility covers a west-side satellite reclamation plant in the Agua Fria corridor. Satellite facilities of this type serve two purposes in the Phoenix system: they relieve trunk sewer capacity on the way to 91st Avenue, and they place reclaimed water production close to the irrigation and recharge demand that consumes it, avoiding the cost of pumping reclaimed water back upgradient.

East Valley

Mesa, Tempe, Scottsdale, Gilbert, Chandler, and Queen Creek form the fastest-growing treatment market in the state, and their plants are more likely than Phoenix’s to be built explicitly around recharge credit generation. Several East Valley utilities operate vadose zone recharge well fields adjacent to the plant, converting treated effluent directly into stored water they can recover later under an Assured Water Supply designation.

Mesa Northwest Water Reclamation Plant. The City of Mesa Northwest Water Reclamation Plant is undergoing expansion from 18 MGD toward 24 MGD to serve industrial development in the Mesa Gateway corridor alongside residential growth. Industrial load in that corridor, particularly from semiconductor and data center users, changes the influent character enough that the expansion design cannot simply scale the existing biological process.

Tempe Water Reclamation Facility. The City of Tempe Water Reclamation Facility covers the Kyrene plant, notable as a facility that was idled for years and is being restarted with membrane bioreactor treatment and rehabilitated solids handling. Restart projects of this kind are their own engineering category: the civil structures are in place, but electrical systems, instrumentation, and process equipment generally require full replacement, and the seismic and code compliance basis has moved on since original construction.

Scottsdale Water Campus. The City of Scottsdale Water Campus is the most technically advanced facility in the state and the reference installation for Arizona potable reuse. It co-locates reclamation, advanced water treatment using microfiltration, reverse osmosis, and ultraviolet advanced oxidation, and a vadose zone recharge well field on a single site. Scottsdale was the first Arizona utility to demonstrate treated wastewater purified to drinking water standards, and the campus model — treatment, purification, and recharge in one footprint — is what most subsequent Arizona advanced water purification projects are designed against.

West Valley

Surprise, Peoria, Goodyear, Avondale, and Buckeye represent the state’s greenfield market. Plants here are newer, smaller, and frequently phased, built in modular increments as subdivisions come online. Because the Assured Water Supply rules require a hundred-year demonstration before development proceeds, wastewater capacity and recharge capability in this region are often financed in partnership with developers rather than solely through utility rates.

Surprise Water Reclamation Facility. The Surprise Water Reclamation Facility serves one of the fastest-growing municipalities in Maricopa County. Facilities of this class are typically designed for Class A+ production from day one, since reclaimed water for turf, common area irrigation, and recharge is the economic justification for building ahead of demand.

Tucson and Pima County

Pima County operates a single regional system with two major plants, and its situation differs from Phoenix in one important respect: the Santa Cruz River through Tucson is effluent-dependent, so plant performance directly determines the condition of a riparian corridor that the community values and that regulators evaluate. The county’s 5-stage Bardenpho installations were driven by that relationship rather than by a conventional discharge permit calculation.

Pima County regional system. Our article on the Pima County Wastewater Reclamation Facility covers the department’s regional structure — the conveyance system feeding the two metropolitan plants, the outlying sub-regional facilities, and the Regional Optimization Master Plan that consolidated treatment and drove the Tres Rios and Agua Nueva investments.

Ina Road Water Pollution Control Facility. The Ina Road Water Pollution Control Facility article covers the plant under its former name and configuration, before the modernization that produced today’s Tres Rios facility. It remains useful as a record of the pre-upgrade treatment train and of the conditions that justified a $200 million rebuild rather than incremental improvement.

Border and International Facilities

Arizona shares a treatment obligation with Mexico that has no equivalent elsewhere in the state. Flow originating in Sonora is treated on the US side under a binational agreement, and the governing framework, funding path, and capacity drivers all sit outside normal municipal practice.

