Arsenic in Drinking Water in Delaware
What residents of Delaware need to know about arsenic in drinking water — including natural geological sources, private well risk, which utilities have documented violations, and how to remove arsenic from tap water.
Source: EPA SDWIS, Delaware Division of Public Health, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Delaware?
Arsenic is a moderate concern in Delaware, primarily for private well users in areas with coastal plain sedimentary geology in Sussex County and parts of Kent County. Delaware's Coastal Plain sediments — which underlie most of the state — can contain naturally occurring arsenic in reducing geochemical conditions at depth. Agricultural activities and poultry industry waste management have also historically raised concerns about arsenic loading in some rural areas.
Where does arsenic come from in Delaware's water?
Naturally occurring arsenic in Coastal Plain sedimentary aquifers is the primary pathway in Delaware. Deep groundwater wells in Sussex and Kent counties drawing from confined aquifer units can encounter reducing conditions where arsenic mobilizes from sediments. Agricultural use of arsenic-containing poultry litter historically used as fertilizer has also been documented as a secondary pathway in some areas of Sussex County.
What should Delaware residents know?
Private well owners in rural Sussex County and parts of Kent County should test their wells for arsenic. Delaware DPH monitors public water systems but private wells are unregulated. Sussex County's reliance on groundwater and its agricultural character — particularly poultry farming — make arsenic a relevant concern for rural residents.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Coastal Plain sedimentary aquifer geology (reducing conditions at depth) in Sussex and Kent counties |
| Secondary concern | Historical use of arsenic-containing compounds in poultry farming in Sussex County |
| State regulator | Delaware Division of Public Health |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes |
| Effective treatment | Reverse osmosis (NSF/ANSI 58) or activated alumina |
Why Arsenic Matters in Delaware
Delaware's Coastal Plain geology creates conditions for arsenic occurrence in deeper groundwater. Sussex County — Delaware's southernmost and most rural county — relies heavily on groundwater from Coastal Plain aquifers, and some wells have documented arsenic above the MCL. The county's agricultural character, with extensive poultry operations historically using arsenic compounds in feed additives, has added to arsenic loading concerns in soil and shallow groundwater. Delaware DPH has worked with affected communities and monitors public system compliance.
Delaware Arsenic Program
Delaware DPH monitors arsenic under federal SDWIS. Arsenic is not a primary natural concern in Delaware's Coastal Plain geology, but localized industrial contamination from legacy chemical manufacturing in New Castle County may contribute arsenic to some groundwater. Private well owners in northern Delaware near industrial sites should test.
Largest Delaware Water Utilities
No arsenic violations on record in EPA SDWIS for Delaware utilities in our database. Browse the largest utilities to review their full water quality record.
How Does Arsenic Get Into Drinking Water?
Arsenic in drinking water is almost always naturally occurring — it leaches from arsenic-bearing rocks and minerals into groundwater over time. New England granite, Southwest volcanic geology, and Upper Midwest glacial aquifers are the primary high-risk formations. It has no taste, odor, or color.
Full arsenic overview — geology maps, health effects, all 50 statesWho Should Pay Closest Attention
Rural Sussex County private well users, communities in Kent County relying on deeper Coastal Plain aquifer systems, and agricultural areas where poultry farming has historically been intensive face the most relevant arsenic concerns.
Private well owners near mining districts or agricultural areas
Residents in states with documented volcanic or geothermal geology
Long-term consumers of water from small groundwater systems
Households in homes built before 1960 with older well casings
Residents whose well water has never been tested for arsenic
Anyone living in a state where bedrock wells are common
How to Check Your Situation in Delaware
- 1
Identify your water source. If you use a public utility, use the ZIP lookup on this page to find your system and check its compliance record.
- 2
If on public water, review your utility's most recent Consumer Confidence Report (CCR) for arsenic monitoring data. The MCL is 10 ppb — your report should show recent test results.
- 3
If on a private well, order an arsenic test from a Delaware Division of Public Health-certified laboratory. A basic arsenic test costs $15–$40. The state agency website maintains a certified lab list.
- 4
Test your well at the tap — not just at the wellhead. The entire water distribution system within your home can affect water quality.
- 5
If your test shows arsenic above 5 ppb, install certified treatment immediately. If above 10 ppb, do not use the water for drinking or cooking until treatment is installed.
- 6
Retest after installing treatment to confirm it is working as certified. Replace filter media on the manufacturer's schedule — an exhausted filter may not perform as rated.
Treatment Options for Arsenic
Boiling does not remove arsenic — it concentrates it. Standard activated carbon filters (Brita, etc.) do not effectively remove arsenic. Certified treatment is required.
NSF/ANSI Standard 58 — Reverse Osmosis
RO systems certified to NSF/ANSI 58 remove 85–95% of arsenic. Under-sink installation. Most effective for removing multiple contaminants simultaneously. Replace membranes and pre-filters on schedule.
Activated Alumina Filters
Activated alumina is specifically designed for arsenic and fluoride removal. Point-of-use or whole-house options available. Must be certified by NSF International or WQA for arsenic reduction. Requires periodic media regeneration or replacement.
Iron/Manganese Oxidation Filters
Effective for arsenic in iron-rich well water, which is common in the Midwest and New England. Oxidation converts dissolved iron and arsenic to a form that can be filtered out. Best when arsenic is co-occurring with high iron levels.
What does NOT work for arsenic
Standard activated carbon filters (Brita, refrigerator filters, most pitcher filters) do NOT effectively remove arsenic. Boiling concentrates arsenic. Water softeners do not remove arsenic. Only use products with NSF certification specifically for arsenic reduction.
Take Action Now
If you use a private well in Delaware, test for arsenic — especially if you are in a region with granite, volcanic, or sedimentary geology. A basic arsenic test costs $15–$40 at a state-certified lab.
Public water users: check your utility's Consumer Confidence Report (CCR) for arsenic results. The EPA MCL is 10 ppb — any detection warrants attention.
If arsenic is detected above 10 ppb (or even below it, given MCLG is zero), install an NSF/ANSI 58-certified reverse osmosis system for drinking and cooking water.
Standard carbon filters do NOT remove arsenic — do not rely on a Brita or refrigerator filter for arsenic protection.
Frequently Asked Questions
Related Pages
Arsenic — National Overview
All U.S. utilities with arsenic records
Delaware State Overview
All utilities and water quality data
Delaware Well Water Guide
Testing, risks & certified labs for private wells
Reverse Osmosis Guide
Removes 85–95% of arsenic
Best Arsenic Filter Guide
What actually works (carbon doesn't)
PFAS in Drinking Water
The 'forever chemical' contamination overview
All Contaminants
Complete reference library
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Find Your Utility
State Regulator
Delaware Division of Public Health ↗