Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

CTWC - Shoreline Region-Guilford System

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.

 

101

Samples

1

Samples exceeding legal limit (MCL)

98

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201824.0 ppb2118ND - 62.9 ppb
201924.3 ppb16169.10 ppb - 35.5 ppb
202029.3 ppb161612.0 ppb - 43.8 ppb
202136.8 ppb161614.5 ppb - 82.8 ppb
202228.8 ppb161615.4 ppb - 43.3 ppb
202337.8 ppb161613.3 ppb - 67.2 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
2018-03-15CA03073TTHM21.3 ppb
2018-03-15CA03074TTHM15.9 ppb
2018-03-15CA03075TTHM23.6 ppb
2018-03-15CA03076TTHM24.7 ppb
2018-06-26CA80045TTHM44.6 ppb
2018-06-26CA80046TTHM40.5 ppb
2018-06-26CA80047TTHM33.7 ppb
2018-06-26CA80048TTHM27.5 ppb
2018-09-12DBP 20050504236.7 ppb
2018-09-12DBP 20050504362.9 ppb
2018-09-12DBP 20050504454.5 ppb
2018-09-12DBP 20050504762.2 ppb
2018-09-13VOC1 200505275ND
2018-09-13VOC1 200505276ND
2018-09-13VOC1 200505266ND
2018-09-19VOC1 2005061163.90 ppb
2018-09-20VOC1 2005063240.600 ppb
2018-12-17DBP 20051623511.8 ppb
2018-12-17DBP 2005162378.90 ppb
2018-12-17DBP 20051623814.8 ppb
2018-12-17DBP 20051623916.9 ppb
2019-03-11DBP 2005241509.10 ppb
2019-03-11DBP 20052415112.9 ppb
2019-03-11DBP 20052415217.2 ppb
2019-03-11DBP 20052415418.2 ppb
2019-06-14DBP 20053667217.9 ppb
2019-06-14DBP 20053667423.4 ppb
2019-06-14DBP 20053668027.7 ppb
2019-06-14DBP 20053668227.4 ppb
2019-09-17DBP 20054947828.6 ppb
2019-09-17DBP 20054947932.7 ppb
2019-09-17DBP 20054948034.8 ppb
2019-09-17DBP 20054948135.5 ppb
2019-12-10DBP 20055964216.1 ppb
2019-12-10DBP 20055964324.6 ppb
2019-12-10DBP 20055964429.1 ppb
2019-12-10DBP 20055964533.5 ppb
2020-03-03DBP 20056799816.5 ppb
2020-03-05DBP 20056857412.0 ppb
2020-03-05DBP 20056857520.3 ppb
2020-03-05DBP 20056857620.9 ppb
2020-06-16DBP 20057954328.8 ppb
2020-06-16DBP 20057954538.0 ppb
2020-06-16DBP 20057954643.8 ppb
2020-06-16DBP 20057954739.0 ppb
2020-09-17DBP 20059105121.6 ppb
2020-09-17DBP 20059105232.6 ppb
2020-09-17DBP 20059105339.5 ppb
2020-09-17DBP 20059105442.5 ppb
2020-12-22DBP 20060203018.3 ppb
2020-12-22DBP 20060203133.9 ppb
2020-12-22DBP 20060203230.9 ppb
2020-12-22DBP 20060203329.6 ppb
2021-03-15DBP 20060984215.6 ppb
2021-03-15DBP 20060984320.7 ppb
2021-03-15DBP 20060984423.1 ppb
2021-03-15DBP 20060984523.9 ppb
2021-06-02DBP 20061926330.1 ppb
2021-06-02DBP 20061926438.7 ppb
2021-06-02DBP 20061926541.2 ppb
2021-06-02DBP 20061926643.1 ppb
2021-09-14300059734 30005973953.0 ppb
2021-09-14300059735 30005974152.7 ppb
2021-09-14300059736 30005974377.9 ppb
2021-09-14300059737 30005974582.8 ppb
2021-12-09D300117672 30011767714.5 ppb
2021-12-09D300117673 30011767919.6 ppb
2021-12-09D300117674 30011768127.0 ppb
2021-12-09D300117675 30011768325.6 ppb
2022-03-09CK8351915.4 ppb
2022-03-09CK8352017.2 ppb
2022-03-09CK8352120.0 ppb
2022-03-25CK9523021.9 ppb
2022-06-16CL5884421.3 ppb
2022-06-16CL5884537.3 ppb
2022-06-16CL5884630.3 ppb
2022-06-16CL5884739.8 ppb
2022-09-13CM3071417.3 ppb
2022-09-13CM3069539.2 ppb
2022-09-13CM3069627.4 ppb
2022-09-13CM3069740.1 ppb
2022-12-01CM9758724.5 ppb
2022-12-01CM9758843.3 ppb
2022-12-01CM9758930.1 ppb
2022-12-01CM9759035.4 ppb
2023-03-22CN6648713.3 ppb
2023-03-22CN6648823.4 ppb
2023-03-22CN6648916.9 ppb
2023-03-22CN6649022.1 ppb
2023-06-15CO3199622.8 ppb
2023-06-15CO3199738.9 ppb
2023-06-15CO3199833.2 ppb
2023-06-15CO3199935.0 ppb
2023-09-05CO9068351.4 ppb
2023-09-05CO9068461.1 ppb
2023-09-05CO9068552.7 ppb
2023-09-05CO9068667.2 ppb
2023-12-07CP6507827.0 ppb
2023-12-07CP6507958.1 ppb
2023-12-07CP6508035.7 ppb
2023-12-07CP6508145.7 ppb