Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Gig Harbor Water Department

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.

 

27

Samples

0

Samples exceeding legal limit (MCL)

17

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20180.465 ppb43ND - 1.01 ppb
20190.325 ppb145ND - 1.80 ppb
2020N/A00N/A
20210.790 ppb110.790 ppb
20222.24 ppb440.790 ppb - 3.75 ppb
20232.77 ppb441.33 ppb - 4.23 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
2018-08-081.01 ppb
2018-08-080.500 ppb
2018-08-080.350 ppb
2018-08-08ND
2019-03-21ND
2019-05-13ND
2019-05-13ND
2019-05-13ND
2019-05-13ND
2019-05-13ND
2019-08-081.13 ppb
2019-08-080.520 ppb
2019-08-081.80 ppb
2019-08-080.530 ppb
2019-08-22ND
2019-08-220.570 ppb
2019-08-22ND
2019-08-22ND
2021-08-0341593200.790 ppb
2022-08-0943386781.94 ppb
2022-08-0943386813.75 ppb
2022-08-0943386760.790 ppb
2022-08-0943386742.47 ppb
2023-08-0745057591.33 ppb
2023-08-0745057603.18 ppb
2023-08-0745057614.23 ppb
2023-08-0745057622.32 ppb