Total trihalomethanes (TTHMs)
Regional Water Authority
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.
Samples
Samples exceeding legal limit (MCL)
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2018 | 60.7 ppb | 48 | 48 | 40.8 ppb - 81.9 ppb |
| 2019 | 44.5 ppb | 48 | 48 | 26.1 ppb - 72.1 ppb |
| 2020 | 41.0 ppb | 50 | 50 | 7.10 ppb - 70.5 ppb |
| 2021 | 38.0 ppb | 49 | 49 | 7.10 ppb - 79.7 ppb |
| 2022 | 44.0 ppb | 49 | 49 | 3.60 ppb - 70.7 ppb |
| 2023 | 36.2 ppb | 49 | 49 | 15.2 ppb - 82.6 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 |
|---|---|---|
| 2018-03-06 | DBP 200489268 | 48.3 ppb |
| 2018-03-06 | DBP 200489275 | 49.7 ppb |
| 2018-03-06 | DBP 200489287 | 60.9 ppb |
| 2018-03-07 | DBP 200489537 | 59.4 ppb |
| 2018-03-07 | DBP 200489538 | 59.5 ppb |
| 2018-03-07 | DBP 200489539 | 81.3 ppb |
| 2018-03-07 | DBP 200489540 | 64.9 ppb |
| 2018-03-07 | DBP 200489541 | 49.1 ppb |
| 2018-03-08 | DBP 200489565 | 43.3 ppb |
| 2018-03-09 | DBP 200489701 | 75.7 ppb |
| 2018-03-09 | DBP 200489702 | 79.3 ppb |
| 2018-03-09 | DBP 200489703 | 40.8 ppb |
| 2018-06-05 | DBP 200495984 | 51.4 ppb |
| 2018-06-05 | DBP 200495989 | 54.7 ppb |
| 2018-06-05 | DBP 200496002 | 67.7 ppb |
| 2018-06-06 | DBP 200496235 | 62.0 ppb |
| 2018-06-07 | DBP 200496375 | 42.3 ppb |
| 2018-06-07 | DBP 200496376 | 57.6 ppb |
| 2018-06-07 | DBP 200496417 | 54.0 ppb |
| 2018-06-08 | DBP 200496507 | 72.1 ppb |
| 2018-06-08 | DBP 200496508 | 46.8 ppb |
| 2018-06-08 | DBP 200496509 | 69.3 ppb |
| 2018-06-08 | DBP 200496510 | 69.1 ppb |
| 2018-06-08 | DBP 200496511 | 50.5 ppb |
| 2018-09-04 | DBP 200503732 | 62.8 ppb |
| 2018-09-04 | DBP 200503737 | 64.2 ppb |
| 2018-09-04 | DBP 200503842 | 70.2 ppb |
| 2018-09-04 | DBP 200503912 | 81.9 ppb |
| 2018-09-04 | DBP 200503913 | 81.8 ppb |
| 2018-09-04 | DBP 200503914 | 66.1 ppb |
| 2018-09-05 | DBP 200503981 | 77.6 ppb |
| 2018-09-05 | DBP 200504086 | 52.5 ppb |
| 2018-09-05 | DBP 200504087 | 61.8 ppb |
| 2018-09-06 | DBP 200504185 | 62.8 ppb |
| 2018-09-06 | DBP 200504211 | 68.6 ppb |
| 2018-09-07 | DBP 200504441 | 57.7 ppb |
| 2018-12-03 | DBP 200514372 | 42.6 ppb |
| 2018-12-03 | DBP 200514406 | 52.1 ppb |
| 2018-12-04 | DBP 200514447 | 51.5 ppb |
| 2018-12-04 | DBP 200514452 | 60.3 ppb |
| 2018-12-04 | DBP 200514625 | 74.1 ppb |
| 2018-12-04 | DBP 200514626 | 78.8 ppb |
| 2018-12-04 | DBP 200514627 | 59.1 ppb |
| 2018-12-04 | DBP 200514628 | 48.0 ppb |
