Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

San Gabriel Valley Water Company-Montebello

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.

 

10

Samples

0

Samples exceeding legal limit (MCL)

5

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20180.455 ppb21ND - 0.910 ppb
20192.65 ppb222.30 ppb - 3.00 ppb
20200.610 ppb220.600 ppb - 0.620 ppb
2021ND20ND
20224.01 ppb268ND - 22.0 ppb
2023ND20ND

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
2018-09-12CA1910189_DST_801-201809120810ND
2018-09-12CA1910189_DST_800-2018091208210.910 ppb
2019-09-25CA1910189_DST_800-2019092509153.00 ppb
2019-09-25CA1910189_DST_801-2019092509232.30 ppb
2020-09-15CA1910189_DST_800-2020091509000.620 ppb
2020-09-15CA1910189_DST_801-2020091509200.600 ppb
2021-09-21CA1910189_DST_800-202109211420ND
2021-09-21CA1910189_DST_801-202109211411ND
2023-09-19CA1910189_DST_800-202309191242ND
2023-09-19CA1910189_DST_801-202309191225ND