Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

Castle Mountain Creeks Owners Association

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.

 

25

Samples

2

Samples exceeding legal limit (MCL)

13

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201819.7 ppb42ND - 58.5 ppb
20198.17 ppb42ND - 28.0 ppb
2020ND40ND
202118.0 ppb42ND - 44.7 ppb
202228.2 ppb53ND - 91.5 ppb
202365.9 ppb4443.8 ppb - 80.8 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
2018-01-16D180201358.5 ppb
2018-03-06D180951120.1 ppb
2018-07-03D1830967ND
2018-10-11D1850737ND
2019-01-10D190150928.0 ppb
2019-04-09D19157974.69 ppb
2019-07-15D1934072ND
2019-10-10D1951258ND
2020-02-06D2005375ND
2020-05-13D2021732ND
2020-08-24D2041257ND
2020-12-08D2061675ND
2021-01-08D2101071ND
2021-04-21D211820427.2 ppb
2021-07-15D2135855ND
2021-10-26D215758444.7 ppb
2022-03-07D2210665ND
2022-04-06D221600237.9 ppb
2022-09-21D224718891.5 ppb
2022-12-22V2262581ND
2022-12-22D226258311.8 ppb
2023-03-19D2305149-0143.8 ppb
2023-06-21D2312493-0174.3 ppb
2023-09-24D2320726-0180.8 ppb
2023-12-14V2326735-0164.5 ppb