| 2018-12-04 | DBP 200514629 | 62.6 ppb |
| 2018-12-05 | DBP 200514952 | 60.8 ppb |
| 2018-12-06 | DBP 200515069 | 49.5 ppb |
| 2018-12-06 | DBP 200515070 | 58.5 ppb |
| 2019-03-04 | DBP 200523215 | 27.0 ppb |
| 2019-03-04 | DBP 200523217 | 33.8 ppb |
| 2019-03-05 | DBP 200523262 | 28.8 ppb |
| 2019-03-05 | DBP 200523269 | 32.7 ppb |
| 2019-03-05 | DBP 200523456 | 33.2 ppb |
| 2019-03-05 | DBP 200523457 | 45.1 ppb |
| 2019-03-05 | DBP 200523458 | 35.4 ppb |
| 2019-03-05 | DBP 200523459 | 32.5 ppb |
| 2019-03-05 | DBP 200523463 | 29.3 ppb |
| 2019-03-07 | DBP 200523884 | 29.5 ppb |
| 2019-03-08 | DBP 200524000 | 26.1 ppb |
| 2019-03-08 | DBP 200524002 | 34.0 ppb |
| 2019-06-03 | DBP 200534373 | 45.5 ppb |
| 2019-06-03 | DBP 200534414 | 54.5 ppb |
| 2019-06-04 | DBP 200534491 | 43.5 ppb |
| 2019-06-04 | DBP 200534496 | 45.7 ppb |
| 2019-06-04 | DBP 200534600 | 41.6 ppb |
| 2019-06-04 | DBP 200534725 | 57.0 ppb |
| 2019-06-04 | DBP 200534727 | 48.9 ppb |
| 2019-06-04 | DBP 200534729 | 56.8 ppb |
| 2019-06-05 | DBP 200535039 | 60.4 ppb |
| 2019-06-05 | DBP 200535041 | 44.6 ppb |
| 2019-06-06 | DBP 200535197 | 46.6 ppb |
| 2019-06-07 | DBP 200535357 | 52.4 ppb |
| 2019-09-03 | DBP 200546988 | 51.1 ppb |
| 2019-09-03 | DBP 200546993 | 59.2 ppb |
| 2019-09-04 | DBP 200547400 | 51.3 ppb |
| 2019-09-04 | DBP 200547402 | 59.5 ppb |
| 2019-09-04 | DBP 200547403 | 59.7 ppb |
| 2019-09-04 | DBP 200547404 | 54.6 ppb |
| 2019-09-04 | DBP 200547405 | 47.6 ppb |
| 2019-09-05 | DBP 200547460 | 72.1 ppb |
| 2019-09-05 | DBP 200547667 | 70.5 ppb |
| 2019-09-06 | DBP 200547826 | 54.7 ppb |
| 2019-09-06 | DBP 200547827 | 64.7 ppb |
| 2019-09-06 | DBP 200547828 | 53.4 ppb |
| 2019-12-02 | DBP 200558405 | 43.1 ppb |
| 2019-12-02 | DBP 200558406 | 37.9 ppb |
| 2019-12-02 | DBP 200558407 | 46.1 ppb |
| 2019-12-03 | DBP 200558454 | 33.8 ppb |
| 2019-12-03 | DBP 200558459 | 38.4 ppb |
| 2019-12-03 | DBP 200558612 | 38.9 ppb |
| 2019-12-04 | DBP 200558916 | 35.7 ppb |
| 2019-12-04 | DBP 200558917 | 39.2 ppb |
| 2019-12-04 | DBP 200558919 | 32.8 ppb |
| 2019-12-05 | DBP 200559073 | 41.5 ppb |
| 2019-12-05 | DBP 200559098 | 30.7 ppb |
| 2019-12-06 | DBP 200559195 | 36.2 ppb |
| 2020-03-02 | DBP 200567713 | 36.4 ppb |
| 2020-03-02 | DBP 200567714 | 54.1 ppb |
| 2020-03-02 | DBP 200567715 | 44.0 ppb |
| 2020-03-02 | DBP 200567718 | 34.2 ppb |
| 2020-03-03 | DBP 200567780 | 35.3 ppb |
| 2020-03-03 | DBP 200567787 | 41.4 ppb |
