Menu

EWG's Tap Water Database — 2019 UPDATE

Donate

Total trihalomethanes (TTHMs)

Status: National drinking water standard exists

 

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform. Read More.

Studies conducted in the U.S. and Europe have found that drinking tap water that carries disinfection byproducts increases the risk of developing bladder cancer. In animal studies, all trihalomethanes cause liver, kidney and intestinal tumors. Some human epidemiological studies also reported an association between disinfection byproducts and an increased risk of problems during pregnancy, including spontaneous miscarriage, cardiovascular defects, neural tube defects and low birth weight.

In 2010, the California Office of Environmental Health Hazard Assessment published a draft public health goal for the trihalomethanes group at 0.8 parts per billion, or 100 times lower than the federal legal limit of 80 parts per billion for this contaminant group.

Click here to read more about disinfection byproducts.

2015-2017:

FOUND
FOUND ABOVE HEALTH GUIDELINES

50

states detected

31,748

utilities detected

289 million

people served

50

states over health guideline

31,638

utilities over health guideline

287 million

people served over health guideline

Health concerns for trihalomethanes

Bladder cancer

Skin cancer

Harm to fetal growth and development

State and national drinking water standards and health guidelines

EWG Health Guideline 0.15 ppb

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

EPA Maximum Contaminant
Level (MCL) 80 ppb

The legal limit for the group of four trihalomethanes, established in 1998, was based on the need for residual disinfectant levels in water served to customers and the cost of treatment. This limit does not fully protect against the risk of cancer due to exposure to trihalomethanes.

ppb = parts per billion

States reporting trihalomethanes in drinking water

UTILITIES REPORTING ABOVE HEALTH GUIDELINES UTILITIES WITH CONTAMINATION
State UtilitiesPeople Served UtilitiesPeople Served
California1,37939,566,8821,38439,707,086
Texas3,55526,350,7923,55526,350,792
New York1,75519,980,9421,76920,575,160
Florida1,48919,613,7151,49619,688,660
Illinois1,57512,809,0091,57512,809,009
Pennsylvania1,52010,420,1631,52310,424,213
Ohio1,0629,995,8591,06510,060,174
Georgia7669,071,0347699,074,700
North Carolina1,0097,676,1451,0097,676,145
Tennessee4397,086,5644397,086,564
Michigan7267,001,2237267,001,223
Virginia7606,922,5097646,924,815
Massachusetts3506,514,9223566,524,878
Arizona4166,269,5354196,286,139
Washington1,0165,589,9141,0295,627,773
Colorado7845,569,2617855,572,409
Alabama4895,484,3364915,520,132
Maryland3825,311,9153825,311,915
New Jersey1994,995,0152024,998,642
Louisiana9064,895,3539194,936,714
Indiana5934,859,4475934,859,447
Missouri7074,856,1757074,856,175
Kentucky3754,609,3303764,609,404
Minnesota6634,087,2526794,136,672
Wisconsin5693,922,8255713,924,451
South Carolina3593,737,0993603,782,240
Oregon4143,717,2554143,717,255
Oklahoma8073,529,7358073,529,735
Arkansas6033,087,9746043,089,814
Utah2582,686,9412652,765,574
Kansas7912,731,1197912,731,119
Connecticut2272,666,9632272,666,963
Nevada1112,562,3731112,562,373
Iowa7062,512,8137062,512,813
Mississippi5852,144,6645852,144,664
New Mexico3451,778,6713471,779,345
West Virginia4191,534,3554191,534,355
Hawaii991,402,667991,402,667
Nebraska1461,300,3271511,326,125
Rhode Island441,007,522441,007,522
Idaho203926,198208986,503
Delaware125976,597125976,597
New Hampshire265780,936267782,270
South Dakota291703,488291703,488
North Dakota290695,774290695,774
District Of Columbia4664,5724664,572
Maine169620,844170620,879
Alaska179614,103179614,103
Montana263579,343260579,143
Vermont247473,769246473,154
Wyoming204427,986195424,521
MORE
LESS

