National Drinking Water Database
National Drinking Water Database - Chemical Contaminants
Total trihalomethanes (TTHMs)
Status: Regulated - EPA has established a maximum legal limit in tapwater for this contaminant.
Total trihalomethanes constitute the sum of four disinfection byproducts: chloroform, bromodichloromethane, dibromochloromethane, and bromoform. [read more]
Detected |
Found above health guidelines |
Found above legal limit |
|
|---|---|---|---|
| States | 46 |
45 |
41 |
| Water utilities | 25,794 |
15,425 |
4,135 |
| People Served | 236,907,123 |
206,475,520 |
53,126,324 |
Total trihalomethanes (TTHMs) Exposure by State
Water utilities in 46 states have reported detecting Total trihalomethanes (TTHMs) in treated tap water since 2004, according to EWG's analysis of water quality data supplied by state water agencies.
| State | Water Suppliers with Total trihalomethanes (TTHMs) contamination | Water suppliers reporting Total trihalomethanes (TTHMs) above health-based limits | ||
|---|---|---|---|---|
| Systems | Population | Systems | Population | |
| California | 936 | 46,123,082 | 486 | 38,126,578 |
| Texas | 3,635 | 19,620,471 | 2,390 | 17,705,817 |
| Florida | 1,707 | 18,314,986 | 1,240 | 17,145,101 |
| New York | 1,825 | 16,579,302 | 1,052 | 15,207,047 |
| Illinois | 1,476 | 12,650,186 | 1,031 | 11,847,956 |
| Pennsylvania | 1,663 | 10,758,511 | 779 | 9,889,384 |
| Ohio | 1,143 | 10,025,008 | 829 | 9,767,672 |
| New Jersey | 510 | 8,525,992 | 244 | 7,221,152 |
| Virginia | 794 | 7,329,405 | 451 | 7,112,469 |
| North Carolina | 1,457 | 7,153,943 | 927 | 6,872,592 |
| Massachusetts | 311 | 7,057,939 | 207 | 6,162,429 |
| Michigan | 488 | 5,742,051 | 273 | 5,319,041 |
| Maryland | 371 | 5,116,257 | 156 | 4,815,049 |
| Indiana | 570 | 4,484,201 | 433 | 4,216,921 |
| Kentucky | 213 | 3,639,078 | 172 | 3,502,086 |
| Missouri | 670 | 4,583,573 | 437 | 3,457,231 |
| Washington | 839 | 4,387,619 | 354 | 3,417,957 |
| Alabama | 252 | 4,031,652 | 148 | 3,216,596 |
| Arizona | 286 | 4,633,570 | 105 | 3,102,899 |
| Utah | 220 | 3,495,143 | 112 | 2,999,417 |
| Minnesota | 697 | 3,984,464 | 324 | 2,813,218 |
| Oklahoma | 636 | 2,910,505 | 510 | 2,786,112 |
| Oregon | 427 | 2,928,791 | 278 | 2,718,427 |
| Arkansas | 701 | 2,914,334 | 492 | 2,626,332 |
| Wisconsin | 609 | 3,605,153 | 212 | 2,196,553 |
| Nevada | 47 | 2,193,984 | 17 | 2,040,288 |
| Iowa | 706 | 2,403,577 | 489 | 1,906,200 |
| Nebraska | 185 | 1,138,184 | 76 | 997,752 |
| New Mexico | 334 | 1,485,475 | 148 | 970,417 |
| Rhode Island | 40 | 911,495 | 25 | 885,140 |
| Delaware | 146 | 875,080 | 75 | 729,100 |
| South Carolina | 76 | 682,992 | 29 | 584,991 |
| District of Columbia | 1 | 581,530 | 1 | 581,530 |
| New Hampshire | 317 | 650,193 | 59 | 448,427 |
| North Dakota | 188 | 436,023 | 188 | 436,023 |
| Connecticut | 2 | 431,300 | 2 | 431,300 |
| Montana | 229 | 571,260 | 130 | 426,534 |
| Maine | 178 | 598,903 | 93 | 402,562 |
| Idaho | 233 | 836,618 | 86 | 390,351 |
| Wyoming | 152 | 384,806 | 81 | 284,279 |
| Alaska | 199 | 516,074 | 132 | 248,544 |
| Vermont | 232 | 303,363 | 113 | 226,254 |
| Hawaii | 81 | 1,247,127 | 29 | 177,829 |
| South Dakota | 10 | 33,068 | 9 | 32,463 |
| Colorado | 1 | 29,500 | 1 | 29,500 |
| West Virginia | 1 | 1,355 | 0 | 0 |
| Total | 25,794 | 236,907,123 | 15,425 | 206,475,520 |
The Most Polluted Communities
25,794 water utilities reported detecting Total trihalomethanes (TTHMs) in tap water since 2004, according to EWG's analysis of water quality data supplied by state water agencies
Ranked by highest average Total trihalomethanes (TTHMs) level
| Rank | System | Population Served | Positive test results of total reported tests | Average Level (Range) |
|---|---|---|---|---|
| 1 | Brazos River Authority Possum Kingdom Dam Graford, TX | 45 | 3 of 3 | 234.67 ppb (230 to 239 ppb) |
