TTHM in U.S. Drinking Water
Health-based violation data for TTHM from EPA Safe Drinking Water Information System (SDWIS). Covers all community water systems with violations on record.
TTHM has been found in violation of EPA standards in 3,265 water systems across 54 states, with 61,938 total health-based violations recorded. The most affected states are Oklahoma, Texas, Louisiana.
TTHM is regulated under the EPA Safe Drinking Water Act, which sets enforceable Maximum Contaminant Levels (MCLs) and associated treatment technique requirements for public water systems. The EPA Safe Drinking Water Information System (SDWIS) tracks every recorded violation nationwide and links it back to the specific public water system (PWSID), violation type, and begin date.
Across the United States, PlainEnviro's joined extract contains 61,938 health-based violation records carrying TTHM (EPA code 2950) across 3,265 active community water systems in 54 states. Raw record counts are highest in Oklahoma, Texas, Louisiana, with Oklahoma accounting for 14,300 records across 294 systems. EPA health-effect summaries describe the specific exposure concerns that drove the federal standard.
A health-based violation does not mean residents were necessarily harmed, it means the contaminant exceeded the federal MCL in a compliance sample, triggering notification and remediation requirements. States and utilities maintain primary enforcement responsibility. To check the status of a specific water system, request its most recent Consumer Confidence Report or consult the EPA's Drinking Water Watch portal for the corresponding state.
What are the health effects of this contaminant?
Trihalomethanes form when chlorine used to disinfect water reacts with organic matter. Long-term exposure above EPA limits is linked to increased risk of bladder cancer and adverse reproductive outcomes.
Source: U.S. Environmental Protection Agency. Consult your doctor for personalized health guidance
Violations by State
States ranked by number of health-based violations for TTHM.
| # | State | Violations | Systems Affected |
|---|---|---|---|
| 1 | Oklahoma | 14,300 | 294 |
| 2 | Texas | 11,255 | 477 |
| 3 | Louisiana | 7,559 | 173 |
| 4 | Arkansas | 2,415 | 99 |
| 5 | California | 2,031 | 121 |
| 6 | Missouri | 1,342 | 125 |
| 7 | Florida | 1,311 | 116 |
| 8 | New York | 1,200 | 124 |
| 9 | Kansas | 998 | 91 |
| 10 | Mississippi | 937 | 45 |
| 11 | North Carolina | 888 | 90 |
| 12 | Kentucky | 844 | 77 |
| 13 | Georgia | 789 | 50 |
| 14 | Ohio | 746 | 67 |
| 15 | New Mexico | 659 | 18 |
| 16 | Puerto Rico | 655 | 45 |
| 17 | Alaska | 642 | 36 |
| 18 | Pennsylvania | 567 | 63 |
| 19 | Illinois | 566 | 60 |
| 20 | Arizona | 549 | 31 |
| 21 | Virginia | 501 | 50 |
| 22 | Washington | 471 | 38 |
| 23 | West Virginia | 448 | 57 |
| 24 | Tennessee | 414 | 38 |
| 25 | Colorado | 381 | 34 |
| 26 | Indiana | 345 | 25 |
| 27 | South Carolina | 345 | 29 |
| 28 | Montana | 307 | 15 |
| 29 | Massachusetts | 272 | 30 |
| 30 | Maine | 261 | 16 |
| 31 | Oregon | 249 | 16 |
| 32 | Alabama | 234 | 28 |
| 33 | New Jersey | 153 | 25 |
| 34 | New Hampshire | 143 | 14 |
| 35 | Wyoming | 128 | 8 |
| 36 | Michigan | 126 | 20 |
| 37 | American Samoa | 96 | 1 |
| 38 | North Dakota | 90 | 12 |
| 39 | Rhode Island | 75 | 10 |
| 40 | Maryland | 65 | 13 |
| 41 | Nebraska | 64 | 5 |
| 42 | Nevada | 42 | 5 |
| 43 | Utah | 40 | 6 |
| 44 | Connecticut | 37 | 6 |
| 45 | Wisconsin | 33 | 8 |
| 46 | Iowa | 27 | 11 |
| 47 | Idaho | 26 | 4 |
| 48 | South Dakota | 23 | 7 |
| 49 | Minnesota | 21 | 6 |
| 50 | Delaware | 7 | 2 |
| 51 | Vermont | 5 | 2 |
| 52 | District of Columbia | 4 | 1 |
| 53 | Guam | 3 | 1 |
| 54 | Hawaii | 1 | 1 |
Most Affected Water Systems
Top 50 water systems by number of TTHM health-based violations.
Frequently Asked Questions
Is TTHM in my water?
TTHM has been detected in violation of EPA health standards in 3,265 water systems across 54 states. To check your specific utility, look up your annual Consumer Confidence Report (CCR) - water systems are required to disclose all violations.
How many water systems have TTHM violations?
EPA SDWIS records show 3,265 community water systems with health-based TTHM violations, totaling 61,938 violations. These represent cases where the contaminant exceeded the EPA Maximum Contaminant Level (MCL).
Which states have the most TTHM violations?
The states with the most TTHM violations are: Oklahoma (14,300 violations), Texas (11,255 violations), Louisiana (7,559 violations), Arkansas (2,415 violations), California (2,031 violations).
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About This Data
Violation data is from the EPA Safe Drinking Water Information System (SDWIS). Only health-based violations are shown, these include Maximum Contaminant Level (MCL) and Treatment Technique (TT) violations. Monitoring and reporting violations are excluded. Data may not reflect the most current enforcement actions.
Source: U.S. Environmental Protection Agency, SDWIS Federal Reporting Services
Read our methodology - how this data is sourced, computed, and verified.