Well water in Knox County, Maine

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Testing recommended

private wells tested in Knox County had arsenic above the Maine guideline (10 ug/L), according to Maine CDC.

819 private wells tested in state summaries; 251 test results across 12 contaminants from at least 36 wells, 1984 to 2025; PFOA has the most at 36. Data refreshed September 15, 2026.

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

Maine DEP samples private wells near fields where sludge or septage was spread and near other known PFAS sources, and resamples detections. PFAS shares describe wells that were tested for a reason, not every well in the area. In that targeted sampling, 14% of 36 PFOA results in Knox County were above the EPA limit of 4 ng/L. In that targeted sampling, 11% of 36 PFOS results in Knox County were above the EPA limit of 4 ng/L.

An estimated 15,786 people in Knox County get their drinking water from a private well, per USGS 2015 county water use. That is about 40% of residents.

Separately, the USGS national arsenic model estimates that 6% of the 15,786 people on private wells in Knox County draw water above 10 ug/L (the model's range is 5% to 9%), from geology and well depth rather than local tests.

What homeowner tests found

Maine Tracking Network private well summaries: private wells tested and reported to the state. 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
Arsenic	17%	798	10 ug/L
Manganese	8%	633	300 ug/L
Uranium	2%	548	30 ug/L
Fluoride	<1%	819	2 mg/L
Nitrate	<1%	799	10 mg/L
Nitrite	<1%	798	1 mg/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Knox 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
Arsenic 2001 to 2007	100%	25	100%	86	310	10 ug/L EPA limit
PFOA 2022 to 2025	14%	36	56%	0.368	140	4 ng/L EPA limit
PFOS 2022 to 2025	11%	36	44%	0	31.3	4 ng/L EPA limit
Uranium 2006 to 2007	8%	12	75%	0.1	41	30 ug/L EPA limit
PFHxS 2022 to 2025	0%	36	36%	0	7.02	10 ng/L EPA limit
PFNA 2022 to 2025	0%	36	11%	0	1.95	10 ng/L EPA limit
Nitrate 1984 to 2007	0%	27	22%	0	1.3	10 mg/L EPA limit
Fluoride 2006 to 2007	0%	12	100%	0.5	1.1	4 mg/L EPA limit
Lead 2006 to 2007	0%	12	0%	0	0	15 ug/L EPA limit
Iron 1984 to 2007	no limit	15	87%	280	3,700	300 ug/L nuisance level

Sampled fewer than 10 times, too few to summarize: Chloride (3), Sodium (1).

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

Among homeowners in Knox County who sent a sample to the state lab, the health-based limits most often exceeded were arsenic (17% of 798 wells), uranium (2% of 548 wells), and fluoride (<1% of 819 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.

What to test for in Knox County

1
Arsenic
100% of 25 local samples were above the limit.
2
PFOA
14% of 36 local samples were above the limit.
3
PFOS
11% of 36 local samples were above the limit.
4
Uranium
8% of 12 local samples were above the limit.
5
Fluoride
<1% of 819 local wells tested were above the Maine guideline.
6
Nitrate
<1% of 799 local wells tested were above the Maine guideline.
7
Nitrite
<1% of 798 local wells tested were above the Maine guideline.
8
Coliform bacteria
Recommended for every private well, every year.
9
Volatile organic compounds (VOCs)
32 leaking underground storage tank sites on record locally.
10
PFAS
17 unlined landfills on record locally.
11
Metals panel
21 hazardous waste sites on record locally.

Test your Knox County well for arsenic, PFOA and PFOS

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 Maine: certified labs, state programs and prices.

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

Wells in Knox County

3,467 domestic wells in Knox County are on record with the state since 1970. 97% are drilled into bedrock, and the typical well is 200 feet deep (one in ten goes past 365 feet).

In a typical Knox County well, bedrock starts about 12 feet down, the median yield is 7 gallons per minute, 19% of wells yield under 3 gallons per minute and usually need a storage tank.

Bedrock wells are where arsenic, uranium and radon come from: the water sits in fractures in granite and metamorphic rock and picks up whatever the rock carries. That is why testing for those three matters more here than in a dug or gravel well.

483

1970s

252

1980s

433

1990s

459

2000s

308

2010s

779

2020s

Official help in Maine

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 Well Water, Maine CDC
Laboratory Accreditation, Maine CDC

Contamination sources on record in Knox County

Maine DEP records 32 leaking underground storage tank sites, 17 unlined landfills, and 21 hazardous waste sites in Knox County, among 162 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.

32: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
17: unlined landfillsOlder unlined landfills are a leading source of PFAS, VOCs and metals in nearby wells.
21: hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
92: other remediation projects

Treatment that fits the local profile

Arsenic

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

Manganese

Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis

PFOA

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

PFOS

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

Uranium

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

Iron

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

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 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 manganese

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 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.

Free, no obligation

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

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

Common questions

How deep are wells in Knox County?

The typical domestic well in Knox County is 200 feet deep, based on 3,467 wells reported to the state since 1970. One in ten is deeper than 365 feet. 97% are drilled into bedrock.

Is there arsenic in well water in Knox County?

Arsenic was detected in 100% of 25 public well samples in Knox County, and 100% 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 often should I test a private well in Knox 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.

Towns in Knox County

8 towns have fewer than 30 public samples and are included in the Knox County totals above rather than shown separately: Criehaven UT, Isle au Haut, Matinicus Isle plantation, Muscle Ridge Islands UT, North Haven, Rockland, Thomaston, Vinalhaven.

Counties near Knox 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 Maine dataset as CSV, every county and town, with the sources named.

Sources

Maine DEP PFAS investigation: 144 samples in Knox County. PFAS results for private wells sampled by the Maine Department of Environmental Protection. Retrieved September 3, 2026.
USGS Water Quality Portal: 107 samples in Knox 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.
Maine Tracking Network private well summaries: summaries for 6 contaminants in Knox County, up to 819 wells each. Town summaries of private well tests run by the Maine Health and Environmental Testing Laboratory, published by Maine CDC through the Maine Tracking Network. Shares are against Maine's guideline for each analyte (arsenic 10 ug/L, uranium 30 ug/L, fluoride 2 mg/L, manganese 0.3 mg/L, nitrate 10 mg/L, nitrite 1 mg/L). Towns with too few tests are suppressed (NR). Only the share above the guideline and wells tested are published; no medians. Retrieved September 3, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 15,786 people on private wells in Knox 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.
Maine Geological Survey well database: 3,654 well records in Knox County, 3,467 domestic. Well construction records reported to the Maine Geological Survey by licensed well drillers. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 3, 2026.
Maine DEP regulated sites: 162 regulated sites located in Knox County. Remediation sites, leaking underground storage tanks and closed municipal landfills from the Maine Department of Environmental Protection. Retrieved September 3, 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.