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.

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.

Click here to read more about disinfection byproducts.

2017-2019:

FOUND

FOUND ABOVE HEALTH GUIDELINES

FOUND ABOVE LEGAL LIMIT

states detected

32,247

utilities detected

296 million

people served

states over health guideline

32,136

utilities over health guideline

295 million

people served over health guideline

states over legal limit

410

utilities over legal limit

585,000

people served over legal limit

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

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	Utilities	People Served		Utilities	People Served
California		1,426	37,886,924			1,430	38,029,122
Texas		3,531	27,125,981			3,532	27,146,552
New York		1,770	20,426,615			1,788	20,822,132
Florida		1,468	20,404,021			1,473	20,436,531
Illinois		1,585	12,165,999			1,585	12,165,999
Pennsylvania		1,471	11,226,312			1,472	11,226,637
Ohio		1,039	10,043,492			1,039	10,043,492
Georgia		777	9,044,026			778	9,045,011
New Jersey		497	8,799,525			500	8,799,725
North Carolina		982	8,529,077			982	8,529,077
Tennessee		437	7,135,210			437	7,135,210
Michigan		805	7,059,442			806	7,060,139
Virginia		751	6,970,116			753	6,974,461
Massachusetts		368	6,554,803			372	6,570,251
Colorado		812	6,312,294			813	6,312,359
Arizona		420	6,295,843			424	6,305,952
Washington		1,004	6,011,637			1,013	6,025,555
Alabama		485	5,845,126			487	5,862,781
Maryland		379	5,314,686			379	5,314,686
Louisiana		917	4,914,916			931	4,954,595
Missouri		740	4,930,482			741	4,941,482
Indiana		592	4,897,229			592	4,897,229
Kentucky		373	4,478,682			373	4,478,682
Minnesota		655	4,279,311			671	4,290,804
South Carolina		383	3,997,299			383	3,997,299
Wisconsin		562	3,909,736			566	3,925,137
Oregon		434	3,815,197			436	3,820,141
Oklahoma		780	3,587,341			780	3,587,341
Utah		291	3,032,079			293	3,038,029
Kansas		806	2,862,208			807	2,874,265
Arkansas		595	2,805,353			596	2,807,079
Nevada		109	2,762,819			110	2,763,149
Connecticut		232	2,667,212			232	2,667,212
Iowa		752	2,579,237			752	2,579,237
Mississippi		550	2,076,364			550	2,076,364
New Mexico		365	1,915,976			365	1,915,976
West Virginia		409	1,553,361			409	1,553,361
Hawaii		94	1,427,338			95	1,432,254
Nebraska		159	1,289,795			163	1,295,996
Delaware		122	980,714			122	980,714
Rhode Island		44	969,111			44	969,111
Idaho		195	818,052			201	855,431
New Hampshire		280	791,468			286	801,729
South Dakota		309	698,755			309	698,755
North Dakota		289	687,937			289	687,937
District Of Columbia		4	664,572			4	664,572
Alaska		181	616,097			182	617,090
Maine		172	612,946			175	613,572
Montana		273	594,854			273	595,529
Vermont		252	477,556			252	477,556
Wyoming		210	455,614			202	452,361