Nogales International Wastewater Treatment Plant. The International Boundary and Water Commission Nogales International Wastewater Treatment Plant treats combined flow from Nogales, Arizona and Nogales, Sonora, discharging to the Santa Cruz River. It is operated under the United States Section of the IBWC rather than by a municipality, and its central infrastructure risk is the aging International Outfall Interceptor that conveys flow to the plant. Capacity and condition here are driven by cross-border growth and by the interceptor’s structural state rather than by local service population, which puts the project on a federal funding and approval cycle rather than a municipal one.

5. Plants with Approved Budgets & Expansion Projects

A. Major Projects Under Construction (2024-2026)

B. Projects in Design/Planning Phase (2025-2028)

• Advanced Water Purification (AWP) Facility – Phoenix
  • Budget: Est. $400 – $600 Million
  • Scope: A large-scale Direct Potable Reuse (DPR) facility located at 91st Ave. Will treat effluent to drinking water standards using Ozone-BAC or RO-UV/AOP.
  • Status: Pilot testing complete; Engineering design procurement underway.
• Val Vista Water Treatment Plant Rehabilitation
  • Budget: $110 Million
  • Scope: Major electrical and mechanical upgrades to existing infrastructure shared by Mesa and Phoenix.
  • Status: Design Phase.
• Buckeye WRF Expansion Phase 3
  • Budget: $75 Million
  • Scope: Doubling capacity to meet explosive housing growth in the far West Valley.
  • Status: Planning/Pre-design.

Summary Statistics: Arizona Capital Investment

6. Regulatory & Compliance Landscape

Arizona’s regulatory framework is uniquely tailored to aquifer protection. The Arizona Pollutant Discharge Elimination System (AZPDES) governs surface discharges, but the Aquifer Protection Permit (APP) program is the primary driver for treatment standards, as most plants discharge to the ground (recharge).

• Class A+ Reclaimed Water: The gold standard in Arizona. Requires filtration and disinfection with zero detectable fecal coliforms and turbidity below 2 NTU. This allows for unrestricted reuse (parks, schools, golf courses).
• PFAS/PFOA: ADEQ is currently conducting statewide sampling. While no enforceable state MCL exists yet, major utilities (Tucson Water, Phoenix) are proactively installing treatment or shutting down impacted wells.
• Direct Potable Reuse (DPR): Arizona is finalizing a regulatory pathway for “Advanced Water Purification,” which will remove the requirement for an environmental buffer (aquifer) before reuse water enters the drinking water distribution system.
• Reclaimed Water Classes A through C: ADEQ defines a graded set of reclaimed water classes by treatment level and permitted end use, with A+ and A allowing the broadest unrestricted applications and lower classes restricted to limited-access irrigation and similar uses. Specifying the class the project must achieve is the first design decision, because it determines whether filtration and continuous turbidity monitoring are required.
• Recharge and recovery permitting: Underground storage facility permits, water storage permits, and recovery well permits are issued by the Arizona Department of Water Resources, separately from ADEQ’s treatment permits. A recharge project therefore carries two parallel approval tracks under two agencies.

Long-term storage credits and the Assured Water Supply rule

The mechanism that makes Arizona wastewater economics distinctive is the long-term storage credit. Effluent recharged at a permitted underground storage facility accrues credits, subject to a cut to the aquifer, that the utility can recover later or use to demonstrate a hundred-year assured supply for new development. That turns a treatment plant into a supply asset with a balance sheet value, and it explains why Arizona utilities routinely build to Class A+ when a lower class would satisfy the discharge requirement. The credit accounting is administered by ADWR and does not appear anywhere in the ADEQ permit, so a project evaluation based only on treatment permitting will miss the actual business case.

7. Infrastructure Challenges & Opportunities

The Salt Balance Problem: As water is reused multiple times in a closed loop (One Water), Total Dissolved Solids (TDS) increase (salinity). Inland utilities cannot easily discharge brine. This presents a massive opportunity for vendors specializing in Brine Minimization and Zero Liquid Discharge (ZLD) technologies.