| 2 | Twin Rivers Estates, Inc. Checotah, OK | 250 | 2 of 2 | 217.24 ppb (210.7 to 223.77 ppb) |
| 3 | Hughes Co Rwd #2 Stuart, OK | 1,083 | 6 of 6 | 211.97 ppb (200.5 to 222.6 ppb) |
| 4 | Lakeshore Sites Water Co Haskell, TX | 148 | 1 of 1 | 210.5 ppb (210.5 ppb) |
| 5 | Leflore Co Rwd #17 Hodgen, OK | 430 | 1 of 1 | 205.9 ppb (205.9 ppb) |
| 6 | Martha Martha, OK | 205 | 2 of 2 | 205.43 ppb (186.25 to 224.6 ppb) |
| 7 | Rolling Hills Subdivision Shelbyville, TX | 42 | 1 of 1 | 202 ppb (202 ppb) |
| 8 | Martin Creek Salem, VA | 495 | 1 of 1 | 200 ppb (200 ppb) |
| 9 | Delaney Court Salem, VA | 224 | 1 of 1 | 200 ppb (200 ppb) |
| 10 | Preston Shores Water System Wichita Falls, TX | 2,010 | 11 of 11 | 198.2 ppb (148 to 233 ppb) |
Health Based Limits for Total trihalomethanes (TTHMs)
| Standard | Description | Level |
|---|---|---|
| One in one million (10-6) Cancer Risk | The concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 1,000,000. Source: U.S. Environmental Protection Agency. | 9.8 ppb |
| EPA Human Health Water Quality Criteria | Water quality criteria set by the US EPA provide guidance for states and tribes authorized to establish water quality standards under the Clean Water Act (CWA) to protect human health. These are non-enforceable standards based upon exposure by both drinking water and the contribution of water contamination to other consumed foods. Source: U.S. Environmental Protection Agency. | 11.5 ppb |
| Maximum Contaminant Limit (MCL) | The enforceable standard which defines the highest level of a contaminant that is allowed in drinking water. MCLs are set as close to health-based limits (Maximum Contaminant Level Goals, or MCLGs) as feasible using the best available analytical and treatment technologies and taking cost into consideration. Source: U.S. Environmental Protection Agency. | 80 ppb |
| Lifetime health-based limit, non-cancer risk | Concentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic health effects for a lifetime of exposure. The Lifetime health-based limit (or Health Advisory, HA) is based on exposure for a a 70-kg adult consuming 2 liters of water per day. Source: U.S. Environmental Protection Agency. | 130 ppb |
| One in ten thousand (10-4) Cancer Risk | The concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 10,000. Source: U.S. Environmental Protection Agency. | 980 ppb |
| Drinking Water Equivalent Level | A lifetime exposure concentration protective of adverse, noncarcinogenic health effects, that assumes all of the exposure to a contaminant is from drinking water. Source: U.S. Environmental Protection Agency. | 1835 ppb |
| Children's health-based limit for 10-day exposure | Concentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic effects for up to ten days of exposure. The Ten-Day health-based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day. Source: U.S. Environmental Protection Agency. | 4860 ppb |
| Children's health-based limit for 1-day exposure | Concentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic health effects for up to one day of exposure. The One-Day health-based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day. Source: U.S. Environmental Protection Agency. | 10600 ppb |
Testing Summary for Total trihalomethanes (TTHMs)
| Are tests routinely required for Total trihalomethanes (TTHMs) by federal law? | Yes |
| Water suppliers reporting tests for Total trihalomethanes (TTHMs) (2004-2009): | 37,735 of 47,576 |
| Average testing rate for water supplier reporting tests (2004-2009): | 1.0 per year |
Violation Summary for Total trihalomethanes (TTHMs)
Data from the U.S. Environmental Protection Agency includes the following violations of federal standards for Total trihalomethanes (TTHMs) since 2004
| Maximum Contaminant Level Exceedance Violations | 10,529 |
| Monitoring Violations | 263 |
| Reporting Violations | 6 |