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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.

StateWater Suppliers with Total trihalomethanes (TTHMs) contaminationWater suppliers reporting Total trihalomethanes (TTHMs) above health-based limits
SystemsPopulationSystemsPopulation
California93646,123,08248638,126,578
Texas3,63519,620,4712,39017,705,817
Florida1,70718,314,9861,24017,145,101
New York1,82516,579,3021,05215,207,047
Illinois1,47612,650,1861,03111,847,956
Pennsylvania1,66310,758,5117799,889,384
Ohio1,14310,025,0088299,767,672
New Jersey5108,525,9922447,221,152
Virginia7947,329,4054517,112,469
North Carolina1,4577,153,9439276,872,592
Massachusetts3117,057,9392076,162,429
Michigan4885,742,0512735,319,041
Maryland3715,116,2571564,815,049
Indiana5704,484,2014334,216,921
Kentucky2133,639,0781723,502,086
Missouri6704,583,5734373,457,231
Washington8394,387,6193543,417,957
Alabama2524,031,6521483,216,596
Arizona2864,633,5701053,102,899
Utah2203,495,1431122,999,417
Minnesota6973,984,4643242,813,218
Oklahoma6362,910,5055102,786,112
Oregon4272,928,7912782,718,427
Arkansas7012,914,3344922,626,332
Wisconsin6093,605,1532122,196,553
Nevada472,193,984172,040,288
Iowa7062,403,5774891,906,200
Nebraska1851,138,18476997,752
New Mexico3341,485,475148970,417
Rhode Island40911,49525885,140
Delaware146875,08075729,100
South Carolina76682,99229584,991
District of Columbia1581,5301581,530
New Hampshire317650,19359448,427
North Dakota188436,023188436,023
Connecticut2431,3002431,300
Montana229571,260130426,534
Maine178598,90393402,562
Idaho233836,61886390,351
Wyoming152384,80681284,279
Alaska199516,074132248,544
Vermont232303,363113226,254
Hawaii811,247,12729177,829
South Dakota1033,068932,463
Colorado129,500129,500
West Virginia11,35500
Total25,794236,907,12315,425206,475,520

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

RankSystem Population Served Positive test results of total reported tests Average Level
(Range)
1Brazos River Authority Possum Kingdom Dam
Graford, TX
453 of 3234.67 ppb
(230 to 239 ppb)
2Twin Rivers Estates, Inc.
Checotah, OK
2502 of 2217.24 ppb
(210.7 to 223.77 ppb)
3Hughes Co Rwd #2
Stuart, OK
1,0836 of 6211.97 ppb
(200.5 to 222.6 ppb)
4Lakeshore Sites Water Co
Haskell, TX
1481 of 1210.5 ppb
(210.5 ppb)
5Leflore Co Rwd #17
Hodgen, OK
4301 of 1205.9 ppb
(205.9 ppb)
6Martha
Martha, OK
2052 of 2205.43 ppb
(186.25 to 224.6 ppb)
7Rolling Hills Subdivision
Shelbyville, TX
421 of 1202 ppb
(202 ppb)
8Martin Creek
Salem, VA
4951 of 1200 ppb
(200 ppb)
9Delaney Court
Salem, VA
2241 of 1200 ppb
(200 ppb)
10Preston Shores Water System
Wichita Falls, TX
2,01011 of 11198.2 ppb
(148 to 233 ppb)

Health Based Limits for Total trihalomethanes (TTHMs)

StandardDescriptionLevel
One in one million (10-6) Cancer RiskThe 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 CriteriaWater 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 riskConcentration 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 RiskThe 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 LevelA 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 exposureConcentration 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 exposureConcentration 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 Violations10,529
Monitoring Violations263
Reporting Violations6