| 2020-03-03 | DBP 200567920 | 38.2 ppb |
| 2020-03-03 | DBP 200567921 | 33.7 ppb |
| 2020-03-04 | DBP 200568177 | 37.7 ppb |
| 2020-03-04 | DBP 200568178 | 32.8 ppb |
| 2020-03-05 | DBP 200568285 | 7.10 ppb |
| 2020-03-05 | DBP 200568384 | 28.3 ppb |
| 2020-03-12 | DBP 200569164 | 33.5 ppb |
| 2020-06-01 | DBP 200577264 | 39.4 ppb |
| 2020-06-01 | DBP 200577265 | 50.6 ppb |
| 2020-06-01 | DBP 200577266 | 45.8 ppb |
| 2020-06-02 | DBP 200577318 | 40.0 ppb |
| 2020-06-02 | DBP 200577327 | 30.9 ppb |
| 2020-06-02 | DBP 200577399 | 45.3 ppb |
| 2020-06-02 | DBP 200577401 | 36.1 ppb |
| 2020-06-03 | DBP 200577719 | 41.8 ppb |
| 2020-06-03 | DBP 200577721 | 43.7 ppb |
| 2020-06-04 | DBP 200577954 | 35.3 ppb |
| 2020-06-04 | DBP 200577955 | 36.7 ppb |
| 2020-06-05 | DBP 200578077 | 35.4 ppb |
| 2020-09-08 | DBP 200589109 | 69.1 ppb |
| 2020-09-08 | DBP 200589118 | 58.9 ppb |
| 2020-09-08 | DBP 200589252 | 70.5 ppb |
| 2020-09-08 | DBP 200589253 | 64.1 ppb |
| 2020-09-08 | DBP 200589254 | 65.4 ppb |
| 2020-09-09 | DBP 200589560 | 48.8 ppb |
| 2020-09-09 | DBP 200589561 | 56.1 ppb |
| 2020-09-10 | DBP 200589797 | 52.3 ppb |
| 2020-09-10 | DBP 200589799 | 42.8 ppb |
| 2020-09-10 | DBP 200589803 | 63.8 ppb |
| 2020-09-10 | DBP 200589806 | 46.3 ppb |
| 2020-09-11 | DBP 200589868 | 55.6 ppb |
| 2020-12-07 | DBP 200600136 | 38.9 ppb |
| 2020-12-07 | DBP 200600137 | 36.7 ppb |
| 2020-12-08 | DBP 200600326 | 35.0 ppb |
| 2020-12-08 | DBP 200600407 | 32.4 ppb |
| 2020-12-08 | DBP 200600408 | 35.7 ppb |
| 2020-12-09 | DBP 200600562 | 29.6 ppb |
| 2020-12-09 | DBP 200600607 | 22.7 ppb |
| 2020-12-09 | DBP 200600653 | 33.9 ppb |
| 2020-12-09 | DBP 200600656 | 38.1 ppb |
| 2020-12-10 | DBP 200600882 | 35.0 ppb |
| 2020-12-10 | DBP 200600884 | 24.1 ppb |
| 2020-12-10 | DBP 200600884B | 24.1 ppb |
| 2020-12-11 | DBP 200600954 | 31.8 ppb |
| 2021-03-08 | DBP 200608809 | 26.4 ppb |
| 2021-03-08 | DBP 200608835 | 24.6 ppb |
| 2021-03-08 | DBP 200608836 | 29.0 ppb |
| 2021-03-08 | DBP 200608837 | 24.3 ppb |
| 2021-03-09 | DBP 200608914 | 23.9 ppb |
| 2021-03-09 | DBP 200609089 | 32.1 ppb |
| 2021-03-09 | DBP 200609090 | 21.3 ppb |
| 2021-03-09 | DBP 200609093 | 25.8 ppb |
| 2021-03-10 | DBP 200609251 | 23.5 ppb |
| 2021-03-10 | DBP 200609252 | 21.6 ppb |
| 2021-03-11 | DBP 200609420 | 7.10 ppb |
| 2021-03-11 | DBP 200609512 | 27.0 ppb |
| 2021-03-12 | DBP 200609584 | 29.0 ppb |
| 2021-06-07 | DBP 200619680 | 38.8 ppb |
| 2021-06-07 | DBP 200619678 | 44.1 ppb |