LESS

Filtering technologies that reduce trihalomethanes

Utilities with the highest amounts of trihalomethanes, 2017-2019

ALL UTILITIES

LARGE UTILITIES

Utility	Location	Tests	Average level	People served
Pleasant Hills-crossroads Water Systems	Joyce, LA	62 of 62	333.0 ppb	840
Village of Calvin Water System	Calvin, LA	60 of 60	282.5 ppb	591
Wards Chapel Water System	Farmerville, LA	92 of 92	273.6 ppb	1,350
Concord Water System	Marion, LA	88 of 88	271.9 ppb	426
Litroe Water System	Marion, LA	96 of 96	264.5 ppb	369
Asher Utility Dev Authority	Asher, OK	20 of 20	232.6 ppb	375
Eagle Lakes WTP	Bunnell, FL	4 of 4	231.3 ppb	231
Vixen Water System West	Chatham, LA	90 of 90	227.9 ppb	288
Jones Mcginty Water System	Jones, LA	96 of 96	223.4 ppb	801
Hudson Gaars Mill Water System	Dodson, LA	70 of 70	214.9 ppb	660
Town of Plain Dealing Water System	Plain Dealing, LA	88 of 88	214.4 ppb	2,733
Linville-haile Water System	Marion, LA	92 of 94	203.4 ppb	1,635
Highway 84 West Water Supply	Winnfield, LA	88 of 88	201.1 ppb	499
Mountain Park Public Works Authority	Mountain Park, OK	18 of 18	200.5 ppb	473
Osage County Rural Water District # 20 (hulah)	Bartlesville, OK	20 of 20	194.9 ppb	350
Lakewood Water System	Lufkin, TX	21 of 21	194.4 ppb	42
Walnut Ridge Estates Water System	Zavala, TX	16 of 17	194.3 ppb	134
Sardis Water System	Gilbert, LA	96 of 96	193.2 ppb	1,404
Ryan Utilities Authority	Ryan, OK	42 of 42	192.9 ppb	800
Vixen Water System East	Chatham, LA	72 of 72	191.6 ppb	486
Village of Georgetown Water Supply	Georgetown, LA	96 of 96	189.0 ppb	302
Thorne Bay, City of	Thorne Bay, AK	21 of 22	188.7 ppb	470
La Playa Subdivision Water System	Kirbyville, TX	14 of 14	185.2 ppb	59
Wanette Public Works Authority	Wanette, OK	19 of 19	185.0 ppb	402
Turtle Cove Lot Owners Association	Freeport, TX	21 of 21	184.2 ppb	66
Boswell Public Works Authority	Boswell, OK	38 of 38	182.0 ppb	932
Cleveland Municipal Authority	Cleveland, OK	41 of 41	181.2 ppb	3,262
Pappas & Company (mendota)	Mendota, CA	23 of 24	180.8 ppb	25
Fcsa #30/el Porvenir	Fresno, CA	24 of 24	178.8 ppb	130
Country Estates Water System South	West Monroe, LA	14 of 14	178.4 ppb	600
Country Estates Water System North	West Monroe, LA	72 of 72	177.5 ppb	597
Fairview Union Water System*	Coushatta, LA	96 of 96	177.1 ppb	2,205
Chesapeake Shores	Rockville, VA	4 of 4	176.0 ppb	56
Anthony Harbor Subdivision	Lufkin, TX	19 of 19	174.2 ppb	109
Waurika Public Works Authority*	Waurika, OK	47 of 47	173.7 ppb	2,100
Grayhorse Rural Water District	Fairfax, OK	22 of 22	166.7 ppb	100
Fcsa #32/cantua Creek	Fresno, CA	23 of 23	166.6 ppb	250
Beechwood Water Supply Corporation	Hemphill, TX	31 of 31	166.0 ppb	1,372
Chatham Water System	Chatham, LA	88 of 100	165.6 ppb	1,137
Red Hill Waterworks Inc.*	Georgetown, LA	96 of 96	164.5 ppb	1,872
Darling Water Association	Darling, MS	1 of 1	161.7 ppb	240
Ramsey Water System	West Monroe, LA	62 of 62	159.6 ppb	60
City of Strawn	Strawn, TX	24 of 24	158.8 ppb	696
Sandy Point 480 Water System	Campti, LA	74 of 78	158.5 ppb	675
Oxbow Mining Waterworks*	Somerset, CO	2 of 2	157.2 ppb	7
Severy, City of	Severy, KS	22 of 22	156.7 ppb	230
Marion Water System*	Marion, LA	92 of 92	156.0 ppb	1,146
Backwood Village Water System	Saline, LA	68 of 70	155.8 ppb	783
Rra Preston Shores Water System*	Wichita Falls, TX	44 of 44	155.1 ppb	2,037
Holmesville Water System*	Downsville, LA	98 of 98	155.1 ppb	2,310

* 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.