Filtering technologies that reduce trihalomethanes

carbon filter icon

Activated Carbon

reverse osmosis icon

Reverse Osmosis

Utilities with the highest amounts of trihalomethanes, 2015-2017

ALL UTILITIES
LARGE UTILITIES
UtilityLocationTestsAverage levelPeople served
Country Estates Water System SouthWest Monroe, LA1 of 1395.3 ppb600
Pleasant Hills-crossroads Water SystemsJoyce, LA32 of 32343.3 ppb840
Concord Water SystemMarion, LA40 of 40295.8 ppb426
Wards Chapel Water SystemFarmerville, LA44 of 44280.8 ppb1,350
Elmdale, City ofElmdale, KS1 of 1270.0 ppb53
Village of Calvin Water SystemCalvin, LA24 of 24264.1 ppb591
Litroe Water SystemMarion, LA48 of 48261.9 ppb369
Oxbow Mining Waterworks*Somerset, CO1 of 1257.0 ppb200
Southwest Ouachita Waterworks Inc.West Monroe, LA40 of 40248.1 ppb10,092
Walnut Ridge Estates Water SystemZavalla, TX8 of 8245.9 ppb178
Vixen Water System WestChatham, LA40 of 40245.0 ppb288
Asher Utility Dev AuthorityAsher, OK10 of 10241.1 ppb375
Town of Plain Dealing Water SystemPlain Dealing, LA44 of 44237.8 ppb2,733
Boswell Public Works AuthorityBoswell, OK18 of 18232.5 ppb932
Holmesville Water System*Downsville, LA48 of 48228.3 ppb2,310
Highway 84 West Water SupplyWinnfield, LA40 of 40226.8 ppb499
Linville-haile Water SystemMarion, LA46 of 46219.2 ppb1,635
La Playa Subdivision Water SystemKirbyville, TX6 of 6217.2 ppb59
Millersview-doole Water Supply Corporation*Millersview, TX19 of 19216.3 ppb3,987
Mountain Park Public Works AuthorityMountain Park, OK9 of 9214.9 ppb473
Town of Friars PointFriars Point, MS1 of 1209.0 ppb1,200
Anthony Harbor SubdivisionLufkin, TX10 of 10206.9 ppb109
Osage County Rural Water District # 20 (hulah)Bartlesville, OK10 of 10205.7 ppb350
Village of Georgetown Water SupplyGeorgetown, LA48 of 48204.7 ppb302
Jones Mcginty Water SystemJones, LA48 of 48203.5 ppb801
Beechwood Water Supply CorporationHemphill, TX16 of 16202.8 ppb1,143
Country Estates Water System NorthWest Monroe, LA36 of 36202.4 ppb597
Vixen Water System EastChatham, LA32 of 32200.2 ppb486
Lakewood Water SystemLufkin, TX11 of 11198.8 ppb42
Thorne Bay, City ofThorne Bay, AK11 of 11198.6 ppb470
Ryan Utilities AuthorityRyan, OK22 of 22196.8 ppb800
Wanette Public Works AuthorityWanette, OK10 of 10192.8 ppb402
Union Parish Waterworks District 1Farmerville, LA40 of 40191.8 ppb1,626
Sardis Water SystemGilbert, LA48 of 48191.6 ppb1,404
Fairview Union Water System*Campti, LA48 of 48188.5 ppb2,205
Otoe-missouria TribeRed Rock, OK10 of 10187.5 ppb250
Turtle Cove Lot Owners AssociationFreeport, TX11 of 11187.3 ppb66
Hudson Gaars Mill Water SystemSikes, LA28 of 28186.3 ppb660
Severy, City ofSevery, KS12 of 12185.0 ppb241
Fcsa #30/el PorvenirFresno, CA11 of 11184.5 ppb130
City of NomeNome, TX20 of 20184.3 ppb753
Pappas & Company (mendota)Mendota, CA11 of 12184.2 ppb25
Pappas & Company (coalinga)Mendota, CA12 of 12182.2 ppb25
Osage County Rural Water District # 5Barnsdall, OK21 of 21181.4 ppb561
Waurika Public Works Authority*Waurika, OK21 of 21180.8 ppb2,100
Joyce Water SupplyCovington, LA44 of 44176.1 ppb474
Cleveland Municipal AuthorityCleveland, OK23 of 23175.8 ppb3,262
Red Hill Waterworks Inc.*Georgetown, LA48 of 48175.4 ppb1,872
Commodore Cove Improvement DistrictFreeport, TX9 of 9174.5 ppb495
Ramsey Water SystemWest Monroe, LA32 of 32172.1 ppb60

* This water utility supplies finished drinking water to at least one other water utility. The purchasing utility is not required to test for or report Total trihalomethanes (TTHMs), but it likely has the contaminant in its water supply.