| 2021-06-07 | DBP 200619679 | 49.6 ppb |
| 2021-06-08 | DBP 200619800 | 40.9 ppb |
| 2021-06-08 | DBP 200619802 | 43.0 ppb |
| 2021-06-08 | DBP 200619920 | 49.2 ppb |
| 2021-06-08 | DBP 200619921 | 35.3 ppb |
| 2021-06-08 | DBP 200619922 | 31.1 ppb |
| 2021-06-09 | DBP 200620173 | 39.7 ppb |
| 2021-06-10 | DBP 200620493 | 31.8 ppb |
| 2021-06-10 | DBP 200620495 | 26.8 ppb |
| 2021-06-11 | DBP 200620583 | 28.9 ppb |
| 2021-09-13 | 300057530 300057532 | 55.6 ppb |
| 2021-09-13 | 300057533 300057535 | 68.3 ppb |
| 2021-09-13 | 300057536 300057538 | 79.7 ppb |
| 2021-09-14 | 300058253 300058257 | 51.6 ppb |
| 2021-09-14 | 300058258 300058262 | 65.0 ppb |
| 2021-09-14 | 300059322 300059326 | 56.7 ppb |
| 2021-09-14 | 300059327 300059329 | 46.8 ppb |
| 2021-09-14 | 300059398 300059400 | 39.1 ppb |
| 2021-09-15 | 300060630 300060632 | 57.8 ppb |
| 2021-09-16 | 300061467 300061469 | 52.0 ppb |
| 2021-09-16 | 300061470 300061472 | 45.9 ppb |
| 2021-09-17 | 300062097 300062099 | 53.8 ppb |
| 2021-12-13 | D300118224 300118228 | 23.5 ppb |
| 2021-12-13 | D300118229 300118231 | 34.8 ppb |
| 2021-12-13 | D300117139 300117141 | 35.4 ppb |
| 2021-12-13 | D300117142 300117144 | 39.0 ppb |
| 2021-12-13 | D300117145 300117147 | 35.2 ppb |
| 2021-12-13 | D300117148 300117150 | 42.2 ppb |
| 2021-12-14 | D300117272 300117276 | 32.1 ppb |
| 2021-12-14 | D300117277 300117281 | 39.5 ppb |
| 2021-12-15 | D300119211 300119213 | 26.7 ppb |
| 2021-12-16 | D300120051 300120053 | 37.3 ppb |
| 2021-12-16 | D300120054 300120056 | 33.6 ppb |
| 2021-12-17 | D300120678 300120680 | 35.1 ppb |
| 2022-03-07 | D300153474 300153476 | 36.7 ppb |
| 2022-03-07 | D300153477 300153479 | 43.4 ppb |
| 2022-03-07 | D300153480 300153482 | 34.5 ppb |
| 2022-03-08 | D300153988 300153992 | 33.9 ppb |
| 2022-03-08 | D300153993 300153997 | 39.2 ppb |
| 2022-03-08 | D300154252 300154256 | 31.6 ppb |
| 2022-03-08 | D300154257 300154259 | 33.6 ppb |
| 2022-03-08 | D300154260 300154262 | 30.3 ppb |
| 2022-03-09 | D300155008 300155010 | 29.5 ppb |
| 2022-03-10 | D300155239 300155243 | 3.60 ppb |
| 2022-03-10 | D300155826 300155829 | 36.3 ppb |
| 2022-03-10 | D300155831 300155834 | 44.7 ppb |
| 2022-03-11 | D300156650 300156652 | 32.2 ppb |
| 2022-06-06 | D300193482 300193486 | 49.4 ppb |
| 2022-06-06 | D300193487 300193490 | 56.7 ppb |
| 2022-06-06 | D300193491 300193494 | 66.2 ppb |
| 2022-06-06 | D300193495 300193498 | 47.0 ppb |
