Well water in Mercer County, Pennsylvania

1in2

Testing strongly recommended

private wells tested between 2007 and 2025 in Mercer County had total coliform above the EPA limit (0 MPN/100mL), according to the Penn State water testing lab.

279 private wells tested 2007 to 2025 in state summaries; 720 test results across 14 contaminants from at least 106 wells, 1928 to 2026; nitrate has the most at 120. Data refreshed September 16, 2026.

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

These are samples homeowners paid to send to the Penn State lab, often because of a suspected problem, so shares above the limit run higher than a random survey would find.

An estimated 53,453 people in Mercer County get their drinking water from a private well, per USGS 2015 county water use. That is about 47% of residents.

Separately, the USGS national arsenic model estimates that 8% of the 53,453 people on private wells in Mercer County draw water above 10 ug/L (the model's range is 4% to 13%), from geology and well depth rather than local tests.

What homeowner tests found

Penn State Agricultural Analytical Services Lab drinking water summaries: private wells tested and reported to the state, 2007 to 2025. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.

Contaminant	Above state level	Wells tested	Median	Highest	State level
Total coliform	43%	279		201	0 MPN/100mL
Iron	28%	97	100	8,800	300 ug/L
Manganese	27%	106	10	4,730	50 ug/L
E. coli	7%	279		201	0 MPN/100mL
Lead (first draw)	7%	92		53	15 ug/L
Chloride	7%	46	17.2	479	250 mg/L
Arsenic	6%	98		34	10 ug/L
Nitrate + nitrite as N	5%	132	0.4	12.2	10 mg/L
Copper	0%	120	0.01	0.43	1.3 mg/L
Sodium		15	60.6	208

What individual samples found

Each row summarizes every public sample for that contaminant inside Mercer 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 2023 to 2026	8%	13	77%	4.1	14.5	10 ug/L EPA limit
Nitrate 1928 to 2026	2%	120	88%	0.2	35	10 mg/L EPA limit
Fluoride 1937 to 2026	0%	101	99%	0.2	3	4 mg/L EPA limit
Copper 2023 to 2026	0%	13	31%	0	0.009	1.3 mg/L EPA limit
Lead 2023 to 2026	0%	13	31%	0	0.45	15 ug/L EPA limit
Chloride 1928 to 2026	no limit	112	100%	4.65	2,820	250 mg/L nuisance level
Iron 1928 to 2026	no limit	112	98%	380	33,000	300 ug/L nuisance level
Sodium 1928 to 2026	no limit	109	100%	8	1,690	20 mg/L health guideline
Manganese 1937 to 2026	no limit	105	100%	49	1,400	300 ug/L health guideline

Sampled fewer than 10 times, too few to summarize: Uranium (8), E. coli (6), PFOA (1), PFOS (1), Radon (6).

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	2%100 samples	n/a	n/a	0%20 samples
Fluoride	0%89 samples	n/a	n/a	0%12 samples

Nitrate has 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

Among homeowners in Mercer County who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (43% of 279 wells), E. coli (7% of 279 wells), and lead (7% of 92 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 and manganese exceed the state's advisory level in a sizable share of wells; these are mostly a taste, staining or diet issue rather than a toxicity one.

What to test for in Mercer County

1
Total coliform
43% of 279 local wells tested were above the EPA limit.
2
Arsenic
8% of 13 local samples were above the limit.
3
E. coli
7% of 279 local wells tested were above the EPA limit.
4
Lead
7% of 92 local wells tested were above the EPA limit.
5
Nitrate
5% of 132 local wells tested were above the EPA limit.
6
Radon
Median local reading is 170 pCi/L.
7
Iron
28% of 97 local wells tested were above the EPA secondary standard.
8
Manganese
27% of 106 local wells tested were above the EPA secondary standard.

Test your Mercer County well for total coliform, arsenic and E. coli

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 Pennsylvania: certified labs, state programs and prices.

