Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

City of Tacoma

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.

 

284

Samples

0

Samples exceeding legal limit (MCL)

282

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20188.78 ppb56562.00 ppb - 26.2 ppb
201912.1 ppb5149ND - 25.6 ppb
2020N/A00N/A
202110.1 ppb55550.900 ppb - 24.0 ppb
202210.5 ppb53530.610 ppb - 23.4 ppb
20239.05 ppb69690.280 ppb - 18.5 ppb

ppb = parts per billion

State, National, and Health Guidelines for Drinking Water

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

All test results

Date Lab ID Result
2018-01-028.20 ppb
2018-01-028.30 ppb
2018-01-0211.2 ppb
2018-01-027.10 ppb
2018-01-026.25 ppb
2018-01-026.68 ppb
2018-01-0210.2 ppb
2018-01-027.00 ppb
2018-01-029.00 ppb
2018-01-029.00 ppb
2018-01-025.25 ppb
2018-01-036.19 ppb
2018-01-032.00 ppb
2018-01-032.85 ppb
2018-01-034.72 ppb
2018-04-026.30 ppb
2018-04-029.10 ppb
2018-04-0210.2 ppb
2018-04-027.80 ppb
2018-04-027.80 ppb
2018-04-029.90 ppb
2018-04-027.70 ppb
2018-04-0210.1 ppb
2018-04-027.70 ppb
2018-04-029.00 ppb
2018-04-023.84 ppb
2018-04-025.69 ppb
2018-04-033.43 ppb
2018-04-036.00 ppb
2018-07-026.76 ppb
2018-07-028.80 ppb
2018-07-028.70 ppb
2018-07-023.12 ppb
2018-07-023.60 ppb
2018-07-026.58 ppb
2018-07-027.17 ppb
2018-07-037.95 ppb
2018-07-0310.6 ppb
2018-07-037.43 ppb
2018-07-038.60 ppb
2018-07-0310.9 ppb
2018-07-038.80 ppb
2018-07-0314.3 ppb
2018-07-038.05 ppb
2018-10-3011.6 ppb
2018-10-3013.7 ppb
2018-10-3014.1 ppb
2018-10-3011.2 ppb
2018-10-3012.7 ppb
2018-10-3111.1 ppb
2018-10-3112.5 ppb
2018-10-3126.2 ppb
2018-10-3112.4 ppb
2018-10-3112.4 ppb
2018-10-3112.5 ppb
2018-10-3111.3 ppb
2019-01-02ND
2019-01-149.20 ppb
2019-01-1414.6 ppb
2019-01-148.80 ppb
2019-01-1421.9 ppb
2019-01-148.20 ppb
2019-01-1413.7 ppb
2019-01-148.60 ppb
2019-01-148.50 ppb
2019-01-148.30 ppb
2019-01-1410.9 ppb
2019-01-147.30 ppb
2019-01-157.30 ppb
2019-04-0111.0 ppb
2019-04-0110.7 ppb
2019-04-0113.4 ppb
2019-04-0110.6 ppb
2019-04-019.80 ppb
2019-04-019.60 ppb
2019-04-0113.5 ppb
2019-04-019.60 ppb
2019-04-0110.00 ppb
2019-04-0113.2 ppb
2019-04-0110.00 ppb
2019-04-038.30 ppb
2019-07-088.50 ppb
2019-07-089.60 ppb
2019-07-0812.5 ppb
2019-07-089.60 ppb
2019-07-089.40 ppb
2019-07-089.70 ppb
2019-07-0813.6 ppb
2019-07-089.80 ppb
2019-07-0813.5 ppb
2019-07-0812.5 ppb
2019-07-0810.00 ppb
2019-07-089.10 ppb
2019-07-240.770 ppb
2019-10-0119.0 ppb
2019-10-0120.0 ppb
2019-10-0119.0 ppb
2019-10-0117.0 ppb
2019-10-0212.9 ppb
2019-10-0219.2 ppb
2019-10-0225.6 ppb
2019-10-0218.2 ppb
2019-10-0221.3 ppb
2019-10-0225.2 ppb
2019-10-0214.8 ppb
2019-10-0217.2 ppb
2019-12-03ND
2021-01-0440612245.54 ppb
2021-01-0440612226.60 ppb
2021-01-0440612289.50 ppb
2021-01-0440612266.62 ppb
2021-01-0440612316.52 ppb
2021-01-0440612275.43 ppb
2021-01-04406122911.3 ppb
2021-01-0440612325.01 ppb
2021-01-0440612235.17 ppb
2021-01-0440612307.19 ppb
2021-01-0440612256.59 ppb
2021-01-0540612336.75 ppb
2021-04-0540993788.83 ppb
2021-04-05409938610.4 ppb
2021-04-0540993799.87 ppb
2021-04-0540993877.29 ppb
2021-04-0540993859.08 ppb
2021-04-0540993888.42 ppb
2021-04-05409937710.1 ppb
2021-04-0540993829.28 ppb
2021-04-05409938412.5 ppb
2021-04-0540993818.61 ppb
2021-04-05409938313.0 ppb
2021-04-06409938010.7 ppb
2021-06-2142337730.900 ppb
2021-07-06414516410.7 ppb
2021-07-0641451689.22 ppb
2021-07-0641451589.69 ppb
2021-07-0641451668.60 ppb
2021-07-0641451657.90 ppb
2021-07-0641451638.22 ppb
2021-07-06414516211.3 ppb
2021-07-0641451595.08 ppb
2021-07-0641451608.25 ppb
2021-07-0741451734.67 ppb
2021-07-0741451754.76 ppb
2021-07-07414517010.7 ppb
2021-07-07414516114.1 ppb