Growth vs. Water Supply: The Assured Water Supply rules require developers to prove 100 years of water. In areas where groundwater is restricted (Pinal County), developers are partnering with utilities to fund advanced wastewater treatment to create “recharge credits,” essentially manufacturing their own water supply to allow construction to proceed.

Industrial load from advanced manufacturing: Semiconductor fabrication and data center development across the Phoenix and Mesa corridors introduces high-purity process water demand, ultrapure water reject streams, and industrial discharges with characteristics unlike municipal influent. Utilities serving these corridors are negotiating pretreatment agreements and, in some cases, dedicated industrial reclamation capacity, which is a distinct market from conventional municipal expansion.

8. Technology Trends in Arizona

• Vadose Zone Recharge Wells: Unlike traditional injection wells, these use gravity to recharge aquifers in the unsaturated zone. Widely used due to lower O&M costs.
• Ozone-Biofiltration (Ozone-BAC): Gaining traction over Reverse Osmosis for reuse projects because it destroys contaminants without creating a brine stream that is difficult to dispose of in a landlocked state.
• Advanced Metering Infrastructure (AMI) & AI: Used extensively to detect leaks and optimize distribution networks.
• 5-stage Bardenpho and advanced nutrient removal: The configuration of choice where effluent sustains a riparian corridor, as on the Santa Cruz River through Tucson, and increasingly where recharge permits impose nitrogen limits tied to drinking water criteria.
• Membrane bioreactors for satellite and restart projects: Favored where footprint is constrained or where an existing basin structure can be repurposed, as in the Kyrene rehabilitation.
• Digester gas to renewable natural gas: Proven at scale at 91st Avenue, and now evaluated at mid-size facilities wherever a pipeline interconnection is within reach.

9. Comparing Arizona Facility Classes

Arizona facilities sort by what happens to the effluent rather than by treatment technology, which is broadly similar statewide. The table below summarizes how those classes differ in the terms that drive design and capital planning.

10. Benchmarking and Site Selection

A state directory gets used to size a market, to find a comparable facility for a design or bid basis, and to anticipate permit requirements. In Arizona all three start from what the effluent is for.

Selecting a comparable facility

Match on effluent destination and reclaimed water class before matching on flow. A 20 MGD plant producing Class A+ for a recharge well field and a 20 MGD plant discharging secondary effluent to a wash have different filtration, disinfection, monitoring, and instrumentation scopes, and the cost gap is larger than any difference attributable to capacity. Then check whether the facility is part of a joint ownership arrangement, because SROG-style shared capacity changes governance, approval timelines, and how cost is allocated.

Worked example: sizing a comparison set

Suppose a West Valley municipality needs a benchmark for a new 10 MGD Class A+ plant with an adjacent vadose zone recharge well field. Filtering the directory by effluent destination eliminates 91st Avenue and the Tucson river dischargers immediately. What remains is the growth-driven satellite group: Surprise, and the Mesa and Tempe facilities if the recharge component dominates. Before normalizing to a per-MGD basis, separate the recharge well field cost from the treatment plant cost, since well field capital varies with depth to groundwater and soil profile far more than with plant capacity, and a comparison that bundles them will produce a per-MGD figure that transfers to no other site. Scottsdale is instructive as a design reference but not as a cost comparable, since the advanced purification train there serves a different purpose. Two or three adjusted comparables will beat a dozen matched on flow.

Comparing Arizona to other state markets

Arizona’s credit-driven economics are unusual, and neighboring state directories help separate what is a Colorado River basin constraint from what is specific to Arizona water law. The Nevada wastewater treatment plants directory covers the closest analog, where treated effluent returned to Lake Mead earns return-flow credits against the state’s Colorado River allocation — a different accounting mechanism serving the same purpose as Arizona’s storage credits. The California wastewater treatment plants directory covers the largest reuse market in the country, where coastal disposal remains available and brine management is the limiting factor rather than salt accumulation in a closed inland loop. The Texas wastewater treatment plants directory covers the state with the longest operating record in direct potable reuse, useful precedent as ADEQ finalizes its advanced water purification pathway.

