Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

San Martin County Water District

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.

 

12

Samples

0

Samples exceeding legal limit (MCL)

4

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20180.790 ppb220.630 ppb - 0.950 ppb
2019ND20ND
2020ND20ND
2021ND20ND
2022ND20ND
20230.905 ppb220.710 ppb - 1.10 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
2018-06-14CA4300542_DST_901-2018061410020.950 ppb
2018-06-14CA4300542_DST_900-2018061410250.630 ppb
2019-06-25CA4300542_DST_901-201906251329ND
2019-06-25CA4300542_DST_900-201906251346ND
2020-06-10CA4300542_DST_901-202006101152ND
2020-06-10CA4300542_DST_900-202006101129ND
2021-06-09CA4300542_DST_901-202106091330ND
2021-06-09CA4300542_DST_900-202106091345ND
2022-06-20CA4300542_DST_900-202206201407ND
2022-06-20CA4300542_DST_901-202206201324ND
2023-06-12CA4300542_DST_900-2023061213490.710 ppb
2023-06-12CA4300542_DST_901-2023061213101.10 ppb