Arizona Private Well Water Quality 2026

Arsenic: Arizona’s Most Widespread Well Water Threat

Arizona has three distinct geological sources of naturally occurring arsenic. The state’s Basin and Range province contains volcanic rock formations — the Superstition Mountains, Mingus Mountain, San Francisco volcanic field and dozens more — all of which contain arsenic-bearing minerals. Precambrian granitic basement rock adds a second source, and basin-fill sedimentary deposits adsorb arsenic from the surrounding geology and release it directly into groundwater. The result is arsenic exposure across the entire state, not just isolated hotspots.

The scale of Arizona’s arsenic problem is documented in a peer-reviewed study published in the Journal of Contemporary Water Research & Education: approximately 20.7% of sampled wells in Arizona exceed the EPA’s maximum contaminant level of 10 ppb — nearly double the national average of 12%. The central and southern regions of the state show the highest concentration of exceedances, though elevated arsenic has been documented statewide. The Arizona Department of Health Services (ADHS) states plainly: arsenic is present in almost all of Arizona’s groundwater supplies.

The Phoenix metropolitan area is a particular concern. DrillerDB’s 2025 Arizona well guide, drawing on ADHS and USGS data, reports that over half of sampled wells in the Phoenix area exceed 5 µg/L of arsenic — a level at which health organisations recommend treatment. In the Tucson and Sierra Vista areas, more than 10% of wells exceed this threshold. Arsenic is colourless, odourless, and tasteless. It cannot be detected without a laboratory test, and long-term exposure is linked to cancers of the bladder, lung, and skin, as well as cardiovascular disease and developmental effects in children.

Mining history compounds the problem. Arizona’s extensive gold and copper mining operations disturb iron-sulfur bearing rocks, accelerating the release of arsenic into surrounding groundwater. Communities near legacy mine sites — scattered across central and northern Arizona — face both naturally elevated arsenic and the potential for mining-related legacy contamination in their wells.

PFAS Contamination from Military Bases and Airports

Arizona is home to several major military installations and airports that used PFAS-containing aqueous film-forming foam (AFFF) for decades. This foam was standard equipment for training exercises and aircraft fire suppression. The PFAS soaked into the soil and migrated into the underlying aquifers, contaminating groundwater used by both public water systems and private wells.

The two primary PFAS contamination zones in Arizona are:

• Tucson International Airport Area (TIAA) — an EPA-designated Superfund site spanning ten square miles in southeastern Tucson. The Arizona Air National Guard base at this site used AFFF for decades. ADEQ confirmed that three private drinking water wells in the south-side area were impacted with PFAS above EPA health advisory levels. Separately, state testing reported by Tucson Water Director Tim Thomure found one private well at 2,300 parts per trillion (ppt) — more than 570 times the current 4 ppt EPA limit. ADEQ and the Air National Guard are working to ensure affected wells are no longer used for drinking water, and ADEQ is providing bottled water to residents with no alternative supply.
• Luke Air Force Base (West Valley, Maricopa County) — in February 2021, Luke AFB notified the nearby Valley Utilities Water Company that its supply wells had PFAS levels above the EPA Health Advisory Level of 70 ppt. ADEQ subsequently wrote to ten public water systems within a four-mile radius of Luke, serving more than 50,000 people, to assess potential PFAS impacts. The Luke AFB area remains an active remediation and monitoring zone.

ADEQ has tested 693 public water systems statewide as part of a proactive PFAS screening programme, with 12% of those systems detecting PFAS above at least one MCL in the completed Phase 1 results (December 2024). However, ADEQ explicitly does not regulate private well water quality. Private well owners near any military base, airport, firefighting training facility, or industrial site must arrange their own testing — no state body will do this for them.

Arizona has no state-level PFAS MCLs of its own and cannot adopt standards stricter than federal limits under current state law. The federal MCL of 4 ppt for PFOA and PFOS has been enforceable since April 2024, applying to public water systems. The original compliance deadline was April 2029; in May 2025 the EPA announced its intent to extend this to 2031, with a proposed rule issued in November 2025 and finalisation expected spring 2026. Private wells are not covered by this rule regardless of the compliance date.

