Manganese and arsenic are widespread in New Castle County wells.
2 widespread, 1 worth checking, 2 rare out of 5 health checks.
From 100 wells tested in New Castle County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: uranium (6), lead (5).
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
1 in 12 people 47,474 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Deep wells: fewer surface germs, more minerals from the rock.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Possible here. A home air test is inexpensive.
Radon zones: EPA map
Here's how New Castle County compares with Delaware and the counties around it.
Each result puts New Castle County next to the 7 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in New Castle County wells.
Manganese20 of 84 wells over
Too few tested to show: Delaware, PA.
Arsenic6 of 30 wells over
Too few tested to show: Delaware, PA.
This one is worth checking in New Castle County.
Nitrate7 of 100 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Delaware, PA.
These 2 are rare in New Castle County.
Radon in water0 of 32 wells over
Too few tested to show: Cecil, MD, Delaware, PA, Kent, MD, Salem, NJ.
Fluoride0 of 84 wells over
Too few tested to show: Delaware, PA.
Too few New Castle County wells were tested for these 2.
Uranium6 wells tested
Lead5 wells tested
Coliform bacteria turned up in 2 of 2 tested New Castle County wells, so test for it every year.
Coliform bacteria2 of 2 wells had it
E. coli1 of 2 wells had it
E. coli means human or animal waste is getting in, so if a test of your New Castle County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 46 of 100 tested wells, and it isn't a health risk.
Iron stains46 of 100 wells had it
Too few tested to show: Delaware, PA.
New Castle County has 100 tested wells, and the busiest decade for testing was the 2010s.
Only 18 of the 100 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most New Castle County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 4 things to check in New Castle County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Delaware offers well owners
- Free testingDPH offers free test kits for bacteria and ten chemical parameters, and DNREC and DHSS offer free sampling for PFAS and other contaminants to private well users. See the program
- Certified labsDelaware's list of certified labs
- Well recordsDelaware's well record search
Half the household wells here are shallower than 160 feet.
That comes from 1,313 household wells in Delaware's drilling records. Most wells of every kind here are 20 to 170 feet deep. Wells as deep as New Castle County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium.
Look up your own well's depth in Delaware's well record search, or see how to find it.
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in New Castle County.
New Castle County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide
Between 2023 and 2025 the EPA had 8 town water systems in New Castle County test for PFAS. 4 of them had at least one test above 4 ng/L, the new EPA limit for PFOA and PFOS. The highest single result was 25 ng/L of PFOA. Only 3 wells in New Castle County have public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in New Castle County
Is well water in New Castle County safe to drink?
20 of 84 wells tested in New Castle County had manganese over the limit, about 1 in 4. Across Delaware it's about 1 in 11. So test your own well for manganese before you count on it.
Can I get my well tested for free in New Castle County?
DPH offers free test kits for bacteria and ten chemical parameters, and DNREC and DHSS offer free sampling for PFAS and other contaminants to private well users. If not, use a lab Delaware has certified for drinking water. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in New Castle County.
How deep are wells in New Castle County?
Half the household wells here are shallower than 160 feet.
How does New Castle County compare with the counties around it?
For manganese, the share of tested wells over the limit: 1 of the 6 neighboring counties with data had a higher share than New Castle County, at 24%. Cecil, MD had the most, at 56%. Groundwater doesn't stop at county lines, so Cecil, MD's 56% is worth knowing about if you live near it.
How often should I test my well in New Castle County?
In New Castle County, 2 of 2 tested wells had coliform bacteria, so the CDC's advice matters here: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the New Castle County numbers come from
- People on wells: 47,474 in New Castle County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 618 well water samples from 100 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2025.
- Well depths: 1,313 Delaware drilling records for New Castle County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 7 counties that share a border with New Castle County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 8 town water systems in New Castle County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: New Castle County is zone 2 on the EPA Map of Radon Zones.
- State programs and links: Department of Health and Social Services, Division of Public Health (with DNREC), checked November 1, 2026.