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National Drinking Water Database


Total trihalomethanes (TTHMs) in Washington


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

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

RankSystem Population Served Positive test results of total reported tests Average Level
(Range)
1Orient Water Company
Orient, WA
1006 of 6107.89 ppb
(62.05 to 196 ppb)
2Spring Point Homeowners Association
Deer Harbor, WA
9010 of 1392.33 ppb
(0 to 184.8 ppb)
3Eagle Cove Water Association
Friday Harbor, WA
6010 of 1091.42 ppb
(56.35 to 123.6 ppb)
4Aleck Bay Park Water System
Lopez Island, WA
367 of 785.06 ppb
(68.7 to 106.4 ppb)
5Point Roberts Water District NO 4
Point Robert, WA
1,30012 of 1283.2 ppb
(53.2 to 133.6 ppb)
6Tamoshan
Olympia, WA
2604 of 478.8 ppb
(75.8 to 86.2 ppb)
7Roche Harbor Water System Inc
Friday Harbor, WA
32925 of 2877.95 ppb
(0 to 135.9 ppb)
8Town of Friday Harbor
Friday Harbor, WA
1,99513 of 1373.87 ppb
(40.7 to 112.7 ppb)
9San Juan Ranchos
Friday Harbor, WA
287 of 870.56 ppb
(0 to 127.4 ppb)
10Cape San Juan Water District
Friday Harbor, WA
1413 of 470.08 ppb
(0 to 128.5 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

Violation Summary for Total trihalomethanes (TTHMs) in Washington

There are no violations reported for this contaminant in Washington