2021-07-07414517212.8 ppb
2021-07-0741451769.05 ppb
2021-10-04419846612.2 ppb
2021-10-04419845724.0 ppb
2021-10-04419845517.2 ppb
2021-10-04419843615.4 ppb
2021-10-04419846313.9 ppb
2021-10-04419846013.1 ppb
2021-10-04419844214.8 ppb
2021-10-04419845621.0 ppb
2021-10-04419845221.5 ppb
2021-10-04419843714.0 ppb
2021-10-05419844717.9 ppb
2021-10-0541984724.76 ppb
2021-10-05419847810.4 ppb
2021-10-0541984755.39 ppb
2021-10-05419846914.7 ppb
2022-01-0342277878.81 ppb
2022-01-0342278124.04 ppb
2022-01-0342278067.31 ppb
2022-01-0342277885.40 ppb
2022-01-0342278086.16 ppb
2022-01-03422780410.6 ppb
2022-01-0342277976.01 ppb
2022-01-0342277906.35 ppb
2022-01-0342277947.75 ppb
2022-01-03422779912.4 ppb
2022-01-0442277917.53 ppb
2022-01-0442278155.60 ppb
2022-04-04427156112.2 ppb
2022-04-0442715689.07 ppb
2022-04-04427155714.4 ppb
2022-04-04427154110.9 ppb
2022-04-04427154310.2 ppb
2022-04-0442715649.42 ppb
2022-04-04427154612.2 ppb
2022-04-04427155415.5 ppb
2022-04-04427155210.2 ppb
2022-04-0442715499.13 ppb
2022-04-0442715429.45 ppb
2022-04-0442715657.92 ppb
2022-07-0543221528.71 ppb
2022-07-0543221519.47 ppb
2022-07-0543221598.25 ppb
2022-07-05432215612.6 ppb
2022-07-05432215010.6 ppb
2022-07-0543221587.17 ppb
2022-07-05432215712.9 ppb
2022-07-0543221558.67 ppb
2022-07-0643221742.94 ppb
2022-07-0643221619.45 ppb
2022-07-0643221766.47 ppb
2022-07-0643221549.91 ppb
2022-07-06432215312.1 ppb
2022-07-0643221753.63 ppb
2022-07-0643221607.25 ppb
2022-09-2343684700.610 ppb
2022-10-03437061923.4 ppb
2022-10-03437061615.0 ppb
2022-10-03437061820.3 ppb
2022-10-03437061715.5 ppb
2022-10-03437062013.0 ppb
2022-10-03437062213.3 ppb
2022-10-03437061315.9 ppb
2022-10-03437061221.9 ppb
2022-10-03437061414.1 ppb
2022-10-03437062117.1 ppb
2022-10-04437061519.2 ppb
2022-10-04437062314.9 ppb
2022-10-1143633642.68 ppb
2023-01-0344153287.78 ppb
2023-01-0344153267.53 ppb
2023-01-0344153198.18 ppb
2023-01-0343992147.78 ppb
2023-01-0343992138.25 ppb
2023-01-0343992167.64 ppb
2023-01-03441533513.3 ppb
2023-01-0344153298.25 ppb
2023-01-0343992098.40 ppb
2023-01-0344153237.64 ppb
2023-01-03441533310.5 ppb
2023-01-0344153346.76 ppb
2023-01-0344153207.23 ppb
2023-01-0344153188.40 ppb
2023-01-0343992116.76 ppb
2023-01-03439921210.5 ppb
2023-01-0343992177.23 ppb
2023-01-03439921013.3 ppb
2023-01-0343992088.18 ppb
2023-01-0343992157.53 ppb
2023-01-0444153378.42 ppb
2023-01-0444153368.95 ppb
2023-01-0443992072.39 ppb
2023-01-0443992056.07 ppb
2023-01-0443992038.42 ppb
2023-01-0443992048.95 ppb
2023-01-0443992062.73 ppb
2023-04-05444424010.6 ppb
2023-04-0544442447.93 ppb
2023-04-0544442427.79 ppb
2023-04-0544442468.82 ppb
2023-04-0544442499.47 ppb
2023-04-05444424711.5 ppb
2023-04-0544442457.88 ppb
2023-04-0544442437.90 ppb
2023-04-05444423910.9 ppb
2023-04-0544442487.41 ppb
2023-04-0544442419.43 ppb
2023-04-0644441342.23 ppb
2023-04-0644441402.63 ppb
2023-04-0644441444.75 ppb
2023-04-0644441285.83 ppb
2023-06-2045429580.640 ppb
2023-07-1045059378.81 ppb
2023-07-1045059739.92 ppb
2023-07-1045059568.48 ppb
2023-07-10450597010.4 ppb
2023-07-10450594217.9 ppb
2023-07-10450598011.1 ppb
2023-07-10450596311.4 ppb
2023-07-10450594011.5 ppb
2023-07-10450598313.6 ppb
2023-07-10450597711.2 ppb
2023-07-1045059669.32 ppb
2023-07-11450596012.3 ppb
2023-07-1245429600.350 ppb
2023-07-1245429590.280 ppb
2023-10-02455639513.6 ppb
2023-10-02455639210.8 ppb
2023-10-0245563919.21 ppb
2023-10-0245563949.15 ppb
2023-10-02455639715.4 ppb
2023-10-02455639810.4 ppb
2023-10-02455638917.7 ppb
2023-10-02455639618.5 ppb
2023-10-02455639313.6 ppb
2023-10-02455640017.6 ppb
2023-10-02455639011.4 ppb
2023-10-0245563998.05 ppb