Arsenic in drinking water
1,798 active public water systems in 47 states had a Arsenic violation in the past three years, and 234 have one that is still unresolved.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Arsenic and lists the water systems whose records include a related violation. It does not show measured levels.
Is Arsenic in the records for your water system?
Enter a ZIP code, town, or street address to see the water systems that serve your area, their status, and which rules and contaminants appear in their violations.
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What it is and where it comes from
Arsenic is a naturally occurring metalloid found in bedrock and soil. It dissolves into groundwater from natural deposits and can also come from mining, smelting and past pesticide use. EPA lowered the MCL from 50 ppb to 10 ppb in 2001.
Health effects
Long-term arsenic exposure increases risk of bladder, lung, and skin cancers. It is also associated with cardiovascular disease, type 2 diabetes, and developmental effects in children. Arsenic is classified as a Group A human carcinogen by the EPA.
The standard and what a violation means
EPA limit: 0.010 mg/L (10 ppb), set in 2001 and enforceable since 2006; the previous MCL was 0.050 mg/L (50 ppb).
Water systems with a Arsenic violation, by state
Active public water systems that reported at least one related violation to EPA in the past three years. Each state links to the list of its affected systems.
| State | Systems with violations, 3 yr | Share of active systems | Unresolved |
|---|---|---|---|
| Michigan | 186 | 2% | 30 |
| Pennsylvania | 166 | 2% | 5 |
| Texas | 154 | 2% | 41 |
| California | 114 | 2% | 24 |
| Arizona | 105 | 6% | 26 |
| Illinois | 95 | 2% | 6 |
| Washington | 78 | 2% | 10 |
| New York | 74 | 1% | 0 |
| Georgia | 67 | 3% | 4 |
| Indiana | 57 | 1% | 7 |
| Oregon | 56 | 2% | 11 |
| Nevada | 41 | 7% | 6 |
| Oklahoma | 40 | 3% | 0 |
| New Jersey | 39 | 1% | 0 |
| Colorado | 36 | 2% | 7 |
| Idaho | 35 | 2% | 11 |
| New Hampshire | 35 | 1% | 0 |
| Montana | 33 | 1% | 0 |
| Maine | 31 | 2% | 3 |
| Utah | 27 | 3% | 4 |
| Alaska | 26 | 2% | 5 |
| West Virginia | 26 | 3% | 1 |
| Connecticut | 25 | 1% | 2 |
| Wyoming | 24 | 3% | 0 |
| Minnesota | 23 | 0% | 7 |
| Ohio | 23 | 1% | 5 |
| Missouri | 21 | 1% | 2 |
| Wisconsin | 20 | 0% | 2 |
| Maryland | 17 | 1% | 1 |
| New Mexico | 17 | 1% | 3 |
| Massachusetts | 16 | 1% | 2 |
| Iowa | 15 | 1% | 1 |
| Virginia | 15 | 1% | 0 |
| Vermont | 14 | 1% | 3 |
| Mississippi | 8 | 1% | 0 |
| North Carolina | 7 | 0% | 1 |
| Nebraska | 6 | 0% | 1 |
| Florida | 5 | 0% | 0 |
| Alabama | 4 | 1% | 0 |
| Louisiana | 4 | 0% | 3 |
| Rhode Island | 3 | 1% | 0 |
| South Dakota | 3 | 0% | 0 |
| Kansas | 2 | 0% | 0 |
| North Dakota | 2 | 1% | 0 |
| Hawaii | 1 | 1% | 0 |
| Kentucky | 1 | 0% | 0 |
| Tennessee | 1 | 0% | 0 |
Largest water systems with a Arsenic violation
The ten biggest systems, by people served, whose records include a related violation in the past three years.
| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Aqua PA Main System Montgomery County |
822,600 | 6 | 0 | |
|
Aquarion-Eastern Fairfield County Beacon Falls, Bridgeport, Darien and 17 more · Fairfield County |
351,756 | 2 | 0 | |
|
Gilbert, Town of Gilbert · Maricopa County |
247,600 | 9 | 1 | |
|
Chandler City of Chandler · Maricopa County |
247,328 | 4 | 0 | |
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
City of Midland Water Purification Plant Midland County |
157,000 | 3 | 1 | |
|
Arizona Water CO Pinal Valley Casa Grande · Pinal County |
134,432 | 2 | 0 | |
|
Epcor Agua Fria Surprise · Maricopa County |
128,040 | 5 | 0 | |
|
ST George City Water System Washington County |
105,240 | 1 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Arsenic, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Arsenic alone. Counts cover active systems in all 50 states and the District of Columbia.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.