11. Field Notes

The permit that matters may not be the treatment permit

An Arizona reuse project typically requires an Aquifer Protection Permit from ADEQ and, separately, underground storage facility and water storage permits from ADWR. The two agencies evaluate different questions on different timelines, and a schedule built around ADEQ review alone will slip. On projects where storage credits are the financial justification, the ADWR track is the one that determines whether the project delivers its intended value.

Salt accumulates in a closed loop

Every cycle of use adds total dissolved solids, and a landlocked utility has no easy outlet for the concentrate that removing them produces. This is why ozone and biological activated carbon are frequently preferred over reverse osmosis for Arizona purification trains despite RO’s superior contaminant rejection: the treatment decision is being made on brine disposal, not on treatment performance. Any advanced treatment proposal for an Arizona site should lead with what happens to the residual stream.

12. Permitting & Design Standards Reference

Arizona splits authority between two state agencies, and a reuse or recharge project touches both.

Treatment and discharge permitting in Arizona is administered by the Arizona Department of Environmental Quality under the Aquifer Protection Permit program and the Arizona Pollutant Discharge Elimination System, with reclaimed water quality classes and permitted end uses defined in Arizona Administrative Code Title 18. Underground storage facility permits, water storage permits, recovery well permits, and long-term storage credit accounting are administered separately by the Arizona Department of Water Resources.

Specification checklist for an Arizona project

1. Establish the effluent destination and the reclaimed water class the project must achieve before selecting any unit process.
2. Confirm whether an Aquifer Protection Permit, an AZPDES permit, or both apply.
3. Determine whether long-term storage credits are part of the project justification, and identify the ADWR permits required to earn them.
4. Verify the Active Management Area and any Assured Water Supply constraints affecting the service area.
5. Establish the salt balance across the intended reuse cycles and identify the concentrate management pathway before specifying any membrane process.
6. Confirm nitrogen limits, which for recharge projects are frequently set against drinking water criteria rather than surface water objectives.
7. For recharge components, obtain depth to groundwater, vadose zone soil profile, and percolation data early, since these govern well field cost more than plant capacity does.
8. Identify any joint ownership or sub-regional operating arrangement and the concurrence required from partner cities.
9. Characterize industrial contribution, particularly semiconductor, data center, and mining-adjacent loads, and confirm pretreatment requirements.
10. Establish peak flow and diurnal variation, noting that arid-climate systems generally have low inflow and infiltration but pronounced seasonal irrigation demand on the reuse side.
11. Confirm biosolids end use and applicable land application or landfill constraints.
12. Verify operator certification grade requirements under ADEQ rules for the facility class.
13. Confirm WIFA participation and the procurement and reporting conditions attached to SRF financing.
14. Identify applicable AWWA, WEF, and ANSI/ASME standards for the specific equipment package.

13. Resources for Engineers & Operators

• AZ Water Association: The state chapter of AWWA/WEF. Hosts the annual conference in Phoenix (Spring). Link to Association
• WIFA (Water Infrastructure Finance Authority): The primary issuer of SRF loans and water supply development grants. Link to WIFA
• ADEQ Operator Certification: Manages testing and licensure for Grades 1-4 wastewater operators. Link to Certification
• Arizona Department of Water Resources: Administers Active Management Areas, Assured Water Supply designations, recharge permits, and long-term storage credit accounting.
• Central Arizona Project: Operates the canal system delivering Colorado River water and participates in underground storage and recovery programs.
• WateReuse Arizona: Section focused on reclaimed water policy and advanced water purification development.
• ADEQ eLicense and permit search: Public access to APP and AZPDES permits, compliance records, and inspection history.

