Well water in Onslow County, North Carolina
In Onslow County, 3% of 234 private wells tested between 1998 and 2019 had lead above the North Carolina groundwater standard (15 ug/L), according to the NC State Laboratory of Public Health (NCWELL).
The strongest signal is nitrate: 11% of 97 local samples were above the limit, too few samples to carry the headline but first on the test list below.
234 private wells tested 1998 to 2019 in state summaries; 475 test results across 15 contaminants from at least 51 wells, 1941 to 2024; nitrate has the most at 97. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 16,175 people in Onslow County get their drinking water from a private well, per USGS 2015 county water use. That is about 9% of residents.
Separately, the USGS national arsenic model estimates that 2% of the 16,175 people on private wells in Onslow County draw water above 10 ug/L (the model's range is 1% to 3%), from geology and well depth rather than local tests.
What homeowner tests found
NCWELL private well summaries: private wells tested and reported to the state, 1998 to 2019. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.
What individual samples found
Each row summarizes every public sample for that contaminant inside Onslow 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 1941 to 2024 | 97 | 49% | 0 | 664 | 10 mg/L EPA limit | |
| Fluoride 1941 to 2024 | 66 | 91% | 0.3 | 2.4 | 4 mg/L EPA limit | |
| Copper 1989 to 2024 | 34 | 26% | 0 | 0.01 | 1.3 mg/L EPA limit | |
| Lead 1989 to 2024 | 28 | 36% | 0 | 1.78 | 15 ug/L EPA limit | |
| Arsenic 2002 to 2024 | 20 | 45% | 0 | 0.4 | 10 ug/L EPA limit | |
| Uranium 2002 to 2024 | 20 | 20% | 0 | 0.152 | 30 ug/L EPA limit | |
| Radium (226 + 228) 2013 to 2021 | 13 | 62% | 0.07 | 1.6 | 5 pCi/L EPA limit | |
| Iron 1941 to 2024 | no limit | 67 | 99% | 442 | 9,280 | 300 ug/L nuisance level |
| Manganese 1948 to 2024 | no limit | 57 | 100% | 20 | 290 | 300 ug/L health guideline |
| Sodium 1941 to 2024 | no limit | 54 | 100% | 17 | 3,620 | 20 mg/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (7), PFOS (1), PFOA (1), Radon (8), Chloride (2).
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 | 19%47 samples | 9%22 samples | 0%14 samples | 0%14 samples |
| Fluoride | 0%36 samples | 0%16 samples | n/a | n/a |
Nitrate above the limit in Onslow County fell from 19% of 47 samples before 2000 to 9% of 22 in the 2000s.
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
Among homeowners in Onslow County who sent a sample to the state lab, the health-based limits most often exceeded were lead (3% of 234 wells) and arsenic (<1% of 234 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 Onslow County
- 1Nitrate11% of 97 local samples were above the limit.
- 2Lead3% of 234 local wells tested were above the North Carolina groundwater standard.
- 3Arsenic<1% of 234 local wells tested were above the North Carolina groundwater standard.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5Iron56% of 157 local wells tested were above the North Carolina groundwater standard.
- 6RadonMedian local reading is 143 pCi/L.
- 7Manganese26% of 234 local wells tested were above the North Carolina groundwater standard.
- 8ChlorideDetected in 100% of local samples.
- 9Volatile organic compounds (VOCs)836 leaking underground storage tank sites on record locally.
Test your Onslow County well for nitrate, lead 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 $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 North Carolina: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Onslow County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Onslow County
Castle Hayne aquifer
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 North Carolina
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 Testing FAQs, NCDHHS
- NCSLPH - Lab Certification, NCDHHS
Contamination sources on record in Onslow County
NC DEQ records 836 leaking underground storage tank sites in Onslow County, among 836 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.
- 836
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
Treatment that fits the local profile
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Manganese
Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
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 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.
Free, no obligation
Get on the list for a free in-home water test in Onslow County
No water treatment company serves Onslow 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 Onslow County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Onslow County?
Arsenic was detected in 45% of 20 public well samples in Onslow County, and 0% 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 Onslow 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 Onslow 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 North Carolina dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 475 samples in Onslow 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.
- NCWELL private well summaries: summaries for 7 contaminants in Onslow County, up to 234 wells each. County summaries of private well tests run by the NC State Laboratory of Public Health, 1998 to 2019, compiled by the UNC Superfund Research Program (NCWELL database). Counts are tests, not distinct wells; since 2008 every new well is tested once, so most tests are unique wells. Shares are against the NC 2L groundwater standard where one exists (manganese 50 ug/L, lead 15, iron 300) and otherwise the EPA limit. Medians are not used because more than half of results sit at the reporting limit for most analytes. Retrieved September 9, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 16,175 people on private wells in Onslow 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.
- NC DEQ regulated sites: 836 regulated sites located in Onslow County. Underground storage tank incidents from the North Carolina Department of Environmental Quality UST Section. Retrieved September 9, 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.