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Total trihalomethanes (TTHMs) in Washington

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Total trihalomethanes constitute the sum of four disinfection byproducts: chloroform, bromodichloromethane, dibromochloromethane, and bromoform. [read more]

Total Trihalomethanes (TTHMs) Trihalomethanes (THMs) are byproducts of chlorinated disinfectants added to drinking water to control pathogens. They are formed when chlorine or chloramine react with organic matter found in source water. Trihalomethanes are known to be genotoxic (causing DNA damge) and carcinogenic (Richardson 2007). the International Agency for Research on Cancer (IARC) classifies two THMs, chloroform and bromodichloromethane, as possibly carcinogenic to humans (IARC 2008b). Exposure to trihalomethanes in drinking water has been linked to liver, kidney or central nervous system problems, and to increased risk of bladder cancer (Villanueva 2007; U.S. Environmental Protection Agency (USEPA) 2009b). EPA drinking water standards allow up to 0.08 mg/L (parts per million) of total trihalomethanes in tap water (the so-called Maximum Contaminant Level or MCL). For each of the four trihalomethanes, EPA also set the Maximum Contaminant Level Goal (MCLG), which is the level of a contaminant in drinking water below which there is no known or expected risk to health. The MCLGs are set for: bromodichloromethane (zero); bromoform (zero); dibromochloromethane (0.06 mg/L): chloroform (0.07 mg/L) (USEPA 2009b).

The Most Polluted Communities in Washington

839 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	Orient Water Company Orient, WA	100	6 of 6	107.89 ppb (62.05 to 196 ppb)
2	Spring Point Homeowners Association Deer Harbor, WA	90	10 of 13	92.33 ppb (0 to 184.8 ppb)
3	Eagle Cove Water Association Friday Harbor, WA	60	10 of 10	91.42 ppb (56.35 to 123.6 ppb)
4	Aleck Bay Park Water System Lopez Island, WA	36	7 of 7	85.06 ppb (68.7 to 106.4 ppb)
5	Point Roberts Water District NO 4 Point Robert, WA	1,300	12 of 12	83.2 ppb (53.2 to 133.6 ppb)
6	Tamoshan Olympia, WA	260	4 of 4	78.8 ppb (75.8 to 86.2 ppb)
7	Roche Harbor Water System Inc Friday Harbor, WA	329	25 of 28	77.95 ppb (0 to 135.9 ppb)
8	Town of Friday Harbor Friday Harbor, WA	1,995	13 of 13	73.87 ppb (40.7 to 112.7 ppb)
9	San Juan Ranchos Friday Harbor, WA	28	7 of 8	70.56 ppb (0 to 127.4 ppb)
10	Cape San Juan Water District Friday Harbor, WA	141	3 of 4	70.08 ppb (0 to 128.5 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

Violation Summary for Total trihalomethanes (TTHMs) in Washington

There are no violations reported for this contaminant in Washington