Total Trihalomethanes (TTHM) in U.S. Drinking Water
Health-based violation data for Total Trihalomethanes (TTHM) from EPA Safe Drinking Water Information System (SDWIS). Covers all community water systems with violations on record.
Total Trihalomethanes (TTHM) has been found in violation of EPA standards in 3,233 water systems across 53 states, with 59,182 total health-based violations recorded. The most affected states are Oklahoma, Texas, Louisiana.
Total Trihalomethanes (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, SDWIS records show 59,182 health-based violations for Total Trihalomethanes (TTHM) affecting 3,233 community water systems in 53 states. Violation counts cluster heaviest in Oklahoma, Texas, Louisiana, with Oklahoma alone accounting for 13,837 violations 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 U.S. Environmental Protection Agency. Consult your doctor for personalized health guidance
Violations by State
States ranked by number of health-based violations for Total Trihalomethanes (TTHM).
| # | State | Violations | Systems Affected |
|---|---|---|---|
| 1 | Oklahoma | 13,837 | 294 |
| 2 | Texas | 10,418 | 468 |
| 3 | Louisiana | 7,109 | 174 |
| 4 | Arkansas | 2,338 | 95 |
| 5 | California | 2,016 | 120 |
| 6 | Florida | 1,292 | 116 |
| 7 | Missouri | 1,258 | 122 |
| 8 | New York | 1,181 | 119 |
| 9 | Kansas | 983 | 91 |
| 10 | Mississippi | 895 | 45 |
| 11 | North Carolina | 822 | 89 |
| 12 | Kentucky | 795 | 77 |
| 13 | Georgia | 749 | 50 |
| 14 | Ohio | 711 | 66 |
| 15 | Puerto Rico | 655 | 45 |
| 16 | Alaska | 630 | 35 |
| 17 | Pennsylvania | 597 | 62 |
| 18 | New Mexico | 580 | 19 |
| 19 | Illinois | 549 | 59 |
| 20 | Arizona | 542 | 31 |
| 21 | Virginia | 481 | 49 |
| 22 | West Virginia | 430 | 57 |
| 23 | Washington | 427 | 37 |
| 24 | Colorado | 377 | 34 |
| 25 | Tennessee | 376 | 37 |
| 26 | Indiana | 338 | 25 |
| 27 | South Carolina | 317 | 28 |
| 28 | Massachusetts | 259 | 30 |
| 29 | Maine | 254 | 16 |
| 30 | Montana | 241 | 15 |
| 31 | Oregon | 240 | 16 |
| 32 | Alabama | 209 | 27 |
| 33 | New Jersey | 141 | 25 |
| 34 | New Hampshire | 135 | 14 |
| 35 | Wyoming | 118 | 8 |
| 36 | Michigan | 115 | 20 |
| 37 | American Samoa | 96 | 1 |
| 38 | North Dakota | 77 | 12 |
| 39 | Rhode Island | 71 | 10 |
| 40 | Nebraska | 63 | 5 |
| 41 | Maryland | 62 | 13 |
| 42 | Nevada | 41 | 5 |
| 43 | Utah | 40 | 6 |
| 44 | Connecticut | 36 | 6 |
| 45 | Wisconsin | 33 | 8 |
| 46 | Iowa | 27 | 11 |
| 47 | Idaho | 23 | 4 |
| 48 | South Dakota | 21 | 7 |
| 49 | Minnesota | 17 | 6 |
| 50 | Delaware | 6 | 2 |
| 51 | Vermont | 5 | 2 |
| 52 | District of Columbia | 2 | 1 |
| 53 | Hawaii | 1 | 1 |
Most Affected Water Systems
Top 50 water systems by number of Total Trihalomethanes (TTHM) health-based violations.
Frequently Asked Questions
Is Total Trihalomethanes (TTHM) in my water?
Total Trihalomethanes (TTHM) has been detected in violation of EPA health standards in 3,233 water systems across 53 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 Total Trihalomethanes (TTHM) violations?
EPA SDWIS records show 3,233 community water systems with health-based Total Trihalomethanes (TTHM) violations, totaling 59,182 violations. These represent cases where the contaminant exceeded the EPA Maximum Contaminant Level (MCL).
Which states have the most Total Trihalomethanes (TTHM) violations?
The states with the most Total Trihalomethanes (TTHM) violations are: Oklahoma (13,837 violations), Texas (10,418 violations), Louisiana (7,109 violations), Arkansas (2,338 violations), California (2,016 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 U.S. Environmental Protection Agency, SDWIS Federal Reporting Services
Read our methodology - how this data is sourced, computed, and verified.