Thallium in drinking water
859 active public water systems in 43 states had a Thallium violation in the past three years, and 14 had one in the latest quarter of EPA's data.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Thallium and lists the water systems whose records include a related violation. It does not show measured levels.
Is Thallium 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
Thallium is a rare heavy metal that enters drinking water through leaching from ore-processing operations, discharge from electronics and pharmaceutical manufacturing, and natural mineral weathering. It is one of the least common contaminants detected in US public water systems but has a very low MCL due to its high toxicity.
Health effects
Chronic thallium exposure causes hair loss, changes in blood chemistry, kidney damage, intestinal problems, and liver effects. It can also impair the nervous system. EPA has classified thallium as a possible human carcinogen (Group C). The very low MCL reflects its acute toxicity even at small doses.
The standard and what a violation means
EPA limit: 0.002 mg/L (2 ppb).
Water systems with a Thallium 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 | In violation, latest quarter |
|---|---|---|---|
| Pennsylvania | 115 | 2% | 0 |
| Texas | 73 | 1% | 0 |
| Illinois | 69 | 1% | 2 |
| Georgia | 61 | 3% | 0 |
| New York | 55 | 1% | 0 |
| Michigan | 52 | 0% | 0 |
| Colorado | 29 | 1% | 4 |
| Indiana | 29 | 1% | 0 |
| West Virginia | 29 | 4% | 0 |
| New Jersey | 28 | 1% | 0 |
| California | 23 | 0% | 0 |
| Montana | 22 | 1% | 0 |
| Wyoming | 22 | 3% | 0 |
| Missouri | 21 | 1% | 2 |
| Washington | 21 | 0% | 0 |
| Oklahoma | 20 | 2% | 0 |
| Idaho | 19 | 1% | 1 |
| Connecticut | 17 | 1% | 0 |
| Virginia | 15 | 1% | 0 |
| Oregon | 13 | 1% | 0 |
| Maine | 12 | 1% | 0 |
| Utah | 11 | 1% | 0 |
| Wisconsin | 11 | 0% | 0 |
| Massachusetts | 10 | 1% | 2 |
| Nevada | 9 | 1% | 0 |
| Iowa | 8 | 0% | 0 |
| Alaska | 7 | 1% | 0 |
| Mississippi | 7 | 1% | 0 |
| Vermont | 7 | 1% | 2 |
| Arizona | 6 | 0% | 1 |
| North Carolina | 6 | 0% | 0 |
| Maryland | 5 | 0% | 0 |
| Minnesota | 5 | 0% | 0 |
| Alabama | 4 | 1% | 0 |
| Florida | 4 | 0% | 0 |
| Rhode Island | 3 | 1% | 0 |
| Kansas | 2 | 0% | 0 |
| New Hampshire | 2 | 0% | 0 |
| New Mexico | 2 | 0% | 0 |
| South Dakota | 2 | 0% | 0 |
| Hawaii | 1 | 1% | 0 |
| Kentucky | 1 | 0% | 0 |
| North Dakota | 1 | 0% | 0 |
Largest water systems with a Thallium 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 | |
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
Aqua WSC Bastrop County |
86,325 | 5 | 1 | |
|
GW Santa Cruz Water CO Maricopa · Pinal County |
84,000 | 7 | 0 | |
|
Tigard, City of Washington County |
62,500 | 2 | 0 | |
|
Greenlawn Water District Huntington (t) · Suffolk County |
42,000 | 3 | 0 | |
|
Winslow Twp Dmu Winslow Twp · Camden County |
39,174 | 6 | 0 | |
|
Jackson Twp Mua Jackson Twp · Ocean County |
37,224 | 3 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Thallium, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Thallium 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.