Total trihalomethanes (TTHM) in drinking water
Also called TTHMs, trihalomethanes.
Formed when chlorine reacts with natural organic matter. The limit is a running annual average.
Health: Long-term exposure linked to bladder cancer and liver and kidney effects.
Across the US
2,641 community water systems had at least one health-based Total trihalomethanes (TTHM) violation since 2016. Routine Total trihalomethanes (TTHM) sample results are reported to states, not to EPA's national database, so this page ranks systems by violations rather than levels.
Most violations
| Water system | People | Violations |
|---|---|---|
| City of Lindsay | 12,659 | 84 |
| Waurika Public Works Authority | 2,100 | 72 |
| Boswell Public Works Authority | 932 | 72 |
| Ryan Utilities Authority | 800 | 72 |
| Cleveland Municipal Authority | 3,262 | 71 |
| Hominy Water System | 2,584 | 69 |
| Maysville Water System | 1,212 | 69 |
| Choctaw County Rwsg & Swmd #6 | 850 | 69 |
| Stringtown Public Works Authority | 1,105 | 67 |
| Pushmataha County Rural Water District #5 (Nashoba) | 725 | 66 |
| Haskell Public Works Authority – Swp | 250 | 63 |
| Osage County Rural Water District # 5 | 561 | 62 |
| Pushmataha County Rural Water District #3 | 4,825 | 61 |
| McCurtain Municipal Authority | 560 | 59 |
| Wewoka Public Works Authority | 3,450 | 58 |
| Muskogee County Rural Water District #5 | 4,135 | 57 |
| Olustee Public Works Authority | 607 | 57 |
| Orange County Water Control & Improvement District 1 | 15,258 | 56 |
| McIntosh County Rural Water District #5 | 1,900 | 56 |
| Barnsdall Water System | 1,243 | 56 |
| Southern Okla Water Corp | 11,250 | 53 |
| Spiro East Water Association | 1,817 | 53 |
| Okmulgee Public Works Authority | 13,495 | 52 |
| Comanche Public Works Authority | 1,649 | 50 |
| Millersview Doole Water Supply Corporation | 3,987 | 49 |
States with the most systems with violations
- Texas: 499
- Oklahoma: 279
- Louisiana: 167
- Florida: 126
- Missouri: 105
- Arkansas: 99
- New York: 93
- Kansas: 89
- California: 87
- North Carolina: 85
- Kentucky: 72
- Ohio: 65
Sources
The limits, health goals and health effects on this page come from these EPA sources. The results come from EPA's monitoring data for each water system.
- EPA: National Primary Drinking Water Regulations (limits and health effects table)
- EPA ECHO: Safe Drinking Water Information System data
This page summarizes public regulatory information. It is not medical advice. How we source and check this site.
Questions
What is the safe level of Total trihalomethanes (TTHM) in drinking water?
The federal legal limit (MCL) is 80 ppb.
How do I remove Total trihalomethanes (TTHM) from tap water?
See the filter guidance on this page: look for a product certified for Total trihalomethanes (TTHM) specifically, and check the claim in NSF's certified product listings.
Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.