Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

City of Gonzales Water 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.

 

128

Samples

0

Samples exceeding legal limit (MCL)

92

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20184.07 ppb3216ND - 61.1 ppb
20191.83 ppb3222ND - 20.9 ppb
20200.733 ppb16160.550 ppb - 1.20 ppb
20210.609 ppb1615ND - 0.850 ppb
20225.07 ppb1611ND - 31.6 ppb
20230.543 ppb1612ND - 1.20 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
2018-02-02353719070010.390 ppb
2018-02-02353719070020.520 ppb
2018-02-02353719070030.540 ppb
2018-02-02353719070040.500 ppb
2018-02-02353719070010.390 ppb
2018-02-02353719070020.520 ppb
2018-02-02353719070030.540 ppb
2018-02-02353719070040.500 ppb
2018-05-1835393231001ND
2018-05-1835393231002ND
2018-05-1835393231003ND
2018-05-183539323100461.1 ppb
2018-05-1835393231001ND
2018-05-1835393231002ND
2018-05-1835393231003ND
2018-05-183539323100461.1 ppb
2018-08-0335408663001ND
2018-08-03354086630020.630 ppb
2018-08-03354086630030.720 ppb
2018-08-03354086630040.700 ppb
2018-08-0335408663001ND
2018-08-03354086630020.630 ppb
2018-08-03354086630030.720 ppb
2018-08-03354086630040.700 ppb
2018-11-0135428204001ND
2018-11-0135428204002ND
2018-11-0135428204003ND
2018-11-0135428204004ND
2018-11-0135428204001ND
2018-11-0135428204002ND
2018-11-0135428204003ND
2018-11-0135428204004ND
2019-02-07354471240010.550 ppb
2019-02-07354471240020.510 ppb
2019-02-07354471240030.690 ppb
2019-02-07354471240040.700 ppb
2019-02-07354471240010.550 ppb
2019-02-07354471240020.510 ppb
2019-02-07354471240030.690 ppb
2019-02-07354471240040.700 ppb
2019-05-08354682870010.360 ppb
2019-05-08354682870020.690 ppb
2019-05-083546828700320.9 ppb
2019-05-0835468287004ND
2019-05-08354682870010.360 ppb
2019-05-08354682870020.690 ppb
2019-05-083546828700320.9 ppb
2019-05-0835468287004ND
2019-08-06354887330011.70 ppb
2019-08-06354887330021.19 ppb
2019-08-06354887330031.50 ppb
2019-08-06354887330040.550 ppb
2019-08-06354887330011.70 ppb
2019-08-06354887330021.19 ppb
2019-08-06354887330031.50 ppb
2019-08-06354887330040.550 ppb
2019-11-0635511100001ND
2019-11-0635511100002ND
2019-11-0635511100003ND
2019-11-0635511100004ND
2019-11-0635511100001ND
2019-11-0635511100002ND
2019-11-0635511100003ND
2019-11-0635511100004ND
2020-02-04355293520010.660 ppb
2020-02-04355293520020.700 ppb
2020-02-04355293520030.590 ppb
2020-02-04355293520040.650 ppb
2020-05-12355504840010.740 ppb
2020-05-12355504840021.000 ppb
2020-05-12355504840031.20 ppb
2020-05-12355504840040.940 ppb
2020-08-04355692380010.630 ppb
2020-08-04355692380020.660 ppb
2020-08-04355692380030.550 ppb
2020-08-04355692380040.660 ppb
2020-11-04355905220010.600 ppb
2020-11-04355905220020.740 ppb
2020-11-04355905220030.690 ppb
2020-11-04355905220040.710 ppb
2021-02-01356100640010.550 ppb
2021-02-01356100640020.670 ppb
2021-02-01356100640030.580 ppb
2021-02-01356100640040.610 ppb
2021-05-03356316880010.790 ppb
2021-05-03356316880020.730 ppb
2021-05-03356316880030.850 ppb
2021-05-03356316880040.780 ppb
2021-08-05356539480010.500 ppb
2021-08-05356539480020.390 ppb
2021-08-05356539480030.500 ppb
2021-08-05356539480040.670 ppb
2021-11-03356764170010.760 ppb
2021-11-03356764170020.670 ppb
2021-11-03356764170030.700 ppb
2021-11-0335676417004ND
2022-02-17356983730010.650 ppb
2022-02-17356983730020.700 ppb
2022-02-1735698373003ND
2022-02-1735698373004ND
2022-05-09357174130010.900 ppb
2022-05-0935717413002ND
2022-05-0935717413003ND
2022-05-0935717413004ND
2022-08-103573907000131.6 ppb
2022-08-103573907000214.5 ppb
2022-08-103573907000316.6 ppb
2022-08-103573907000413.7 ppb
2022-11-03357577160010.790 ppb
2022-11-03357577160020.500 ppb
2022-11-03357577160030.590 ppb
2022-11-03357577160040.580 ppb
2023-02-02357767370010.450 ppb
2023-02-02357767370020.720 ppb
2023-02-02357767370030.840 ppb
2023-02-02357767370040.680 ppb
2023-05-0435797439001ND
2023-05-04357974390020.550 ppb
2023-05-04357974390030.650 ppb
2023-05-04357974390040.490 ppb
2023-08-0235817723001ND
2023-08-02358177230020.940 ppb
2023-08-02358177230031.20 ppb
2023-08-02358177230040.650 ppb
2023-11-0735840526001ND
2023-11-07358405260020.750 ppb
2023-11-07358405260030.760 ppb
2023-11-0735840526004ND