14. FAQ Section

How many wastewater treatment plants are in Arizona?

There are over 300 permitted wastewater treatment facilities in Arizona, ranging from massive regional plants like the 204 MGD 91st Ave plant to small package plants serving remote communities and RV parks.

What is the largest wastewater plant in Arizona?

The 91st Ave Wastewater Treatment Plant is the largest, with a capacity of 204.5 MGD. It is owned by the Sub-Regional Operating Group (SROG), which includes Phoenix, Glendale, Mesa, Scottsdale, and Tempe.

What are the primary drivers for WWTP projects in Arizona?

Unlike the East Coast (CSO/SSO compliance), Arizona projects are driven by 1) Capacity expansion for rapid housing growth, and 2) Advanced treatment for water reuse (aquifer recharge) to generate long-term water storage credits.

Is Arizona implementing Direct Potable Reuse (DPR)?

Yes. Arizona is in the advanced stages of finalizing regulations for DPR (termed Advanced Water Purification). The City of Phoenix and Scottsdale are actively planning facilities that will treat effluent to drinking water standards for direct introduction into the potable supply.

What is Class A+ reclaimed water and when is it required?

Class A+ is Arizona’s highest reclaimed water classification, requiring filtration, disinfection to non-detectable fecal coliform, turbidity below 2 NTU, and nitrogen treatment. It permits the widest range of end uses, including irrigation of parks, schoolyards, and golf courses, and it is the practical prerequisite for recharge projects intended to generate storage credits. Many Arizona utilities build to Class A+ even where a lower class would satisfy their permit, because the classification determines what the water is worth rather than merely whether it complies.

What is a long-term storage credit and why does it matter to a treatment plant?

When a utility recharges treated effluent at a permitted underground storage facility, it accrues long-term storage credits with the Arizona Department of Water Resources, subject to a cut left in the aquifer. Those credits can be recovered later or used to demonstrate an assured water supply for new development. The effect is that treatment capacity converts into supply, which is why Arizona utilities evaluate plant upgrades against water portfolio value rather than against compliance cost alone. The accounting sits entirely outside the ADEQ treatment permit.

Why is brine disposal such a constraint in Arizona?

Reverse osmosis and similar processes produce a concentrated residual stream, and a landlocked state has no ocean outfall to receive it. Deep well injection is limited by geology and permitting, evaporation ponds consume land and create their own closure liability, and discharging concentrate to a wash is generally not permissible. Every cycle of reuse also raises total dissolved solids in the system, compounding the problem. This is the main reason ozone with biological activated carbon is frequently selected over reverse osmosis for Arizona purification projects despite RO’s stronger contaminant rejection.

How does Arizona’s approach differ from California’s?

Both states are reuse leaders, but their constraints run opposite. California has coastal disposal available for both effluent and brine, so its limitation is treatment cost and permitting rather than residual management, and its reuse framework is built around environmental buffers and recharge basins. Arizona has no disposal outlet, which makes salt balance and concentrate handling the binding constraint, and its framework is built around aquifer storage credits administered as a water right rather than as an environmental compliance measure.

15. Conclusion

Arizona has spent three decades building the institutional machinery to treat wastewater as water supply, and Colorado River shortage has now made that machinery load-bearing. Storage credits, Class A+ reclaimed water, and the Assured Water Supply framework mean a treatment plant here is evaluated on what it adds to a utility’s water portfolio, not on what it costs to comply. The next phase, advanced water purification for direct potable reuse, is a continuation of the same logic rather than a departure from it, and the constraint on how fast it arrives is concentrate management rather than treatment capability.

Use this directory as an index organized around that framework. Start from the effluent destination and the reclaimed water class, confirm which agency holds the permit that governs the project’s value, and only then compare capacity and cost. The regional listings above link to detailed profiles of every Arizona facility covered on this site, and the cross-state comparisons in Section 10 help separate a Colorado River basin constraint from a feature of Arizona water law.