Well water in Delaware

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Testing strongly recommended

tested well samples in Delaware exceeded the EPA limit for PFOA (4 ng/L), based on public data from USGS Water Quality Portal.

13,133 test results across 15 contaminants from at least 936 wells, 1931 to 2026; nitrate has the most at 2,631. Data refreshed September 15, 2026.

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

An estimated 181,640 people in Delaware get their drinking water from a private well, per USGS 2015 county water use.

Separately, the USGS national arsenic model estimates that 5% of the 181,640 people on private wells in Delaware draw water above 10 ug/L (the model's range is 4% to 8%), from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Delaware. 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
PFOA 2018 to 2019	44%	34	50%	0.65	57	4 ng/L EPA limit
Nitrate 1931 to 2026	30%	2,631	81%	4.95	184	10 mg/L EPA limit
PFOS 2018 to 2019	24%	34	26%	0	59.0	4 ng/L EPA limit
Arsenic 1987 to 2025	5%	418	31%	0	27.3	10 ug/L EPA limit
Lead 1982 to 2026	3%	482	44%	0	1,420	15 ug/L EPA limit
Copper 1951 to 2026	<1%	468	44%	0	2.35	1.3 mg/L EPA limit
Fluoride 1943 to 2025	0%	1,140	47%	0	1.9	4 mg/L EPA limit
Uranium 2000 to 2024	0%	114	46%	0	0.747	30 ug/L EPA limit
Radium (226 + 228) 2000 to 2018	0%	113	58%	0.11	4.7	5 pCi/L EPA limit
E. coli 2001 to 2024	0%	25	0%	0	0	0 MPN/100mL EPA limit
Chloride 1931 to 2026	no limit	2,339	100%	18.2	70,300	250 mg/L nuisance level
Sodium 1931 to 2026	no limit	2,176	100%	11	5,500	20 mg/L health guideline
Iron 1931 to 2026	no limit	1,661	75%	25.6	430,000	300 ug/L nuisance level
Manganese 1951 to 2026	no limit	1,240	96%	23	54,000	300 ug/L health guideline
Radon 1988 to 2018	no limit	258	98%	250	2,600	2,000 pCi/L health guideline

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	28%1,286 samples	19%373 samples	42%725 samples	23%247 samples
Fluoride	0%641 samples	0%207 samples	0%271 samples	0%21 samples
Lead	1%270 samples	10%92 samples	0%47 samples	0%73 samples
Copper	<1%273 samples	0%74 samples	0%47 samples	0%74 samples
Arsenic	<1%205 samples	3%80 samples	18%84 samples	0%49 samples
Uranium	n/a	0%49 samples	0%47 samples	0%18 samples

Nitrate above the limit in Delaware fell from 42% of 725 samples in the 2010s to 23% of 247 in the 2020s.

Arsenic above the limit in Delaware fell from 18% of 84 samples in the 2010s to 0% of 49 in the 2020s.

Fluoride, lead, copper, uranium have held within a few points between the two most recent periods with enough samples.

What this means

The contaminants most often above their limit here are pfoa (44% of 34 samples), nitrate (30% of 2,631 samples), and pfos (24% of 34 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 Delaware

1
PFOA
44% of 34 local samples were above the limit.
2
Nitrate
30% of 2,631 local samples were above the limit.
3
PFOS
24% of 34 local samples were above the limit.
4
Arsenic
5% of 418 local samples were above the limit.
5
Lead
3% of 482 local samples were above the limit.
6
Copper
<1% of 468 local samples were above the limit.
7
Coliform bacteria
Recommended for every private well, every year.
8
Volatile organic compounds (VOCs)
4,518 leaking underground storage tank sites on record locally.

Test your Delaware well for PFOA, nitrate 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 Delaware: certified labs, state programs and prices.

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

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Send me the Delaware report

The numbers above, which tests to order and where, and the treatment that fits the local profile, in one email.

Wells in Delaware

89,231 domestic wells in Delaware are on record with the state since 1971. the typical well is 61 feet deep (one in ten goes past 190 feet).

In a typical Delaware well, the median yield is 35 gallons per minute, <1% of wells yield under 3 gallons per minute and usually need a storage tank.

5,302

1970s

16,700

1980s

18,818

1990s

16,672

2000s

10,871

2010s

8,065

2020s

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 Delaware

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 state 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 Delaware

DNREC leaking tank facilities records 4,518 leaking underground storage tank sites in Delaware, among 4,518 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.

4,518: 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

PFOA

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

Nitrate

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

PFOS

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

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

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 PFOA

Under-sink reverse osmosis system

under-sink or countertop, about $300

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

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 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 PFOS

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 PFOS

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.

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.

Common questions

How deep are wells in Delaware?

The typical domestic well in Delaware is 61 feet deep, based on 89,231 wells reported to the state since 1971. One in ten is deeper than 190 feet.

Is there arsenic in well water in Delaware?

Arsenic was detected in 31% of 418 public well samples in Delaware, and 5% 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 Delaware?

The median radon level across 258 public samples in Delaware was 250 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 Delaware?

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 in Delaware

Want the numbers themselves? Download the Delaware dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 13,133 samples in Delaware. 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 181,640 people on private wells in Delaware 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: 174,674 well records in Delaware, 89,231 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: 4,518 regulated sites located in Delaware. 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.