Well water in Maricopa County, Arizona

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Testing strongly recommended

tested well samples in Maricopa County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.

37,925 test results across 14 contaminants from at least 2,335 wells, 1920 to 2026; chloride has the most at 8,920. Data refreshed September 15, 2026.

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

An estimated 42,440 people in Maricopa County get their drinking water from a private well, per USGS 2015 county water use. That is about 1% of residents.

Separately, the USGS national arsenic model estimates that 9% of the 42,440 people on private wells in Maricopa County draw water above 10 ug/L (the model's range is 7% to 11%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Maricopa 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
Nitrate 1923 to 2026	48%	8,723	99%	9.4	945	10 mg/L EPA limit
PFOA 2021 to 2026	40%	242	70%	2.22	91.9	4 ng/L EPA limit
Arsenic 1966 to 2026	28%	1,154	86%	6	160	10 ug/L EPA limit
Fluoride 1940 to 2026	19%	3,862	99%	1.4	1,280	4 mg/L EPA limit
Uranium 1958 to 2026	14%	265	97%	4.9	122	30 ug/L EPA limit
E. coli 1998 to 2022	2%	91	2%	0	120	0 MPN/100mL EPA limit
Lead 1968 to 2026	<1%	1,175	22%	0	500	15 ug/L EPA limit
Copper 1933 to 2026	<1%	1,053	37%	0	29	1.3 mg/L EPA limit
Radium (226 + 228) 1989 to 2026	0%	262	51%	0.015	2.9	5 pCi/L EPA limit
Chloride 1920 to 2026	no limit	8,920	100%	362	190,000	250 mg/L nuisance level
Sodium 1923 to 2026	no limit	7,786	100%	258	13,900	20 mg/L health guideline
Iron 1946 to 2026	no limit	2,163	55%	0	9,300	300 ug/L nuisance level
Manganese 1957 to 2026	no limit	2,035	36%	0	6,900	300 ug/L health guideline
Radon 1989 to 2017	no limit	194	100%	523	3,956	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
Nitrate	50%7,790 samples	39%358 samples	21%174 samples	18%401 samples
Fluoride	20%3,292 samples	11%250 samples	16%212 samples	16%108 samples
Lead	<1%632 samples	<1%188 samples	<1%246 samples	<1%109 samples
Arsenic	25%616 samples	22%200 samples	32%212 samples	42%126 samples
Copper	<1%554 samples	0%188 samples	0%212 samples	0%99 samples
Uranium	17%115 samples	6%50 samples	4%48 samples	25%52 samples

Arsenic above the limit in Maricopa County rose from 32% of 212 samples in the 2010s to 42% of 126 in the 2020s.

Uranium above the limit in Maricopa County rose from 4% of 48 samples in the 2010s to 25% of 52 in the 2020s.

Nitrate, fluoride, lead, copper 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 nitrate (48% of 8,723 samples), pfoa (40% of 242 samples), and arsenic (28% of 1,154 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 Maricopa County

1
Nitrate
48% of 8,723 local samples were above the limit.
2
PFOA
40% of 242 local samples were above the limit.
3
Arsenic
28% of 1,154 local samples were above the limit.
4
Fluoride
19% of 3,862 local samples were above the limit.
5
Uranium
14% of 265 local samples were above the limit.
6
E. coli
2% of 91 local samples were above the limit.
7
Lead
<1% of 1,175 local samples were above the limit.
8
Volatile organic compounds (VOCs)
2,424 leaking underground storage tank sites on record locally.

Test your Maricopa County well for nitrate, PFOA and arsenic

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 Maricopa County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

Wells in Maricopa County

23,099 domestic wells in Maricopa County are on record with the state since 1970. the typical well is 400 feet deep (one in ten goes past 705 feet).

In a typical Maricopa County well, the median yield is 15 gallons per minute, 2% of wells yield under 3 gallons per minute and usually need a storage tank.

1,378

1970s

2,100

1980s

2,688

1990s

4,313

2000s

1,298

2010s

594

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 Maricopa 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 Maricopa County

ADEQ records 2,424 leaking underground storage tank sites in Maricopa County, among 2,432 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.

2,424: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
8: lined landfills and transfer facilities

Treatment that fits the local profile

Nitrate

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

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

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 nitrate

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

For nitrate

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 PFOA

Aquasana Claryum 3-Stage under-sink filter

under-sink or countertop, about $175

Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.

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 HealthShield whole-house filter

whole-house, at the point of entry, about $2,099

Whole-house carbon system the maker certifies to reduce PFAS (PFOA and PFOS) and VOCs at every tap; a UV option adds bacteria protection.

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 Maricopa County

No water treatment company serves Maricopa 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 Maricopa County, and you get an email naming it first.

Common questions

How deep are wells in Maricopa County?

The typical domestic well in Maricopa County is 400 feet deep, based on 23,099 wells reported to the state since 1970. One in ten is deeper than 705 feet.

Is there arsenic in well water in Maricopa County?

Arsenic was detected in 86% of 1,154 public well samples in Maricopa County, and 28% 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 Maricopa County?

The median radon level across 194 public samples in Maricopa County was 523 pCi/L, with a high of 3,956 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Maricopa 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 Maricopa 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: 37,925 samples in Maricopa 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 42,440 people on private wells in Maricopa 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): 50,860 well records in Maricopa County, 23,099 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: 2,432 regulated sites located in Maricopa 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.