Utility	Location	Tests	Average level	People served
Southwest Ouachita Waterworks Inc.	West Monroe, LA	106 of 108	128.4 ppb	10,092
Duncan Public Utilities Authority*	Duncan, OK	96 of 96	126.1 ppb	23,000
City of Lemoore	Lemoore, CA	87 of 88	120.0 ppb	24,945
Tri County Joint Municipal Authority*	Fredericktown, PA	95 of 96	87.0 ppb	10,100
Okmulgee*	Okmulgee, OK	100 of 100	86.2 ppb	13,495
Walnut Creek SUD*	Springtown, TX	96 of 96	86.2 ppb	23,118
Orange County WCID 1	Vidor, TX	96 of 96	84.5 ppb	16,448
Claremore*	Claremore, OK	100 of 100	82.1 ppb	15,873
R. C. Willis WTP (City of Palatka)	Palatka, FL	96 of 96	80.8 ppb	11,900
Tuskegee Utilities Board*	Tuskegee, AL	103 of 103	76.4 ppb	12,510
City of Port Lavaca*	Port Lavaca, TX	92 of 92	75.8 ppb	12,248
Altus*	Altus, OK	91 of 91	74.5 ppb	21,477
Longmeadow Water Department	Longmeadow, MA	152 of 152	73.2 ppb	15,701
Exeter Water Department	Exeter, NH	74 of 75	73.2 ppb	11,000
Bloomfield Water Department	Bloomfield, NJ	96 of 96	72.2 ppb	47,315
Chickasha Municipal Authority*	Chickasha, OK	100 of 100	71.9 ppb	16,036
Greenup Water System*	Greenup, KY	129 of 129	71.7 ppb	12,193
Hudson Water Supply Corporation	Lufkin, TX	46 of 46	71.2 ppb	10,211
Lincoln Park Water Department*	Lincoln Park, NJ	96 of 96	70.9 ppb	11,000
Hannibal	Hannibal, MO	96 of 96	70.5 ppb	17,916
Military Highway WSC - Las Rusias WTP	Progreso, TX	81 of 81	69.9 ppb	14,292
City of Kerrville*	Kerrville, TX	96 of 96	69.6 ppb	22,217
Norwich Public Utilities*	Norwich, CT	146 of 146	69.6 ppb	36,067
Marshall*	Marshall, MO	96 of 96	69.5 ppb	13,065
Rogers County Rural Water District # 3 Lake Plant	Claremore, OK	52 of 52	69.1 ppb	10,470
Belleville Water Department*	Belleville, NJ	96 of 96	68.8 ppb	35,129
City of Calexico	Calexico, CA	73 of 74	68.7 ppb	38,572
City of Sacramento Main*	Sacramento, CA	6 of 6	68.5 ppb	486,189
Big Sandy Water District*	Catlettsburg, KY	98 of 98	68.4 ppb	13,044
Dartmouth Water Division	Dartmouth, MA	176 of 176	68.1 ppb	24,272
N.S. Mayport	Mayport, FL	109 of 109	68.0 ppb	20,500
Albany Water Works*	Albany, KY	96 of 96	67.9 ppb	14,702
Southern Water & Sewer District*	Mcdowell, KY	102 of 102	67.3 ppb	22,480
Assumption Parish Waterworks District 1*	Napoleonville, LA	194 of 194	67.2 ppb	22,862
East Longmeadow DPW Water Department	East Longmeadow, MA	160 of 160	67.1 ppb	16,162
Southern Okla Water Corp	Ardmore, OK	77 of 93	67.0 ppb	11,250
City of Winter Park	Winter Park, FL	92 of 92	67.0 ppb	82,984
Placer CWA - Auburn/Bowman	Auburn, CA	4 of 4	66.9 ppb	28,588
City of Mercedes*	Mercedes, TX	95 of 95	66.6 ppb	15,700
Barrow County Water System*	Winder, GA	47 of 47	66.5 ppb	14,043
Orange County Utilities Department (OCUD) - East	Orlando, FL	144 of 144	66.4 ppb	290,878
Marshall County Water Corp*	Madill, OK	96 of 96	66.2 ppb	14,717
Yankton	Yankton, SD	96 of 96	66.2 ppb	14,700
City of Temple*	Temple, TX	192 of 192	66.1 ppb	85,884
Mountain Water District #1 Marrow Bone*	Pikeville, KY	96 of 96	65.9 ppb	48,286
James Fork Regional Water District*	Greenwood, AR	96 of 96	65.8 ppb	11,538
Sapulpa*	Sapulpa, OK	96 of 96	65.8 ppb	19,702
Buchanan County PSA*	Vansant, VA	96 of 96	65.5 ppb	19,326
Warren City PWS*	Cortland, OH	96 of 96	65.5 ppb	46,832
City of Plant City Utility*	Plant City, FL	109 of 109	65.5 ppb	36,889