Maricopa County Water Quality by City: HAA5, TTHM, and PFAS Compared

Across Maricopa County, tap water quality varies by city based on source water blend, disinfection method, and proximity to industrial or military contamination. For PFAS, Tempe recorded PFOS at 55.80 ng/L and PFOA at 38.70 ng/L during EPA UCMR 5 monitoring in January 2025, more than thirteen times the 4 ppt federal limit, per data at waterutilityreport.com. Gilbert recorded PFOS at 9.80 ng/L and PFOA at 6.50 ng/L. Peoria had PFOA at 5.60 ng/L. Phoenix Water Services draws almost entirely from the Salt and Verde rivers, giving it a lower PFAS exposure profile than groundwater-reliant systems. For HAA5 and TTHM, most Maricopa County utilities use chloramine as their secondary disinfectant. Chloramine produces lower TTHM than free chlorine, but HAA5 levels can remain comparable. Federal MCLs are 80 ppb for TTHM and 60 ppb for HAA5. Each city's annual Consumer Confidence Report at epa.gov/ccr documents actual detected levels. Reverse osmosis reduces PFAS. Catalytic carbon addresses chloramine byproducts. Call (928) 451-1591 to schedule a free in-home water test.

How Maricopa County cities get their tap water

Maricopa County's eight major cities draw water from three main sources: Colorado River water delivered via the Central Arizona Project (CAP), Salt River and Verde River water managed by the Salt River Project (SRP), and groundwater extracted from basin aquifers beneath the valley. Most utilities blend two or more of these sources in proportions that shift seasonally based on availability and pricing. The blend matters because each source carries a distinct chemical profile. CAP water is relatively soft but subject to seasonal variation in algae-related compounds. SRP surface water from the Salt and Verde rivers is treated extensively before distribution. Groundwater in parts of the West and East Valley has accumulated PFAS from industrial and military sources over decades.

Disinfection chemistry is the other primary variable. Almost every Maricopa County utility uses chloramination as its secondary disinfection step, adding ammonia to react with residual free chlorine and form monochloramine before water enters the distribution network. Chloramine is more stable than free chlorine across the long pipe runs of a sprawling desert city, which is why the valley adopted it. That stability comes at a cost: chloramine does not fully decompose at the tap, is associated with specific disinfection byproduct formation, and requires catalytic carbon rather than standard activated carbon for residential removal.

Phoenix Water Services operates five treatment plants that together handle the full blend before distribution to more than 1.6 million residents, according to phoenix.gov/waterservices. Scottsdale operates its own surface water treatment plants on CAP and SRP supply with limited groundwater supplementation. Mesa, Chandler, Tempe, Gilbert, Peoria, and Surprise each operate separate utilities with different source blends and infrastructure. Each utility reports its annual water quality data in a Consumer Confidence Report mailed to customers and posted at epa.gov/ccr.

PFAS in Maricopa County: which cities exceeded the federal limit

The EPA fifth Unregulated Contaminant Monitoring Rule required all public water systems serving more than 3,300 people to test for 29 PFAS compounds from January 2023 through December 2025. Results are publicly accessible through the EPA UCMR 5 Data Finder at epa.gov/dwucmr/fifth-unregulated-contaminant-monitoring-rule-data-finder, where homeowners can search by state or water system name. The EPA finalized Maximum Contaminant Levels for PFAS in April 2024: PFOA at 4 ppt, PFOS at 4 ppt, HFPO-DA (GenX chemicals) at 10 ppt, PFNA at 10 ppt, and PFHxS at 10 ppt, with a compliance deadline of April 2029. Nationally, more than 3,500 community water systems had detectable PFAS, representing approximately 95 percent of monitored systems, according to Environmental Working Group analysis at ewg.org/interactive-maps/pfas_contamination.

Within Maricopa County, Tempe recorded the highest PFAS concentrations during UCMR 5 monitoring. Tempe detected PFOS at 55.80 ng/L and PFOA at 38.70 ng/L in January 2025 samples, per data compiled at waterutilityreport.com. Both readings exceed the 4 ppt federal limit by more than thirteen times for PFOS and nearly ten times for PFOA. Tempe draws water from a blend of CAP supply and groundwater wells. Groundwater in portions of the East Valley, including areas near Falcon Field Airport and industrial corridors in the Tempe and Chandler area, has documented PFAS from historic use of aqueous film-forming foam. The ADEQ monitors PFAS statewide and documents Arizona contamination sites at azdeq.gov.

Gilbert, which blends SRP surface water with groundwater wells, recorded PFOS at 9.80 ng/L and PFOA at 6.50 ng/L during UCMR 5 monitoring, according to waterutilityreport.com. Peoria had PFOA detections at 5.60 ng/L. All three municipalities exceed the 4 ppt MCL that takes effect for utility compliance in 2029, meaning their tap water may legally contain PFAS above the new limit until that deadline. Phoenix, which draws 97 to 99 percent of its supply from Salt River and Verde River surface water, shows a different risk profile from groundwater-reliant systems. Scottsdale, Mesa, Chandler, and Surprise each report their UCMR 5 results through the EPA Data Finder; homeowners in those cities should filter by their specific water system name to obtain current detection data.