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

Wells in Mercer County

6,237 domestic wells in Mercer County are on record with the state. 93% are drilled into bedrock, and the typical well is 95 feet deep (one in ten goes past 187 feet).

In a typical Mercer County well, bedrock starts about 28 feet down, the median yield is 20 gallons per minute, <1% 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.

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 PaGWIS (Pennsylvania Geological Survey) and choose Water Well.
The record lists depth, depth to bedrock, yield and use; drillers have reported new wells to the state since 1966.

Pennsylvania has no private well construction standard and does not require testing, so many older wells have no record at all.

The rock under Mercer County

Mississippian aquifers

Sandstone and carbonate-rock. Layered sandstone and limestone means a well may draw from either. Hardness and iron are routine, and the limestone layers can carry bacteria and nitrate from the surface quickly, so test for both yearly.

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 Pennsylvania

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 Wells, PA DEP
Laboratory Accreditation Program, PA DEP

Treatment that fits the local profile

Total coliform

Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system

E. coli

Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system

Lead

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

Arsenic

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

Nitrate

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

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 total coliform

Aquasana Rhino Well Water with UV

whole-house, at the point of entry, about $2,871

Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.

For E. coli

UV disinfection system

whole-house, at the point of entry, about $900

Fix the well cap and casing first; UV keeps bacteria from returning.

For lead

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

For lead

Acid neutralizing filter

whole-house, at the point of entry, about $1,200

Raises pH so plumbing stops leaching lead and copper.

For lead

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 Mercer County

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

Common questions

How deep are wells in Mercer County?

The typical domestic well in Mercer County is 95 feet deep, based on 6,237 wells reported to the state. One in ten is deeper than 187 feet. 93% are drilled into bedrock.

Is there arsenic in well water in Mercer County?

Arsenic was detected in 77% of 13 public well samples in Mercer County, and 8% 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 Mercer 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 Mercer County

48 towns have fewer than 30 public samples and are included in the Mercer County totals above rather than shown separately: Clark borough, Coolspring township, Deer Creek township, Delaware township, East Lackawannock township, Fairview township, Farrell, Findley township, Fredonia borough, French Creek township, Greene township, Greenville borough, Grove City borough, Hempfield township, Hermitage, Jackson Center borough, Jackson township, Jamestown borough, Jefferson township, Lackawannock township, Lake township, Liberty township, Mercer borough, Mill Creek township, New Lebanon borough, New Vernon township, Otter Creek township, Perry township, Pine township, Pymatuning township, Salem township, Sandy Creek township, Sandy Lake borough, Sandy Lake township, Sharon, Sharpsville borough, Sheakleyville borough, Shenango township, South Pymatuning township, Springfield township, Stoneboro borough, Sugar Grove township, West Middlesex borough, West Salem township, Wheatland borough, Wilmington township, Wolf Creek township, Worth township.

Counties near Mercer 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 Pennsylvania dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 720 samples in Mercer 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.
Penn State Agricultural Analytical Services Lab drinking water summaries: summaries for 10 contaminants in Mercer County, up to 279 wells each. County summaries of private water samples tested by the Penn State Agricultural Analytical Services Laboratory since 2007, published by the College of Agricultural Sciences. Counts are samples, not distinct wells. Shares are against the standard the lab prints: the EPA maximum contaminant level, or the secondary standard for iron, manganese and chloride. Lead is the first-draw result. Medians printed as 0.00 are stored as null because the lab rounds to two decimals. Retrieved September 16, 2026.
USGS national arsenic model (Ayotte 2017): estimated share of 53,453 people on private wells in Mercer 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.
Pennsylvania Groundwater Information System (PaGWIS) wells: 8,143 well records in Mercer County, 6,237 domestic. Water well records from the Pennsylvania Groundwater Information System, Pennsylvania Geological Survey (DCNR). Only aggregates are shown; owner names and addresses are never stored. Retrieved September 16, 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.