Well water in Missouri

In Missouri, 3% of 15,041 private wells tested between 2010 and 2023 had lead above the EPA limit (15 ug/L), according to Missouri DHSS.

The strongest signal is arsenic: 13% of 2,937 local samples were above the limit, too few samples to carry the headline but first on the test list below.

15,041 private wells tested 2010 to 2023 in state summaries; 48,836 test results across 15 contaminants from at least 3,398 wells, 1892 to 2026; nitrate has the most at 11,815. Data refreshed September 15, 2026.

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

Missouri does not require private well testing, so these are samples homeowners chose to send to the state lab, often after a problem; shares above the limit run higher than a random survey would find.

An estimated 821,343 people in Missouri get their drinking water from a private well, per USGS 2015 county water use.

Separately, the USGS national arsenic model estimates that 1% of the 821,343 people on private wells in Missouri draw water above 10 ug/L (the model's range is <1% to 2%), from geology and well depth rather than local tests.

What homeowner tests found

Missouri DHSS private well sampling summaries: private wells tested and reported to the state, 2010 to 2023. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA. County and state figures combine the town summaries, weighted by wells tested; medians are not combined.

Contaminant	Above state level	Wells tested	State level
Iron	12%	10,561	300 ug/L
Lead	3%	15,041	15 ug/L
Nitrate	2%	11,532	10 mg/L
Arsenic	1%	6,973	10 ug/L
Chloride	<1%	10,678	250 mg/L
Fluoride	<1%	10,575	4 mg/L
Uranium	<1%	7,056	30 ug/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Missouri. 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
Arsenic 1970 to 2026	13%	2,937	48%	0	405	10 ug/L EPA limit
PFOA 2022 to 2026	9%	53	11%	0	7.1	4 ng/L EPA limit
Nitrate 1913 to 2026	6%	11,815	54%	0	4,380	10 mg/L EPA limit
PFOS 2022 to 2026	4%	53	4%	0	15.8	4 ng/L EPA limit
Lead 1924 to 2026	4%	2,785	27%	0	2,000	15 ug/L EPA limit
Uranium 1980 to 2026	2%	951	78%	0.227	14,000	30 ug/L EPA limit
E. coli 1999 to 2018	2%	184	2%	0	170	0 MPN/100mL EPA limit
Fluoride 1921 to 2026	<1%	5,381	88%	0.21	160	4 mg/L EPA limit
Copper 1940 to 2026	0%	2,655	32%	0	0.164	1.3 mg/L EPA limit
Radium (226 + 228) 1987 to 2018	0%	284	78%	0.39	4.9	5 pCi/L EPA limit
Iron 1901 to 2026	no limit	6,223	88%	300	490,000	300 ug/L nuisance level
Sodium 1892 to 2026	no limit	5,989	100%	17	14,000	20 mg/L health guideline
Manganese 1901 to 2026	no limit	4,728	90%	60	32,000	300 ug/L health guideline
Chloride 1892 to 2026	no limit	4,688	100%	10.1	50,000	250 mg/L nuisance level
Radon 1993 to 2018	no limit	110	100%	170	2,060	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	9%7,632 samples	1%2,616 samples	2%969 samples	2%598 samples
Fluoride	1%3,511 samples	<1%1,104 samples	0%475 samples	0%291 samples
Arsenic	11%1,727 samples	17%726 samples	13%314 samples	15%170 samples
Lead	6%1,575 samples	<1%726 samples	0%314 samples	0%170 samples
Copper	0%1,445 samples	0%726 samples	0%314 samples	0%170 samples
Uranium	6%306 samples	<1%171 samples	0%304 samples	0%170 samples

Nitrate, fluoride, arsenic, lead, copper, uranium have held within a few points between the two most recent periods with enough samples.

What this means

Among homeowners in Missouri who sent a sample to the state lab, the health-based limits most often exceeded were lead (3% of 15,041 wells), nitrate (2% of 11,532 wells), and arsenic (1% of 6,973 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.

Iron exceeds the state's advisory level in a sizable share of wells; this is mostly a taste, staining or diet issue rather than a toxicity one.