For households in cities with documented PFAS above the MCL, the treatment gap between now and 2029 is the practical reason to install point-of-use reverse osmosis today. Utilities have until April 2029 to achieve compliance, and during that window tap water at affected systems may continue to arrive above the new limit without violating the current regulatory threshold. A certified RO system addresses that gap at the kitchen tap without waiting for utility-level capital improvements.

HAA5 and TTHM: disinfection byproducts across Maricopa County

HAA5, the sum of five regulated haloacetic acid compounds, and TTHM, the sum of four trihalomethane species, form when disinfectants react with natural organic matter dissolved in source water. The reaction is unavoidable wherever water is chemically disinfected, because organic carbon from decaying plant material is present in every surface water source. The EPA regulates TTHM at 80 micrograms per liter and HAA5 at 60 micrograms per liter, both measured as running annual averages. Long-term consumption of water above those MCLs is associated with elevated risk of bladder cancer and adverse reproductive outcomes, according to EPA health summaries at epa.gov.

The disinfection chemistry of a utility's distribution system determines which DBPs dominate its profile. Free chlorine, used in initial treatment, reacts with organic matter to produce high concentrations of TTHM including chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Chloramine, the secondary disinfectant used throughout Maricopa County, produces significantly lower TTHM than free chlorine under comparable source water conditions. However, chloramine reacts with organic nitrogen precursors to produce other byproducts including haloacetonitriles and iodoacids. HAA5 formation under chloramination can be comparable to free chlorine systems depending on source water organic content and contact time.

Because Maricopa County utilities universally use chloramination in their distribution networks, the valley's tap water is characterized by lower TTHM values than free chlorine systems of comparable scale. Each utility's CCR documents the running annual average for TTHM and HAA5 measured at monitoring locations throughout its distribution network. Phoenix posts its CCR at phoenix.gov/waterservices. Scottsdale, Mesa, Chandler, Tempe, Gilbert, Peoria, and Surprise each post their annual CCR at their utility websites, and all are accessible at epa.gov/ccr. Homeowners who want to understand their actual exposure should request the most recent CCR or use the EPA CCR portal to pull historical values by monitoring location.

At the household level, the most practical treatment for DBP reduction at every fixture is a whole-home catalytic carbon filter installed on the main supply line. Catalytic carbon is specifically formulated to remove chloramine and the DBPs it forms, where standard granular activated carbon has insufficient reactivity for chloramine at residential flow rates. Sizing matters: four to six minutes of empty bed contact time is typically required for effective chloramine removal at Arizona usage rates. A whole-home filter addresses every shower, kitchen faucet, and appliance simultaneously. A point-of-use RO system at the kitchen tap adds PFAS and TDS reduction at the drinking water source.

Phoenix tap water: surface water advantage and remaining concerns

Phoenix Water Services delivers water to more than 1.6 million residents using five treatment plants that process water from the Salt River and Verde River, with Colorado River supplementation through CAP during high-demand periods, according to the City of Phoenix at phoenix.gov/waterservices. That surface water origin gives Phoenix a structural advantage on PFAS: rivers and reservoirs dilute contamination more broadly than confined aquifer systems beneath contaminated soil. Phoenix PFAS results from UCMR 5 are accessible through the EPA Data Finder at epa.gov/dwucmr, filtered to the City of Phoenix water system. Residents who want Phoenix-specific detection results should review the CCR directly at phoenix.gov/waterservices rather than relying on county-level summaries that may reflect groundwater systems.

The concerns that remain for Phoenix tap water are hardness and disinfection byproducts. Phoenix water runs 12 to 22 grains per gallon of hardness, among the highest in the United States. At those levels, calcium and magnesium scale deposits form inside water heaters, dishwashers, and plumbing fittings within months. Ion-exchange water softeners are the standard residential solution; no other technology provides comparable scale protection at Arizona hardness levels. Chloramine disinfection adds the DBP profile described above, requiring catalytic carbon filtration. For households that also want PFAS protection at the drinking tap, an NSF 58-certified RO unit completes the treatment stack.

Scottsdale, Mesa, and Chandler tap water quality

Scottsdale Water operates two advanced water treatment plants that process SRP and CAP supply, making Scottsdale predominantly a surface water city with limited groundwater contribution under normal operating conditions. Scottsdale's treatment processes include microfiltration, ozonation, and granular activated carbon before chloramination, producing tap water with a relatively low organic precursor load entering the distribution system. Scottsdale posts its annual Water Quality Report at scottsdaleaz.gov. Mesa Utilities draws from SRP and CAP surface water with some groundwater blending in portions of its service area, particularly on the east side where Mesa's water system borders Gilbert's groundwater-reliant zones. Mesa posts its CCR at mesaaz.gov.

Chandler Utilities uses a blend of CAP surface water, SRP water, and reclaimed groundwater in different portions of its service territory. Chandler's CCR is available at chandleraz.gov. For all three cities, TTHM and HAA5 values appear in the annual CCR's contaminants table alongside the MCL and any five-year average. The UCMR 5 dataset, accessible at the EPA Data Finder filtered to each system name, shows PFAS detection data by monitoring location. Homeowners in Scottsdale, Mesa, or Chandler who are uncertain about their address's supply source can call their utility's customer service line to identify which water plant serves their zone.

