Well water in New Castle County, Delaware
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Testing recommended
tested well samples in New Castle County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
4,360 test results across 15 contaminants from at least 334 wells, 1951 to 2026; chloride has the most at 883. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 56,989 people in New Castle County get their drinking water from a private well, per USGS 2015 county water use. That is about 10% of residents.
Separately, the USGS national arsenic model estimates that 3% of the 56,989 people on private wells in New Castle County draw water above 10 ug/L (the model's range is 2% 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 New Castle 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 1951 to 2025 | 824 | 70% | 2.79 | 138 | 10 mg/L EPA limit | |
| Arsenic 1987 to 2024 | 140 | 26% | 0 | 26.8 | 10 ug/L EPA limit | |
| Lead 1987 to 2024 | 143 | 19% | 0 | 20 | 15 ug/L EPA limit | |
| Fluoride 1951 to 2024 | 377 | 59% | 0.1 | 1.14 | 4 mg/L EPA limit | |
| Copper 1951 to 2024 | 146 | 25% | 0 | 0.148 | 1.3 mg/L EPA limit | |
| Radium (226 + 228) 2000 to 2018 | 37 | 57% | 0.05 | 4.7 | 5 pCi/L EPA limit | |
| Uranium 2001 to 2024 | 17 | 76% | 0.049 | 0.747 | 30 ug/L EPA limit | |
| Chloride 1951 to 2026 | no limit | 883 | 100% | 26 | 70,300 | 250 mg/L nuisance level |
| Sodium 1951 to 2026 | no limit | 854 | 100% | 18 | 859 | 20 mg/L health guideline |
| Iron 1951 to 2025 | no limit | 405 | 88% | 110 | 430,000 | 300 ug/L nuisance level |
| Manganese 1951 to 2024 | no limit | 356 | 96% | 29.5 | 54,000 | 300 ug/L health guideline |
| Radon 1988 to 2018 | no limit | 165 | 98% | 290 | 2,600 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOA (4), PFOS (4), E. coli (5).
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 | 16%581 samples | 15%99 samples | 15%124 samples | 20%20 samples |
| Fluoride | 0%255 samples | 0%57 samples | 0%62 samples | n/a |
| Arsenic | 0%98 samples | n/a | 20%30 samples | n/a |
| Radium (226 + 228) | n/a | 0%21 samples | 0%16 samples | n/a |
Nitrate above the limit in New Castle County rose from 15% of 124 samples in the 2010s to 20% of 20 in the 2020s.
Arsenic above the limit in New Castle County rose from 0% of 98 samples before 2000 to 20% of 30 in the 2010s.
Fluoride 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 addressWhat this means
The contaminants most often above their limit here are nitrate (16% of 824 samples), arsenic (4% of 140 samples), and lead (<1% of 143 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 New Castle County
- 1Nitrate16% of 824 local samples were above the limit.
- 2Arsenic4% of 140 local samples were above the limit.
- 3Lead<1% of 143 local samples were above the limit.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5RadonMedian local reading is 290 pCi/L.
- 6PFOAAbove the limit in 4 of 4 local samples; too few to quote a rate.
- 7PFOSAbove the limit in 2 of 4 local samples; too few to quote a rate.
- 8Volatile organic compounds (VOCs)2,680 leaking underground storage tank sites on record locally.
Test your New Castle County well for nitrate, arsenic and lead
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 Delaware: certified labs, state programs and prices.
Already have results back? Get your lab report read against the New Castle County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in New Castle County
8,755 domestic wells in New Castle County are on record with the state since 1971. the typical well is 135 feet deep (one in ten goes past 300 feet).
In a typical New Castle County well, the median yield is 20 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 DNREC well permits and choose Water Well.
- The report lists depth, screen, static water level and the pump test.
Delaware has permitted every well since 1966.
The rock under New Castle County
Northern Atlantic Coastal Plain aquifer system
Semiconsolidated sand. Coastal plain sands like these give steady yields at moderate depth. Salt water and sodium are the usual issues near the coast, and nitrate where the water table is shallow; arsenic and radon from bedrock are less common.
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 Delaware
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, Delaware DPH
Contamination sources on record in New Castle County
DNREC leaking tank facilities records 2,680 leaking underground storage tank sites in New Castle County, among 2,680 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.
- 2,680
- 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
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Lead
Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
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
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 lead
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 lead
Acid neutralizing filter
whole-house, at the point of entry, about $1,200
Raises pH so plumbing stops leaching lead and copper.
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 New Castle County
No water treatment company serves New Castle 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 New Castle County, and you get an email naming it first.
Common questions
How deep are wells in New Castle County?
The typical domestic well in New Castle County is 135 feet deep, based on 8,755 wells reported to the state since 1971. One in ten is deeper than 300 feet.
Is there arsenic in well water in New Castle County?
Arsenic was detected in 26% of 140 public well samples in New Castle County, and 4% 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 New Castle County?
The median radon level across 165 public samples in New Castle County was 290 pCi/L, with a high of 2,600 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in New Castle 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 New Castle 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 Delaware dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 4,360 samples in New Castle 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 56,989 people on private wells in New Castle 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.
- Delaware DNREC non-public well permits: 31,944 well records in New Castle County, 8,755 domestic. Non-public well permits and completion reports from the Delaware Department of Natural Resources and Environmental Control. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 18, 2026.
- DNREC leaking tank facilities: 2,680 regulated sites located in New Castle County. Leaking underground storage tank facilities from the Delaware Department of Natural Resources and Environmental Control. Retrieved September 18, 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.