What to test for in Missouri

1
Arsenic
13% of 2,937 local samples were above the limit.
2
PFOA
9% of 53 local samples were above the limit.
3
Nitrate
6% of 11,815 local samples were above the limit.
4
PFOS
4% of 53 local samples were above the limit.
5
Lead
4% of 2,785 local samples were above the limit.
6
Uranium
2% of 951 local samples were above the limit.
7
E. coli
2% of 184 local samples were above the limit.
8
Fluoride
<1% of 10,575 local wells tested were above the EPA limit.
9
Volatile organic compounds (VOCs)
35 leaking underground storage tank sites on record locally.
10
Metals panel
1,110 hazardous waste sites on record locally.

Test your Missouri well for arsenic, PFOA 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 Missouri: certified labs, state programs and prices.

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

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Send me the Missouri report

The numbers above, which tests to order and where, and the treatment that fits the local profile, in one email.

Wells in Missouri

167,223 domestic wells in Missouri are on record with the state since 1977. the typical well is 346 feet deep (one in ten goes past 580 feet).

In a typical Missouri well, the median yield is 30 gallons per minute, <1% of wells yield under 3 gallons per minute and usually need a storage tank.

13,480

1980s

52,415

1990s

60,407

2000s

31,276

2010s

8,838

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 Missouri DNR WIMS and choose Water Well.
The certification record lists total depth, casing length, static water level, yield and the driller.

Missouri has required certification of new private wells since 1987, so a well drilled before then usually has no record.

The rock under Missouri

Ozark Plateaus aquifer system

Carbonate-rock. Limestone and dolomite move water through cracks and solution channels, sometimes very fast. Bacteria and nitrate can travel from the surface to a well in days, so annual bacteria testing matters more here than most places; hardness is a given.

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

Official help in Missouri

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.

Private Drinking Water, Missouri DHSS
Certified Laboratories, Missouri DNR

Contamination sources on record in Missouri

Missouri DNR records 35 leaking underground storage tank sites and 1,110 hazardous waste sites in Missouri, among 3,346 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.

35: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
1,110: hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
1,833: registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
276: lined landfills and transfer facilities
92: other solid waste facilities

Treatment that fits the local profile

Iron

Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration

Arsenic

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

PFOA

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

Nitrate

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

PFOS

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

Lead

Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching

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 iron

Iron and manganese oxidizing filter

whole-house, at the point of entry, about $1,800

Air-injection or greensand media; fixes staining at the source.

For arsenic

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

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.

For arsenic

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.

Common questions

How deep are wells in Missouri?

The typical domestic well in Missouri is 346 feet deep, based on 167,223 wells reported to the state since 1977. One in ten is deeper than 580 feet.

Is there arsenic in well water in Missouri?

Arsenic was detected in 48% of 2,937 public well samples in Missouri, and 13% 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 Missouri?

The median radon level across 110 public samples in Missouri was 170 pCi/L, with a high of 2,060 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Missouri?

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 in Missouri

8 counties have fewer than 30 public samples and are included in the Missouri totals above rather than shown separately: Harrison, Linn, Mercer, Putnam, Schuyler, Scotland, Sullivan, Worth.

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

Sources

USGS Water Quality Portal: 48,836 samples in Missouri. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
Missouri DHSS private well sampling summaries: summaries for 7 contaminants in Missouri, up to 15,041 wells each. County summaries of private well samples analyzed by the Missouri State Public Health Laboratory, 2010 to 2023, published by the Missouri Department of Health and Senior Services. Counts are samples, not distinct wells. Shares are against the EPA maximum contaminant level, or the EPA secondary standard for chloride and iron. Counties with fewer than 20 samples are flagged unreliable by DHSS and are kept here with their counts so the threshold rule can judge them. Barium, sulfate and zinc layers exist but have no contaminant page yet. Retrieved September 15, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 821,343 people on private wells in Missouri 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.
Missouri DNR certified well records: 290,786 well records in Missouri, 167,223 domestic. Well certification records from the Missouri Department of Natural Resources Wellhead Information Management System (WIMS), published through MSDIS. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 15, 2026.
Missouri DNR regulated sites: 3,346 regulated sites located in Missouri. Permitted solid waste facilities, and leaking tank, underground tank and hazardous waste sites from the historical CARES potential contaminant site inventory, Missouri Department of Natural Resources. Retrieved September 15, 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.