UtilityLocationTestsAverage levelPeople served
Southwest Ouachita Waterworks Inc.West Monroe, LA40 of 40248.1 ppb10,092
Duncan Public Utilities Authority*Duncan, OK48 of 48150.6 ppb23,000
City of LemooreLemoore, CA47 of 48117.2 ppb24,945
Walnut Creek SUD*Springtown, TX48 of 48108.6 ppb23,807
Tri County Joint Municipal Authority*Fredericktown, PA48 of 4893.2 ppb10,100
Claremore*Claremore, OK52 of 5291.4 ppb15,873
Orange County WCID 1Vidor, TX48 of 4890.1 ppb17,773
Okmulgee*Okmulgee, OK48 of 4886.3 ppb13,495
Altus*Altus, OK47 of 4784.2 ppb21,477
Union CityUnion City, GA12 of 1283.7 ppb18,636
Suisun-Solano Water AuthorityVacaville, CA3 of 382.3 ppb28,856
Military Highway WSC - Las Rusias WTPProgreso, TX42 of 4280.0 ppb14,292
Marshall*Marshall, MO46 of 4679.9 ppb13,065
City of Port Lavaca*Port Lavaca, TX48 of 4879.7 ppb12,248
City of Temple*Temple, TX96 of 9679.3 ppb69,180
Exeter Water DepartmentExeter, NH38 of 3878.6 ppb11,000
Martin County Water District #1Inez, KY34 of 3476.8 ppb10,843
Southern Okla Water CorpArdmore, OK36 of 4576.2 ppb11,250
City of Winter SpringsWinter Springs, FL52 of 5275.5 ppb35,996
Chickasha Municipal Authority*Chickasha, OK48 of 4875.1 ppb16,036
Rogers County Rural Water District # 3 Lake PlantClaremore, OK24 of 2474.9 ppb10,470
Norwich Public Utilities*Norwich, CT82 of 8274.8 ppb36,067
Pikeville Water Department*Pikeville, KY56 of 5874.1 ppb12,700
R. C. Willis WTP (City of Palatka)Palatka, FL48 of 4874.1 ppb11,900
Nueces County WCID 3*Robstown, TX48 of 4873.7 ppb14,607
City of Sacramento Main*Sacramento, CA3 of 373.0 ppb486,189
Greenup Water System*Greenup, KY53 of 5372.7 ppb12,193
Magoffin County Water DistrictSalyersville, KY24 of 2472.5 ppb10,294
Bridgeport TownshipBridgeport, MI17 of 1772.0 ppb10,514
Sapulpa*Sapulpa, OK48 of 4871.9 ppb19,702
Dartmouth Water DivisionDartmouth, MA105 of 10571.3 ppb24,081
Brownville Water SystemWest Monroe, LA36 of 3670.9 ppb10,872
City of Beeville*Beeville, TX48 of 4870.9 ppb15,039
Buchanan County PSA*Vansant, VA48 of 4870.7 ppb19,205
Southern Water & Sewer District*Mcdowell, KY51 of 5170.5 ppb22,480
Longmeadow Water DepartmentLongmeadow, MA88 of 8870.2 ppb14,552
Washington Water Authority WWAFarmington, AR48 of 4870.2 ppb15,734
Assumption Parish Waterworks District 1*Napoleonville, LA96 of 9670.0 ppb22,862
South Granville Water and Sewer AuthorityButner, NC51 of 5169.6 ppb19,219
Plainfield TownshipGrand Rapids, MI35 of 3569.4 ppb40,891
Hudson Water Supply CorporationLufkin, TX20 of 2069.0 ppb10,211
City of Kerrville*Kerrville, TX48 of 4868.7 ppb22,907
Albany Water Works*Albany, KY48 of 4868.7 ppb14,702
Cannonsburg Water District*Ashland, KY40 of 4068.7 ppb10,692
Eatonton Putnam Water & Sewer AuthorityEatonton, GA24 of 2468.7 ppb12,561
Harrisburg*Harrisburg, NC48 of 4868.6 ppb14,633
City of CalexicoCalexico, CA26 of 2668.4 ppb38,572
City of Laredo*Laredo, TX96 of 9668.3 ppb259,113
Halifax Co--Halifax*Roanoke Rapids, NC48 of 4868.1 ppb19,762
Placer CWA - Auburn/BowmanAuburn, CA3 of 367.8 ppb28,588

* This water utility supplies finished drinking water to at least one other water utility. The purchasing utility is not required to test for or report Total trihalomethanes (TTHMs), but it likely has the contaminant in its water supply.