Well water in Pima County, Arizona

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Testing strongly recommended

tested well samples in Pima County exceeded the EPA limit for PFOA (4 ng/L), based on public data from USGS Water Quality Portal.

11,746 test results across 14 contaminants from at least 1,156 wells, 1917 to 2026; chloride has the most at 1,946. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

An estimated 20,680 people in Pima County get their drinking water from a private well, per USGS 2015 county water use. That is about 2% of residents.

Separately, the USGS national arsenic model estimates that 3% of the 20,680 people on private wells in Pima County draw water above 10 ug/L (the model's range is 2% to 3%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Pima County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.

Contaminant	Above limit	Samples	Detected	Median	Highest	Limit
PFOA 2024 to 2026	50%	136	82%	4.05	76	4 ng/L EPA limit
Arsenic 1972 to 2024	15%	762	44%	0	960	10 ug/L EPA limit
Nitrate 1917 to 2026	10%	1,688	94%	2	690	10 mg/L EPA limit
Fluoride 1934 to 2024	6%	1,845	99%	0.5	54	4 mg/L EPA limit
Uranium 1976 to 2024	5%	143	97%	3.8	63	30 ug/L EPA limit
Radium (226 + 228) 1994 to 2013	3%	37	38%	0	29	5 pCi/L EPA limit
Lead 1972 to 2024	<1%	630	16%	0	700	15 ug/L EPA limit
Copper 1956 to 2024	<1%	822	34%	0	46	1.3 mg/L EPA limit
E. coli 2013 to 2023	0%	11	0%	0	0	0 MPN/100mL EPA limit
Chloride 1917 to 2026	no limit	1,946	99%	18	2,110	250 mg/L nuisance level
Sodium 1917 to 2024	no limit	1,281	100%	45	1,400	20 mg/L health guideline
Iron 1917 to 2024	no limit	1,275	62%	0	54,000	300 ug/L nuisance level
Manganese 1971 to 2024	no limit	1,069	32%	0	5,100	300 ug/L health guideline
Radon 1989 to 2017	no limit	101	99%	480	84,009	2,000 pCi/L health guideline

Over time

Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.

Contaminant	before 2000	2000s	2010s	2020s
Fluoride	6%1,705 samples	4%103 samples	21%28 samples	n/a
Nitrate	10%1,531 samples	21%73 samples	15%34 samples	2%50 samples
Copper	<1%707 samples	0%78 samples	0%28 samples	n/a
Arsenic	16%647 samples	7%75 samples	32%28 samples	8%12 samples
Lead	<1%515 samples	0%78 samples	0%28 samples	n/a
Uranium	4%114 samples	n/a	0%15 samples	n/a

Fluoride above the limit in Pima County rose from 4% of 103 samples in the 2000s to 21% of 28 in the 2010s.

Nitrate above the limit in Pima County fell from 15% of 34 samples in the 2010s to 2% of 50 in the 2020s.

Arsenic above the limit in Pima County rose from 7% of 75 samples in the 2000s to 32% of 28 in the 2010s.

Copper, lead have held within a few points between the two most recent periods with enough samples.

Closer than the county

See the sampled wells near your address

The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.

Check my address

What this means

The contaminants most often above their limit here are pfoa (50% of 136 samples), arsenic (15% of 762 samples), and nitrate (10% of 1,688 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.

Chloride and Iron are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.

What to test for in Pima County

1
PFOA
50% of 136 local samples were above the limit.
2
Arsenic
15% of 762 local samples were above the limit.
3
Nitrate
10% of 1,688 local samples were above the limit.
4
Fluoride
6% of 1,845 local samples were above the limit.
5
Uranium
5% of 143 local samples were above the limit.
6
Radium (226 + 228)
3% of 37 local samples were above the limit.
7
Lead
<1% of 630 local samples were above the limit.
8
Volatile organic compounds (VOCs)
732 leaking underground storage tank sites on record locally.

Test your Pima County well for PFOA, arsenic and nitrate

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209 Already tested? Upload the report

Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.

Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.

Where to get a well tested in Arizona: certified labs, state programs and prices.

Already have results back? Get your lab report read against the Pima County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

Wells in Pima County

10,928 domestic wells in Pima County are on record with the state since 1970. the typical well is 350 feet deep (one in ten goes past 680 feet).

In a typical Pima County well, the median yield is 18 gallons per minute, 3% of wells yield under 3 gallons per minute and usually need a storage tank.

983

1970s

1,184

1980s

1,411

1990s

1,264

2000s

268

2010s

153

2020s

Find your own well's report

The state keeps the driller's report for most wells drilled since 1984. It tells you how deep your well is, where bedrock starts, and how much water it makes, which decides what treatment can work.

Open ADWR Wells55 registry and choose Water Well.
The record lists depth, water level, casing depth and the tested rate, plus a link to the drilling log.

Arizona has registered wells since 1980; earlier wells often have no record.

The rock under Pima County

Basin and Range basin-fill aquifers

Unconsolidated sand and gravel. Wells in sand and gravel are usually shallow and productive, and they recharge quickly from the surface. That makes them the most exposed to nitrate, bacteria and anything spilled nearby, and the least likely to carry arsenic or radon from the rock.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.

Official help in Arizona

Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.

Well Water, ADHS
Licensed Commercial Drinking Water Laboratories, ADHS

Contamination sources on record in Pima County

ADEQ records 732 leaking underground storage tank sites in Pima County, among 737 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.

732: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
5: lined landfills and transfer facilities

Treatment that fits the local profile

PFOA

Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange

Arsenic

Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange

Nitrate

Point-of-use reverse osmosis; Anion exchange; Distillation

Fluoride

Point-of-use reverse osmosis; Activated alumina; Distillation

Uranium

Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange

Systems we would look at first

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For PFOA

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For PFOA

Whole-house PFAS carbon system

whole-house, at the point of entry, about $3,000

Granular activated carbon certified to NSF/ANSI 53 for PFOA and PFOS; replace media on schedule.

For PFOA

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

For arsenic

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

Free, no obligation

Get on the list for a free in-home water test in Pima County

No water treatment company serves Pima County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Pima County, and you get an email naming it first.

Common questions

How deep are wells in Pima County?

The typical domestic well in Pima County is 350 feet deep, based on 10,928 wells reported to the state since 1970. One in ten is deeper than 680 feet.

Is there arsenic in well water in Pima County?

Arsenic was detected in 44% of 762 public well samples in Pima County, and 15% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.

How high is radon in well water in Pima County?

The median radon level across 101 public samples in Pima County was 480 pCi/L, with a high of 84,009 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Pima County?

Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.

Counties near Pima County

Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.

Want the numbers themselves? Download the Arizona dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 11,746 samples in Pima County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 20,680 people on private wells in Pima County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
Arizona ADWR well registry (Wells55): 24,322 well records in Pima County, 10,928 domestic. Registered wells from the Arizona Department of Water Resources Wells55 registry. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 18, 2026.
ADEQ regulated sites: 737 regulated sites located in Pima County. Leaking underground storage tank sites and municipal landfills from the Arizona Department of Environmental Quality. Retrieved September 18, 2026.

Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.