Arsenic, nitrate and uranium are widespread in Maricopa County wells.
3 widespread, 1 worth checking, 3 rare out of 7 health checks.
From 739 wells tested in Maricopa County since 2000; your own well needs its own test. How to read this
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
About 1 in 30 people 146,769 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Deep wells: fewer surface germs, more minerals from the rock.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how Maricopa County compares with Arizona and the counties around it.
Each result puts Maricopa County next to the 6 counties that border it, on the chart's 0 to 50% scale.
These 3 are widespread in Maricopa County wells.
Arsenic140 of 416 wells over
Nitrate109 of 451 wells over
Uranium16 of 96 wells over
Too few tested to show: Gila, La Paz, Pinal, Yuma.
This one is worth checking in Maricopa County.
These 3 are rare in Maricopa County.
Manganese21 of 439 wells over
Lead5 of 376 wells over
Radon in water0 of 106 wells over
Coliform bacteria turned up in 25 of 82 tested Maricopa County wells, so test for it every year.
Coliform bacteria25 of 82 wells had it
Too few tested to show: Gila, La Paz, Pinal, Yuma.
E. coli6 of 86 wells had it
Too few tested to show: Gila, La Paz, Pinal, Yuma.
E. coli means human or animal waste is getting in, so if a test of your Maricopa County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 79 of 488 tested wells, and it isn't a health risk.
Iron stains79 of 488 wells had it
About 3 in 10 of the 739 wells tested in Maricopa County have a test from 2020 or later.
With 224 wells tested since 2020, age matters less here than who did the testing and why.
Most Maricopa County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 5 things to check in Maricopa County.
- Bacteria
- Nitrate
- Arsenic
- Uranium
- Fluoride
What Arizona offers well owners
- Free testingWe didn't find a free program for all of Arizona. Arizona's private well page
- Certified labsArizona's list of certified labs
- Well recordsWe didn't find an online search.
Half the household wells here are shallower than 400 feet.
That comes from 14,896 household wells in Arizona's drilling records. Most wells of every kind here are 180 to 600 feet deep. Wells as deep as Maricopa County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here go deeper than in 13 of the 14 other Arizona counties with enough drilling records.
How to find your own well's depth
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Maricopa County.
Maricopa County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 42 town water systems in Maricopa County test for PFAS. 8 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 56 ng/L of PFOS. Only 178 wells in Maricopa County have public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Maricopa County
Is well water in Maricopa County safe to drink?
140 of 416 wells tested in Maricopa County had arsenic over the limit, about 1 in 3. Across Arizona it's about 1 in 4. That's a bigger share than in 13 of the 14 other Arizona counties with 10 or more tested wells. So test your own well for arsenic before you count on it.
Where can I get my well tested in Maricopa County?
Use a lab Arizona has certified for drinking water. Arizona's list is linked above, in the box about testing. Ask for bacteria, nitrate, arsenic, uranium and fluoride, the tests that matter most in Maricopa County.
How deep are wells in Maricopa County?
Half the household wells here are shallower than 400 feet. Typical household wells here go deeper than in 13 of the 14 other Arizona counties with enough drilling records.
How does Maricopa County compare with the counties around it?
For arsenic, the share of tested wells over the limit: 1 of the 6 neighboring counties with data had a higher share than Maricopa County, at 34%. Yuma had the most, at 60%. Groundwater doesn't stop at county lines, so Yuma's 60% is worth knowing about if you live near it.
How often should I test my well in Maricopa County?
In Maricopa County, 25 of 82 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
If you buy something through our links, we may earn a commission. We'd recommend the same thing either way, and we'll tell you when a free option exists. How we make money
Where the Maricopa County numbers come from
- People on wells: 146,769 in Maricopa County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 4,910 well water samples from 739 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2026.
- Well depths: 14,896 Arizona drilling records for Maricopa County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 6 counties that share a border with Maricopa County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 42 town water systems in Maricopa County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Maricopa County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Department of Health Services, checked November 1, 2026.