Arizona well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Arizona county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 15 counties
- Maricopa CountyWell users 43,400Arsenic about 51 in 100Nitrate 3.5 mg/L
- Yavapai CountyWell users 41,100Arsenic about 39 in 100Nitrate 0.7 mg/L
- Pima CountyWell users 26,900Arsenic about 29 in 100Nitrate 3.5 mg/L
- Cochise CountyWell users 22,400Arsenic about 10 in 100Nitrate 1.6 mg/L
- Pinal CountyWell users 20,800Arsenic about 43 in 100Nitrate 2.9 mg/L
- Apache CountyWell users 16,200Arsenic about 11 in 100Nitrate 0.3 mg/L
- Navajo CountyWell users 13,900Arsenic about 11 in 100Nitrate 0.2 mg/L
- Mohave CountyWell users 11,500Arsenic about 15 in 100Nitrate 1.3 mg/L
- Yuma CountyWell users 10,800Arsenic about 16 in 100Nitrate 0.8 mg/L
- Gila CountyWell users 8,400Arsenic about 7 in 100Nitrate 0.7 mg/L
- Coconino CountyWell users 7,800Arsenic about 13 in 100Nitrate 0.6 mg/L
- La Paz CountyWell users 6,300Arsenic about 25 in 100Nitrate 1.5 mg/L
- Graham CountyWell users 5,700Arsenic about 11 in 100Nitrate 1.4 mg/L
- Santa Cruz CountyWell users 4,600Arsenic about 6 in 100Nitrate 1.6 mg/L
- Greenlee CountyWell users 2,000Arsenic about 16 in 100Nitrate 0.9 mg/L
Each mark = 1 in 100 well users the model places above 10 µg/L arsenic (scale 0–10)10 mg/L nitrate: the federal limit (MCL) for public systems
- These figures describe the area, not your well. Only a lab test shows what’s in your water.
- CDC says the Well Water Index figures “do not describe risk to individual wells.” (CDC Tracking Network)
- The arsenic model is better at spotting low-arsenic areas than at confirming high ones.
- Well-user counts are 2010 USGS estimates; tract values are averages over each census tract.
- Total coliform bacteriaEvery year
- NitrateEvery year
- Total dissolved solidsEvery year
- pHEvery year
- ArsenicAsk your local health department
EPA: Private Drinking Water Wells · CDC: Guidelines for Testing Well Water
Use a state-certified lab
Arizona Department of Health Services, Office of Laboratory Licensure & Certification lists the laboratories certified to test drinking water in Arizona.
Screening tells you if something is worth a closer look
A lab result is the number you can act on.
As an Amazon Associate, PurityMap earns from qualifying purchases. Affiliate disclosure
Lab-certified results
ETR Labs Basic Water Quality Test Kit
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
- Analyzed by Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638
- Turnaround: 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Screening: quick check, not lab-grade
Watersafe Drinking Water Test Kit
Silver Lake Research
Lead, bacteria, nitrate, copper, iron, chlorine, hardness and pH
- Turnaround: Minutes; the bacteria test can take up to 48 hours
What it can't tell you: Each test gives a yes/no or a rough range, not a lab number, and it cannot detect PFAS or arsenic.
A mail-in kit’s lab is accredited (ISO/IEC 17025) but may not be certified by your state. For a home sale, a loan, or a health-department follow-up, use a state-certified lab.
Arizona well water
Sources: CDC Well Water Index (2024) · USGS arsenic and nitrate models · USGS domestic well populations · EPA and CDC testing guidance. Data last updated 2026-10-08. All sources →
How many people use private wells in Arizona?
About 242,000 people across 15 Arizona counties, by the USGS 2010 estimate. USGS models place about 68,800 of them in areas where wells are likely to be above the 10 µg/L arsenic limit. These are area estimates, not well results.
Are private wells regulated in Arizona?
The quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. (EPA) Testing and treatment are the owner's responsibility.
Where can I get my well tested in Arizona?
Arizona Department of Health Services, Office of Laboratory Licensure & Certification keeps the list of laboratories certified to test drinking water in Arizona. Only use laboratories that are certified to do drinking water testing. (EPA)