Quick answer
About 242,000 people in Arizona (3.8% of residents) got their water from private wells in 2010, according to USGS estimates. Arizona Department of Health Services runs the state’s private well guidance. We didn’t find a free statewide well testing program in Arizona. Certified labs charge for each test, and some county health departments offer lower-cost bacteria and nitrate tests.
- People on private wells
- 242,037
- Share of residents
- 3.8%
- Rank among states
- 39th
- Well users modeled above 10 µg/L arsenic
- 28.4%
Where to get your well tested in Arizona
- Arizona Department of Health Services: Well Water Quality, the state’s guidance for private well owners.
- Well water testing in Arizona: what to test for and how to collect a sample.
- Certified laboratories in Arizona. Use a lab certified for drinking water, so results are reliable.
Free or low-cost testing
We didn’t find a free statewide program in Arizona. Certified labs charge per test; county health departments sometimes offer lower-cost bacteria and nitrate tests.
Mail-in lab kits are another option when no local lab is convenient. See well water test kits for what home kits can and can’t tell you.
What to test for
- Every year: total coliform bacteria and nitrate.
- Before buying equipment: pH, hardness, iron, manganese and, if there’s a smell, hydrogen sulfide.
- Based on location: arsenic, uranium and radon, PFAS, and lead in older plumbing.
USGS modeling estimates that about 28.4% of Arizona’s private well users have water above the 10 µg/L arsenic limit. Arsenic has no taste or smell, so include it in your first test.
Private wells by county
Estimated people relying on private wells in each Arizona county in 2010, the share of residents that represents, and the modeled share of well users with arsenic above 10 µg/L. These are USGS model estimates (2010 population), not measurements of any well. Arsenic is hidden for counties with fewer than 500 well users.
| County | People on wells | Share | Arsenic >10 µg/L |
|---|---|---|---|
| Maricopa County | 43,437 | 1.1% | 51.5% |
| Yavapai County | 41,067 | 19.5% | 39.2% |
| Pima County | 26,938 | 2.7% | 28.9% |
| Cochise County | 22,410 | 17.1% | 9.7% |
| Pinal County | 20,832 | 5.5% | 43.3% |
| Apache County | 16,238 | 22.7% | 10.7% |
| Navajo County | 13,945 | 13.0% | 11.1% |
| Mohave County | 11,483 | 5.7% | 15.5% |
| Yuma County | 10,832 | 5.5% | 16.1% |
| Gila County | 8,378 | 15.6% | 7.0% |
| Coconino County | 7,770 | 5.8% | 13.0% |
| La Paz County | 6,329 | 30.9% | 25.4% |
Show all 15 counties
| Graham County | 5,746 | 15.4% | 11.4% |
| Santa Cruz County | 4,635 | 9.8% | 6.4% |
| Greenlee County | 1,997 | 23.7% | 16.0% |
Counties with the highest modeled arsenic share: Maricopa County (51.5%), Pinal County (43.3%), Yavapai County (39.2%), Pima County (28.9%), La Paz County (25.4%).
After you get results
Enter your numbers in the test results tool to see what needs treating and in what order. The guide to reading a well water test explains units and limits.
Common questions
Does Arizona offer free well water testing?
We didn’t find a free statewide well testing program in Arizona. Certified labs charge for each test, and some county health departments offer lower-cost bacteria and nitrate tests.
Who oversees private wells in Arizona?
Arizona Department of Health Services (Well Water Quality) publishes guidance for private well owners. Private wells aren’t covered by the federal Safe Drinking Water Act, so testing and treatment are up to the owner.
How many people use private wells in Arizona?
USGS estimates about 242,000 people, or 3.8% of the population in 2010. That ranks 39th of the states covered by the estimate.
What should I test my well for in Arizona?
Test every year for total coliform bacteria and nitrate, plus pH, hardness, iron and manganese before buying equipment. Arsenic is a known concern in parts of Arizona, so add it to the first test.
Sources
- Arizona Department of Health Services: Well Water Quality
- Arizona Department of Health Services: well water testing
- Arizona certified laboratories
- USGS data release: domestic well locations and populations served, 2000 and 2010 (Johnson, Belitz and Lombard, 2019)
- CDC Environmental Public Health Tracking: private well water data (from USGS)