Private wells
Delaware well water: who's on a well and what to test for
People on private wells
235,500
Homes on wells
23.5%
Est. above arsenic limit
9,900
Every Delaware county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| Sussex County | 116,400 | 41% | 2.1% | 4.1 | 70 ft |
| Kent County | 71,700 | 40% | 1.8% | 4.9 | 50 ft |
| New Castle County | 47,500 | 8% | 2.1% | 1.2 | 160 ft |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Most well users above the arsenic limit
- Sussex County: about 4,800 people
- Kent County: about 3,600 people
- New Castle County: about 1,500 people
Highest modeled nitrate
- Kent County: 4.9 mg/L average (limit 10)
- Sussex County: 4.1 mg/L average (limit 10)
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Questions
Which Delaware counties rely most on wells?+
By share of homes: Sussex County (41%), Kent County (40%), New Castle County (8%). By number of people: Sussex County (116,400), Kent County (71,700), New Castle County (47,500).
Is arsenic a problem in Delaware wells?+
USGS estimates about 9,900 Delaware well users have water above the 10 microgram per liter arsenic limit that applies to public systems, the largest numbers in Sussex County, Kent County, New Castle County. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Delaware?+
We could not confirm a statewide rule for Delaware. Check with your county health department. Buyers can still make a lab test a condition of the offer.
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).