Well water in Clark County, Ohio
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Testing recommended
tested well samples in Clark County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
2,231 test results across 15 contaminants from at least 63 wells, 1972 to 2020; chloride has the most at 774. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 39,741 people in Clark County get their drinking water from a private well, per USGS 2015 county water use. That is about 29% of residents.
Separately, the USGS national arsenic model estimates that 3% of the 39,741 people on private wells in Clark County draw water above 10 ug/L (the model's range is 3% to 4%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Clark 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 1972 to 2020 | 140 | 88% | 2.75 | 48.7 | 10 mg/L EPA limit | |
| Arsenic 1991 to 2020 | 63 | 43% | 0 | 10.3 | 10 ug/L EPA limit | |
| Fluoride 1972 to 2020 | 97 | 95% | 0.21 | 0.4 | 4 mg/L EPA limit | |
| Lead 1972 to 2020 | 80 | 15% | 0 | 0.78 | 15 ug/L EPA limit | |
| Copper 1991 to 2020 | 73 | 44% | 0 | 0.026 | 1.3 mg/L EPA limit | |
| Uranium 1999 to 2020 | 34 | 91% | 1.24 | 5 | 30 ug/L EPA limit | |
| Radium (226 + 228) 1999 to 2020 | 27 | 74% | 0.08 | 0.9 | 5 pCi/L EPA limit | |
| PFOA 2019 to 2020 | 18 | 11% | 0 | 1.2 | 4 ng/L EPA limit | |
| PFOS 2019 to 2020 | 18 | 6% | 0 | 1.9 | 4 ng/L EPA limit | |
| Chloride 1972 to 2020 | no limit | 774 | 100% | 21 | 183 | 250 mg/L nuisance level |
| Sodium 1972 to 2020 | no limit | 708 | 100% | 11 | 91.9 | 20 mg/L health guideline |
| Iron 1972 to 2020 | no limit | 89 | 54% | 4 | 2,590 | 300 ug/L nuisance level |
| Manganese 1972 to 2020 | no limit | 88 | 75% | 24.9 | 492 | 300 ug/L health guideline |
| Radon 1999 to 2013 | no limit | 15 | 100% | 340 | 1,390 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (7).
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 | 8%80 samples | 20%30 samples | 10%20 samples | 10%10 samples |
| Fluoride | 0%53 samples | 0%15 samples | 0%24 samples | n/a |
| Lead | 0%38 samples | 0%12 samples | 0%25 samples | n/a |
| Copper | 0%31 samples | 0%12 samples | 0%25 samples | n/a |
| Arsenic | 0%21 samples | 0%12 samples | 4%25 samples | n/a |
| Radium (226 + 228) | 0%12 samples | n/a | 0%13 samples | n/a |
Nitrate above the limit in Clark County fell from 20% of 30 samples in the 2000s to 10% of 20 in the 2010s.
Fluoride, lead, copper, arsenic 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 addressWhat this means
The contaminants most often above their limit here are nitrate (11% of 140 samples) and arsenic (2% of 63 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, Iron, and Manganese 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 Clark County
- 1Nitrate11% of 140 local samples were above the limit.
- 2Arsenic2% of 63 local samples were above the limit.
- 3RadonMedian local reading is 340 pCi/L.
- 4E. coliAbove the limit in 1 of 7 local samples; too few to quote a rate.
- 5ChlorideDetected in 100% of local samples.
- 6FluorideDetected in 95% of local samples.
- 7ManganeseDetected in 75% of local samples.
- 8Volatile organic compounds (VOCs)571 leaking underground storage tank sites on record locally.
- 9Metals panel35 hazardous waste sites on record locally.
Test your Clark County well for nitrate, arsenic and radon
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 $209Already 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 Ohio: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Clark County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Clark County
8,683 domestic wells in Clark County are on record with the state since 1970. 47% are drilled into bedrock, and the typical well is 86 feet deep (one in ten goes past 175 feet).
In a typical Clark County well, bedrock starts about 58 feet down, the median yield is 15 gallons per minute, <1% of wells yield under 3 gallons per minute and usually need a storage tank.
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 ODNR water well log search and choose Water Well.
- The log lists depth, depth to bedrock, casing, static water level, the pump test and the driller.
Ohio has required well logs since 1948, so most drilled wells have one.
The rock under Clark County
Silurian-Devonian aquifers
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 county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Ohio
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 Water Systems Program, Ohio Department of Health
- Laboratory Certification, Ohio EPA
Contamination sources on record in Clark County
Ohio EPA records 571 leaking underground storage tank sites and 35 hazardous waste sites in Clark County, among 624 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.
- 571
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 35
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 7
- lined landfills and transfer facilities
- 11
- other remediation projects
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
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
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 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 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 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.
Free, no obligation
Get on the list for a free in-home water test in Clark County
No water treatment company serves Clark 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 Clark County, and you get an email naming it first.
Common questions
How deep are wells in Clark County?
The typical domestic well in Clark County is 86 feet deep, based on 8,683 wells reported to the state since 1970. One in ten is deeper than 175 feet. 47% are drilled into bedrock.
Is there arsenic in well water in Clark County?
Arsenic was detected in 43% of 63 public well samples in Clark County, and 2% 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 Clark County?
The median radon level across 15 public samples in Clark County was 340 pCi/L, with a high of 1,390 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Clark 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 Clark County
9 towns have fewer than 30 public samples and are included in the Clark County totals above rather than shown separately: German township, Green township, Harmony township, Madison township, Mad River township, Pike township, Pleasant township, Springfield, Springfield township.
Counties near Clark 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 Ohio dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 2,231 samples in Clark 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 39,741 people on private wells in Clark 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.
- Ohio DNR water well logs: 10,369 well records in Clark County, 8,683 domestic. Water well logs filed with the Ohio Department of Natural Resources Division of Water Resources since 1948. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 17, 2026.
- Ohio EPA regulated sites: 624 regulated sites located in Clark County. Remediation sites, leaking underground storage tank releases (BUSTR) and landfills from the Ohio Environmental Protection Agency and the Division of State Fire Marshal. Retrieved September 17, 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.