Chromium-6: The Third Contaminant in Arizona Groundwater

Chromium-6 (hexavalent chromium) is a known human carcinogen that occurs naturally in Arizona groundwater through the weathering of chromium-bearing rocks — the same geological processes that drive arsenic contamination. It is also produced by industrial activity. Because Arizona’s groundwater systems are heavily used for drinking water across the Phoenix metropolitan area, chromium-6 is a real concern for private well owners whose water comes entirely from these aquifers.

There is currently no federal MCL specific to chromium-6. The federal standard covers total chromium at 100 ppb, but health advocates argue this standard is inadequate given chromium-6’s carcinogenic properties. At the Tucson International Airport Area Superfund site, a 2016 USGS study of 46 groundwater wells found detectable chromium in every single well, with more than 75% of the total chromium present in the more toxic hexavalent form. For private well owners who draw from the same aquifer as these monitoring wells, the implication is clear: chromium-6 testing is not optional.

University researchers at Arizona State have documented that groundwater in parts of the Phoenix metro area carries elevated chromium-6 levels, particularly in areas served primarily by wells rather than surface water. Well owners in Maricopa County communities relying heavily on groundwater — including parts of Mesa, Chandler, and Scottsdale — should include chromium-6 in their testing panel. Critically, arsenic treatment systems installed by many Arizona utilities are designed to remove arsenic only; they do not remove hexavalent chromium. Reverse osmosis is the most reliable point-of-use technology for both contaminants.

Nitrate, Bacteria, and Additional Risks

In Arizona’s agricultural valleys — the Salt River Valley, Yuma area, and parts of Pinal County — nitrate contamination from fertiliser and irrigation runoff is a documented risk in shallow wells. High nitrate concentrations are particularly dangerous for infants under six months old. ADHS recommends nitrate testing for all new wells, and annually where infant formula preparation is involved.

Coliform bacteria can contaminate private wells where wellheads are insufficiently sealed, where flooding occurs — a risk in Arizona’s monsoon season — or where septic systems are sited too close to well casings. Arizona counties vary in their septic setback requirements, and older rural properties may have inadequate separation distances. Bacterial testing is recommended annually for all private wells, and immediately after any flooding event.

Regulatory Situation for Arizona Well Owners

Private wells in Arizona are governed by the Arizona Department of Water Resources (ADWR) for permitting and construction standards, but ADEQ explicitly does not regulate the water quality of private wells. There is no mandatory testing requirement for well owners, no state notification system if contamination is found nearby, and no enforcement mechanism requiring treatment even if contaminants exceed federal limits in a private well.

Most private domestic wells in Arizona are classified as “exempt wells” — pumping 35 GPM or less for household purposes. This exemption from metering and reporting rules means the state has limited data on what Arizona’s private well population is actually drinking. The burden of testing, interpretation, and remediation falls entirely on individual well owners.

Check our Arizona municipal water quality page for city-by-city tap water data, or use our live boil water notice tracker for active advisories across the state.

Known High-Risk Areas in Arizona

If you live near any of the following locations, well water testing is urgent — not precautionary.

How to Test Your Arizona Well Water — and What to Do Next

Arizona’s contamination profile — arsenic from geology, PFAS from military and aviation, chromium-6 from both — means every private well owner in the state should test their water regardless of location. ADHS recommends testing all new wells for arsenic and other primary metals as a baseline, with ongoing annual testing for bacteria and nitrate. For any property near a military installation, airport, or legacy industrial site, a full PFAS panel should be treated as urgent.

Use ADEQ’s interactive PFAS map at azdeq.gov to check whether public water system detections have been recorded near your property — this can indicate groundwater contamination in your area even if your private well has not been tested. Contact your county health department to locate a state-certified laboratory for private well testing.

For filter options, our well water filter guide covers reverse osmosis systems — the most effective option for arsenic, PFAS, and chromium-6 simultaneously — plus UV disinfection for bacteria and whole-house systems for comprehensive well protection. You can also browse our full water filter solutions page or check your ZIP code for local water quality context.

For city-specific municipal water data, see our pages on Phoenix, Tucson, Scottsdale, Chandler, Gilbert, Mesa, and Glendale. For other Southwest well water data, see our Ohio wells page and the full private well water directory.