Arsenic in Drinking Water in Maryland
What residents of Maryland 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, Maryland Department of the Environment, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Maryland?
Yes. Maryland has arsenic concerns primarily in the Piedmont region of central Maryland — Baltimore, Carroll, Howard, Frederick, and Montgomery counties — where crystalline bedrock geology similar to the broader New England/Mid-Atlantic Piedmont creates conditions for naturally occurring arsenic in private well water. Maryland also has some arsenic occurrence in the Eastern Shore's Coastal Plain aquifer systems.
Where does arsenic come from in Maryland's water?
Crystalline Piedmont bedrock — granite, gneiss, and schist — is the primary arsenic source in central Maryland. Private wells drilled into this bedrock in Baltimore, Carroll, Howard, Frederick, and Montgomery counties face the most direct risk. The Eastern Shore's Coastal Plain aquifer systems have secondary arsenic occurrence under reducing geochemical conditions.
What should Maryland residents know?
Private well owners in Maryland's Piedmont counties should test for arsenic. Maryland MDE monitors public water systems, but approximately 15% of Maryland residents use private wells, primarily in rural and suburban Piedmont areas. Maryland requires arsenic testing at real estate transfer for properties with private wells — an important consumer protection.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Piedmont crystalline bedrock (Baltimore/Carroll/Frederick/Howard counties); Coastal Plain aquifers (Eastern Shore) |
| State requirement | Maryland requires arsenic testing at real estate transfer for private well properties |
| State regulator | Maryland Department of the Environment (MDE) |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes risk |
| Effective treatment | Reverse osmosis (NSF/ANSI 58) or activated alumina |
Why Arsenic Matters in Maryland
Maryland's Piedmont geology — shared with neighboring Virginia, Pennsylvania, and Delaware — creates conditions for arsenic occurrence in private well water across a band of central Maryland from the Pennsylvania border south toward the Washington, D.C. suburbs. The high residential density of suburban Maryland counties like Howard, Montgomery, and Frederick means a significant number of suburban private well users may face arsenic exposure. Maryland MDE's real estate transfer testing requirement helps identify affected wells, but owners in existing homes without recent testing may be unaware of their arsenic levels.
Maryland Arsenic Program
Maryland MDE monitors arsenic under federal SDWIS and has documented elevated arsenic in private wells in the Piedmont and western Maryland counties on crystalline and sedimentary rock. Arsenic is an ongoing concern for private well owners in Carroll, Frederick, Washington, and Garrett counties. MDE recommends arsenic testing for all new wells and periodic retesting.
Maryland 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.
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 in Carroll, Frederick, Howard, Baltimore, and western Montgomery counties in Maryland's Piedmont, and Eastern Shore private well users in Dorchester, Wicomico, Somerset, and Worcester counties with Coastal Plain aquifer dependency, face the most relevant arsenic risk.
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 Maryland
- 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 Maryland Department of the Environment-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 Maryland, 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
Maryland State Overview
All utilities and water quality data
Maryland 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
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Maryland Department of the Environment ↗