Gilbert, Tempe, Peoria, and Surprise tap water quality

Gilbert Water operates a system that blends SRP surface water with groundwater from the San Tan area. The groundwater portion of Gilbert's supply reflects PFAS accumulation documented in portions of the East Valley, which appears in Gilbert's UCMR 5 results: PFOS at 9.80 ng/L and PFOA at 6.50 ng/L, per data at waterutilityreport.com. Gilbert posts its annual Water Quality Report at gilbertaz.gov. Tempe Water's January 2025 UCMR 5 sample showed PFOS at 55.80 ng/L and PFOA at 38.70 ng/L, the highest PFAS concentrations documented for a Maricopa County municipal utility during the monitoring period. Tempe uses a mix of CAP and groundwater supply. The ADEQ documents PFAS site investigations in Maricopa County at azdeq.gov, including near-airport and near-military zones where aqueous film-forming foam was historically used.

Peoria, which draws from a combination of CAP surface water and groundwater in the Agua Fria and New River subbasins, had PFOA detected at 5.60 ng/L during UCMR 5 monitoring. Peoria posts its Consumer Confidence Report at peoriaaz.gov. Surprise Utilities serves a growing west-side service area and draws primarily from groundwater in the West Valley, supplemented by CAP water deliveries. Surprise's UCMR 5 results are accessible through the EPA Data Finder at epa.gov/dwucmr by searching for Surprise or the Arizona water system identifier. For households in Gilbert, Tempe, or Peoria, all of which have documented PFAS above the 4 ppt federal MCL, the practical treatment path is a point-of-use RO system at the kitchen tap. Contact Aqua Wellness at (928) 451-1591 to schedule a free in-home water test.

What treatment each contaminant requires in a Maricopa County home

The right treatment combination depends on which contaminants your city's supply carries. No single system addresses the full Maricopa County tap water profile. The standard treatment stack for the Phoenix metro area addresses hardness, chloramine, disinfection byproducts, and PFAS as separate problems requiring separate technologies. For households in Tempe, Gilbert, or Peoria, PFAS should be treated as an immediate priority. For households in Phoenix or Scottsdale, the PFAS urgency is lower but hardness and DBP treatment remain essential.

• NSF/ANSI 58 certified reverse osmosis at the kitchen tap: greatly reduces PFOA, PFOS, and other PFAS; also removes arsenic, nitrates, TDS, fluoride, and lead; the EPA-recommended technology for residential PFAS reduction per epa.gov/water-research/identifying-drinking-water-filters-certified-reduce-pfas
• Whole-home catalytic carbon filtration on the main supply line: removes chloramine and HAA5/TTHM disinfection byproducts at every fixture including showers, faucets, and appliances; must be catalytic carbon rather than standard GAC to break the chloramine bond at residential contact times
• Ion-exchange water softener downstream of the carbon filter: exchanges calcium and magnesium for sodium to eliminate scale formation at Phoenix-area hardness levels of 12 to 22 GPG; has no effect on PFAS, chloramine, or DBPs
• Standard activated carbon pitcher filters: insufficient for chloramine or PFAS removal; may reduce chlorine taste but do not address the Maricopa County contaminant profile
• Water softeners alone: address hardness only; leave PFAS, chloramine, and disinfection byproducts untouched
• UV systems: effective against biological contaminants; have no effect on PFAS, HAA5, TTHM, or hardness; appropriate as a supplemental layer for private well owners

A complete Phoenix-area treatment stack installs a whole-home catalytic carbon filter on the main supply line to handle chloramine and DBPs at every fixture, a water softener downstream to exchange calcium and magnesium before water reaches appliances, and an NSF 58-certified RO system under the kitchen sink for PFAS, arsenic, and TDS reduction at the drinking tap. Contact Aqua Wellness at (928) 451-1591 to schedule a free in-home water test. An in-home test measures actual levels at your tap rather than relying on system-wide averages from the annual CCR.

How to find and read your city's Consumer Confidence Report

Every public water system in the United States serving more than 25 people must publish an annual Consumer Confidence Report documenting the contaminants detected in its water during the prior calendar year, the MCL for each regulated substance, and source water information. Utilities must distribute the CCR to customers each year by July 1. The EPA maintains a national CCR portal at epa.gov/ccr where homeowners can search for their utility by state, county, or system name and download current and historical reports.

When reading a CCR, locate the contaminants table. For TTHM, look for the highest running annual average or locational running annual average column. The MCL is 80 ppb; any value above that indicates a violation. For HAA5, the MCL is 60 ppb. For PFAS, the CCR may show UCMR 5 results separately or reference the EPA data finder. Homeowners can supplement the CCR with the EPA UCMR 5 Data Finder at epa.gov/dwucmr by searching for their specific water system name. Aqua Wellness also offers free in-home water testing at your tap for Phoenix, Scottsdale, Tempe, Mesa, Chandler, Gilbert, and Peoria addresses. Call (928) 451-1591 to schedule.