What TTHM is, and why it's regulated
What the EPA limit means
80 µg/L
Maximum Contaminant Level — the enforceable ceiling a supplier must stay under.
—
Health goal (MCLG) — the level with no known health effect. It is a goal, not a legal limit, and is often zero for carcinogens.
SYR4
Where these measurements come from. Hover the tag for the EPA programme and years.
Where TTHM was found
The water suppliers reporting the highest levels, worst first. For lead and copper that is the 90th-percentile result the action level is written against; for Six-Year Review data, the 95th percentile of each system's samples.
| Supplier | City | State | Level vs EPA limit |
|---|---|---|---|
| Dry Town | Hayward | WI | 2661.5 µg/L 3327% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Choconut Creek Apartments | — | NY | 1275.53 µg/L 1594% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Colchester Estates | Colchester | NY | 769.065 µg/L 961% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Lakeshore Sites Water | Haskell | TX | 720.4 µg/L 900% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Rowena Wsc | Rowena | TX | 548.6 µg/L 686% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Coke County Wsc | — | TX | 504.7 µg/L 631% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| East Columbia Water System | Columbia | LA | 496.605 µg/L 621% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Pleasant Hills-Crossroads Water Systems | Joyce | LA | 495.36 µg/L 619% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| City of Nome | — | TX | 493.2 µg/L 617% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Village of Calvin Water System | Calvin | LA | 482.22 µg/L 603% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Chefornak Water System | Chefornak | AK | 454.62 µg/L 568% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Wildwood Mhp Ws | West Monroe | LA | 449.38 µg/L 562% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Hudson Gaars Mill Water System | Dodson | LA | 446.325 µg/L 558% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Walnut Ridge Estates Water System | Huntington | TX | 438 µg/L 548% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Ramsey Water System | West Monroe | LA | 434.76 µg/L 543% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Lincoln Hills Subdivision Ws | West Monroe | LA | 429.85 µg/L 537% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Hidden Oaks Subdivision Ws | West Monroe | LA | 425.7 µg/L 532% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Better Waterworks Water System | West Monroe | LA | 423.62 µg/L 530% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Beverly Beach Water System | Beverly Beach | FL | 420.291 µg/L 525% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Choctaw Co. Rwsg & Swmd #6 | Boswell | OK | 416.565 µg/L 521% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Beechwood Wsc | Hemphill | TX | 413.25 µg/L 517% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| The Trails S/D | Chapel Hill | NC | 396.35 µg/L 495% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Sandy Point 480 Water System | Campti | LA | 392.55 µg/L 491% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Boswell Public Works Authority | Boswell | OK | 388.495 µg/L 486% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
| Wenden Dwid | Wenden | AZ | 387.15 µg/L 484% of the EPA limit, at the 95th percentile of samples — 80 µg/L |
Frequently asked questions about TTHM
What is TTHM in drinking water?
Total trihalomethanes are by-products formed when chlorine reacts with organic matter; long-term exposure is linked to bladder cancer.
What is the EPA limit for TTHM?
The EPA's Maximum Contaminant Level for TTHM is 80 µg/L. A result above the limit means the supplier must act; the goal is the level at which no health effects are expected.
How common is TTHM in US tap water?
Of the 35,559 water suppliers with results on file, 30,898 detected TTHM — 86.9% of those tested.