Arizona Tap Water Quality (2026): Grades, Arsenic and EPA Records

Arizona’s large water systems grade below average on TapWaterSafety. The 21 Arizona systems we grade average 60.7 out of 100, a D, which ranks 27th of 29 states with at least 10 systems. None earns an A, and only one earns a B. Arsenic above health guidelines is a top concern for all 21. That reflects arsenic that occurs naturally in much of the Southwest, at levels that are usually legal but far above stricter health-based goals. On the compliance side, 19 of the 21 had an EPA violation in the last three years, but almost all were for missed or late monitoring.

Where this data comes from

TapWaterSafety.org grades 1,000 US public water systems, each serving more than 50,000 people. Twenty-one are in Arizona, serving about 5.2 million people combined. Smaller systems and private wells are not included.

Grades run from A (85 to 100) to F (54 or below). The score weighs detected contaminants against EWG health guidelines, which are usually much stricter than legal limits, along with EPA violations, high-risk contaminants such as arsenic, PFAS and chromium-6, and source water. Our methodology page has the full formula. EPA records are from EPA ECHO compliance records, checked October 7, 2026; last 12 quarters.

Where Arizona’s water comes from

Arizona draws on four main supplies. Based on 2020 figures from the Arizona Department of Water Resources (ADWR), about 41% of the state’s water is groundwater, 36% comes from the Colorado River, 18% from in-state rivers such as the Salt and Verde, and 5% is reclaimed water.

Colorado River water reaches central and southern Arizona through the Central Arizona Project (CAP), a 336-mile system running from Lake Havasu to Tucson. CAP serves Maricopa, Pinal and Pima counties, where more than 80% of Arizonans live.

How that plays out depends on the city:

• Phoenix gets nearly 60% of its water from the Salt and Verde rivers through the Salt River Project, about 40% from the Colorado River through CAP, and about 2% from groundwater, according to the city.
• Tucson says about 90% of its drinking water is a blend of groundwater and Colorado River water. The city recharges its CAP water into aquifers and pumps it back out through wells. Its system is listed as groundwater in our data.

In our data, 12 Arizona systems are listed as surface water (one of them purchased) and 9 as groundwater. The groundwater systems actually average higher (63.6) than the surface water systems (58.5).

All 21 Arizona systems

Sorted by score. “Top concerns” are the first items each utility page lists. Click a system for full contaminant details and its EPA report link.

Why arsenic shows up everywhere

Arsenic is a top concern for every Arizona system we grade. That does not mean these systems exceed the legal limit. None of the 21 has an arsenic MCL violation in its EPA record. The concern flag means detected levels are well above a health guideline that is much stricter than the law.

The gap between those two numbers is large:

• EPA’s legal limit (maximum contaminant level) for arsenic is 10 parts per billion (ppb). EPA adopted it in 2001, and water systems had to comply by January 23, 2006.
• California’s public health goal for arsenic is 0.004 ppb, set by the state’s Office of Environmental Health Hazard Assessment in 2004. It is based on a one-in-a-million lifetime cancer risk and is not a legal limit.

Much of Arizona’s arsenic is natural. A 2012 US Geological Survey study predicted that 43% of the area of basin-fill aquifers in the Southwest has arsenic at or above 10 ppb, concentrated in a belt of basins that includes parts of Arizona. A separate 2023 USGS study of 230 groundwater sites in the Grand Canyon region found 12% above the federal standard, likely from natural geothermal activity.

Six Arizona systems have an open violation under EPA’s Arsenic Rule, but all six are monitoring violations: missed or late sampling, not results over the limit. For health effects and treatment options, see our full guide to arsenic in tap water.

Other common concerns

• Disinfection byproducts: haloacetic acids (HAA9) and total trihalomethanes each appear for 12 of the 21 systems. These form when disinfectants react with organic matter in water. See disinfection byproducts explained.
• Chromium-6: listed for 8 systems, 6 of them groundwater systems. EPA does not have a separate limit for chromium-6. It regulates total chromium at 100 ppb, which includes chromium-6. See chromium-6 in tap water.
• PFAS: 4 systems list “PFAS contamination” (Tempe, Gilbert, Liberty Water LPSCO and Avondale), and all four grade F. See the EPA PFAS rule explained.
• Nitrate: listed for 2 systems, Queen Creek and EPCOR San Tan. See nitrate in tap water.

What the EPA records show

The 21 systems have 63 violation entries in total. Fifty-eight are monitoring or reporting entries, 2 are public notice entries, and 3 are health-based. All 63 are listed as open. The most common rules involved are the Stage 1 disinfection byproducts rule (10 systems), synthetic organic chemicals (7), the Revised Total Coliform Rule (6) and the Arsenic Rule (6).

The three health-based violations:

• EPCOR - Agua Fria (Surprise): an open treatment technique violation under the Revised Total Coliform Rule since August 2025.
• GW Santa Cruz Water Co (Maricopa): an open MCL violation under the Revised Total Coliform Rule since August 2025. Under that rule, the MCL relates to E. coli.
• Liberty Water LPSCO (Litchfield Park): an open treatment technique violation under the Ground Water Rule since December 2023.

Gilbert had the most persistent record, with violations in 11 of 12 quarters across nine rules, all monitoring or reporting. For how Arizona compares with other states on violations, see states ranked by drinking water violations.

What Arizona residents can do

1. Find your system on our Arizona page or search by ZIP code, and read its top concerns.
2. Check your arsenic number. Your utility’s Consumer Confidence Report lists the arsenic level it measured. Our guide on how to read your water quality report explains where to find it.
3. If you want to lower arsenic at home, CDC lists reverse osmosis among the home treatment options that can reduce it. Look for a system certified to NSF/ANSI 58 with a specific arsenic reduction claim, and confirm it in the certifier’s online listing. Our post on reverse osmosis vs. carbon filters explains the difference.
4. On a private well? EPA does not regulate private wells, so testing is up to you. See our well water testing guide.

If you are pregnant, preparing infant formula, or have a health condition, ask your doctor whether your water’s arsenic or nitrate level is a concern for you.

Note: utilities may have resolved issues since October 7, 2026. Check each utility’s EPA ECHO report or its latest Consumer Confidence Report for current status.

Sources

• University of Arizona: Where does our water come from? (citing ADWR, 2020)
• Central Arizona Project: Fact Sheet (August 2026)
• City of Phoenix: Water Supply Q&A
• City of Tucson: Drinking Water Distribution System
• NGWA (2009): Tucson’s Clearwater Program, recharge and recovery of surface water
• EPA: Chemical Contaminant Rules (Arsenic Rule)
• EPA: Chromium in Drinking Water
• OEHHA: Public Health Goal for Arsenic in Drinking Water (2004)
• USGS: Maps of Estimated Nitrate and Arsenic Concentrations in Basin-Fill Aquifers of the Southwestern United States (SIM 3234, 2012)
• USGS: Elevated arsenic in Grand Canyon region groundwater sites likely natural (2023)
• EPA: Private Drinking Water Wells
• CDC: About Home Water Treatment Systems
• EPA: Revised Total Coliform Rule
• EPA ECHO: Detailed Facility Reports (linked from each utility page)