Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Wallingford 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.

 

130

Samples

11

Samples exceeding legal limit (MCL)

103

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201847.5 ppb2217ND - 103.0 ppb
201942.1 ppb2217ND - 83.3 ppb
202035.7 ppb2218ND - 65.2 ppb
202139.7 ppb2217ND - 94.7 ppb
202238.7 ppb2118ND - 67.5 ppb
202345.0 ppb2117ND - 94.6 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
2018-03-05BZ9817337.6 ppb
2018-03-05BZ9817152.4 ppb
2018-03-05BZ9817042.5 ppb
2018-03-05BZ9817246.0 ppb
2018-03-05BZ98169ND
2018-04-17CA21065ND
2018-06-07CA6606154.0 ppb
2018-06-07CA6606279.9 ppb
2018-06-07CA6606364.4 ppb
2018-06-07CA6606473.5 ppb
2018-06-28CA8040729.3 ppb
2018-07-17CA91980ND
2018-08-14CB11135ND
2018-09-13CB3062769.7 ppb
2018-09-13CB3062892.3 ppb
2018-09-13CB3062987.1 ppb
2018-09-13CB30630103.0 ppb
2018-10-11CB69933ND
2018-12-13CC1358438.8 ppb
2018-12-13CC1358562.7 ppb
2018-12-13CC1358650.6 ppb
2018-12-13CC1358761.7 ppb
2019-02-21CC55842-02ND
2019-03-06CC62592-0213.6 ppb
2019-03-06CC62591-02ND
2019-03-14CC6779332.3 ppb
2019-03-14CC6779648.3 ppb
2019-03-14CC6779442.5 ppb
2019-03-14CC6779552.4 ppb
2019-04-08CC90384ND
2019-06-06CD2858858.4 ppb
2019-06-06CD2858974.9 ppb
2019-06-06CD2859072.8 ppb
2019-06-06CD2859180.8 ppb
2019-07-08CD51593ND
2019-09-123389-177.3 ppb
2019-09-123389-276.8 ppb
2019-09-123389-370.3 ppb
2019-09-123389-483.3 ppb
2019-10-10CE30938-VOCND
2019-12-053412-129.8 ppb
2019-12-053412-234.8 ppb
2019-12-053412-335.5 ppb
2019-12-053412-442.5 ppb
2020-02-03CF2515610.4 ppb
2020-02-05CF27861ND
2020-03-043443-129.6 ppb
2020-03-043443-247.7 ppb
2020-03-043443-340.2 ppb
2020-03-043443-445.7 ppb
2020-03-11CF48935ND
2020-04-08CF71118ND
2020-06-033481-152.4 ppb
2020-06-033481-260.7 ppb
2020-06-033481-358.7 ppb
2020-06-033481-465.2 ppb
2020-08-12CG530272.86 ppb
2020-09-023513-151.7 ppb
2020-09-023513-256.5 ppb
2020-09-023513-353.0 ppb
2020-09-023513-463.7 ppb
2020-10-07CG95538ND
2020-12-023544-132.1 ppb
2020-12-023544-234.2 ppb
2020-12-023544-343.5 ppb
2020-12-023544-437.3 ppb
2021-02-03CH55990-VOCND
2021-03-03CH7131525.9 ppb
2021-03-03CH7131644.2 ppb
2021-03-03CH7131729.8 ppb
2021-03-03CH7131839.9 ppb
2021-03-10CH75493ND
2021-04-07CH940070.0132 ppb
2021-04-07CH94005ND
2021-06-09CI5194845.9 ppb
2021-06-09CI5194960.1 ppb
2021-06-09CI5195056.7 ppb
2021-06-09CI5195155.5 ppb
2021-09-01CJ1767570.9 ppb
2021-09-01CJ1767680.8 ppb
2021-09-01CJ1767781.8 ppb
2021-09-01CJ1767894.7 ppb
2021-09-15CJ30037ND
2021-10-06CJ50288ND
2021-12-08CJ9358235.3 ppb
2021-12-08CJ9358349.5 ppb
2021-12-08CJ9358450.4 ppb
2021-12-08CJ9358552.5 ppb
2022-02-07CK32469-VOC13.8 ppb
2022-03-02CK7726927.3 ppb
2022-03-02CK7727036.7 ppb
2022-03-02CK7727135.3 ppb
2022-03-02CK7727228.7 ppb
2022-03-09CK82546ND
2022-04-06CL02035-VOC0.620 ppb
2022-06-09CL5304255.0 ppb
2022-06-09CL5304365.5 ppb
2022-06-09CL5304465.4 ppb
2022-06-09CL5304559.0 ppb
2022-08-10CM01614ND
2022-09-01CM2068245.4 ppb
2022-09-01CM2068367.5 ppb
2022-09-01CM2068454.9 ppb
2022-09-01CM2068563.0 ppb
2022-11-16CM86907ND
2022-12-08CN0037840.0 ppb
2022-12-08CN0037947.6 ppb
2022-12-08CN0038051.8 ppb
2022-12-08CN0038154.7 ppb
2023-01-11CN21046ND
2023-02-06CN3638313.1 ppb
2023-03-01CN5158329.0 ppb
2023-03-01CN5158450.3 ppb
2023-03-01CN5158545.1 ppb
2023-03-01CN5158646.1 ppb
2023-04-12CN81747ND
2023-06-09CO2419251.6 ppb
2023-06-09CO2419366.5 ppb
2023-06-09CO2419443.4 ppb
2023-06-09CO2419564.0 ppb
2023-07-12CO49576ND
2023-09-07C09260288.6 ppb
2023-09-07CO9260168.8 ppb
2023-09-07CO9260387.8 ppb
2023-09-07CO9260494.6 ppb
2023-10-26CP34585ND
2023-12-14CP6870141.1 ppb
2023-12-14CP6870250.5 ppb
2023-12-14CP6870352.4 ppb
2023-12-14CP6870651.4 ppb