Arsenic in Drinking Water in Connecticut
What residents of Connecticut 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, Connecticut Department of Public Health, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Connecticut?
Yes. Connecticut has significant arsenic concerns due to its granite and crystalline bedrock geology. New England granites are naturally arsenic-bearing, and private wells drilled into bedrock throughout Connecticut can have elevated arsenic concentrations. Connecticut has one of the highest rates of arsenic occurrence in private well water of any state east of the Mississippi, and approximately 30% of Connecticut residents use private wells.
Where does arsenic come from in Connecticut's water?
Crystalline bedrock — primarily granite, schist, and gneiss — is the dominant source of arsenic in Connecticut groundwater. Private wells drilled into this bedrock are the primary exposure pathway. The arsenic leaches slowly from mineral crystals in the rock as groundwater flows through fractures and pores. The Hartford, Tolland, and Windham county areas with metamorphic and igneous bedrock have the highest documented occurrence.
What should Connecticut residents know?
Private well owners in Connecticut face significant arsenic risk from bedrock geology, regardless of their town or county. Connecticut DPH recommends testing private wells for arsenic. Standard water softeners and most pitcher filters do not remove arsenic. Reverse osmosis or certified activated alumina filters are required. Connecticut has a private well testing program available through the DPH.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Granite, schist, and gneiss bedrock — naturally arsenic-bearing New England crystalline geology |
| Private well exposure | ~30% of CT residents use private wells — high arsenic occurrence rate in bedrock wells |
| State recommendation | CT DPH recommends all private well owners test for arsenic |
| State regulator | Connecticut Department of Public Health |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes risk |
| Effective treatment | Reverse osmosis or certified activated alumina — standard pitcher filters do NOT remove arsenic |
Why Arsenic Matters in Connecticut
Connecticut's arsenic problem is fundamentally geological — New England's crystalline bedrock contains arsenic in mineral form that leaches into groundwater over time. Unlike contamination from a discrete industrial or military source, arsenic in Connecticut groundwater is ubiquitous and unpredictable: neighboring wells in similar geology can have very different arsenic concentrations. Connecticut DPH actively encourages private well testing and has provided guidance for homeowners. The state's significant private well population — roughly 400,000 households — means a substantial portion of the population may be exposed without knowing it.
Connecticut Arsenic Program
Connecticut DPH requires testing and has documented arsenic in private wells particularly in the western highlands on crystalline rock. Connecticut's bedrock geology includes arsenic-bearing sulfide minerals, and private well owners — especially in Fairfield and Litchfield counties — face elevated natural arsenic risk. Connecticut offers periodic state-sponsored well testing programs.
Connecticut Utilities With Arsenic Violation Records
The utilities listed below have at least one arsenic violation on record in EPA's SDWIS database. Violations may be open or resolved — see individual utility pages for current status and risk level.
Ctwc - Northern Reg-western System
East Granby,East Windsor,Ellington,Enfield,Manchester,Mansfield,South Windsor,Stafford,Suffield,Tolland,Vernon,Windsor Locks · 101,313 served
New Britain Water Department
Berlin,Farmington,New Britain,Newington,Plainville,West Hartford · 73,534 served
Southington Water Department
Connecticut · 43,069 served
Aquarion-new Milford Regional
Brookfield,New Milford · 13,331 served
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
Private well owners throughout Connecticut face arsenic risk from bedrock geology. Hartford County, Tolland County, Windham County, and New London County areas with metamorphic and igneous bedrock have the highest documented occurrence rates, but arsenic can occur in any county.
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 Connecticut
- 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 Connecticut Department 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 Connecticut, 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
Connecticut State Overview
All utilities and water quality data
Connecticut 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
Connecticut Department of Public Health ↗