| 2022-06-07 | D300194474 300194478 | 55.5 ppb |
| 2022-06-07 | D300194485 300194488 | 38.4 ppb |
| 2022-06-07 | D300194421 300194425 | 51.4 ppb |
| 2022-06-08 | D300194960 300194963 | 46.8 ppb |
| 2022-06-08 | D300196206 300196209 | 47.5 ppb |
| 2022-06-08 | D300196210 300196213 | 70.7 ppb |
| 2022-06-08 | D300196214 300196217 | 64.3 ppb |
| 2022-06-10 | D300196552 300196555 | 50.5 ppb |
| 2022-09-12 | D300242309 300242312 | 67.6 ppb |
| 2022-09-12 | D300242313 300242316 | 53.7 ppb |
| 2022-09-13 | D300242867 300242871 | 53.9 ppb |
| 2022-09-13 | D300242872 300242876 | 54.2 ppb |
| 2022-09-13 | D300243354 300243358 | 58.2 ppb |
| 2022-09-13 | D300243359 300243362 | 44.7 ppb |
| 2022-09-14 | D300243943 300243946 | 53.6 ppb |
| 2022-09-14 | D300243947 300243950 | 67.9 ppb |
| 2022-09-14 | D300243951 300243954 | 53.3 ppb |
| 2022-09-15 | D300244400 300244403 | 35.1 ppb |
| 2022-09-15 | D300244404 300244407 | 35.5 ppb |
| 2022-09-15 | D300245400 300245403 | 51.0 ppb |
| 2022-12-05 | D300280513 300280516 | 35.1 ppb |
| 2022-12-05 | D300280517 300280520 | 49.4 ppb |
| 2022-12-05 | D300280521 300280524 | 43.0 ppb |
| 2022-12-06 | D300281387 300281391 | 40.4 ppb |
| 2022-12-06 | D300281392 300281395 | 46.7 ppb |
| 2022-12-06 | D300281396 300281399 | 29.9 ppb |
| 2022-12-07 | D300282133 300282137 | 33.9 ppb |
| 2022-12-07 | D300282138 300282142 | 38.8 ppb |
| 2022-12-07 | D300282730 300282733 | 45.6 ppb |
| 2022-12-08 | D300283547 300283550 | 28.2 ppb |
| 2022-12-08 | D300283566 300283569 | 31.7 ppb |
| 2022-12-09 | D300284348 300284351 | 29.6 ppb |
| 2023-03-06 | D300316509 300316512 | 26.8 ppb |
| 2023-03-06 | D300316513 300316516 | 33.5 ppb |
| 2023-03-06 | D300316517 300316520 | 23.3 ppb |
| 2023-03-07 | D300317097 300317101 | 22.3 ppb |
| 2023-03-07 | D300317102 300317106 | 23.7 ppb |
| 2023-03-07 | D300317505 300317509 | 24.4 ppb |
| 2023-03-07 | D300317510 300317513 | 24.3 ppb |
| 2023-03-07 | D300317514 300317517 | 19.9 ppb |
| 2023-03-08 | D300318389 300318392 | 20.1 ppb |
| 2023-03-08 | D300318393 300318396 | 22.6 ppb |
| 2023-03-09 | D300319243 300319246 | 31.2 ppb |
| 2023-03-10 | D300319398 300319401 | 34.8 ppb |
| 2023-06-05 | D300358943 300358946 | 28.9 ppb |
| 2023-06-05 | D300358947 300358950 | 37.5 ppb |
| 2023-06-05 | D300358951 300358954 | 29.8 ppb |
| 2023-06-05 | D300358955 300358958 | 28.9 ppb |
| 2023-06-06 | D300358988 300358992 | 26.2 ppb |
| 2023-06-06 | D300358993 300358997 | 35.1 ppb |
| 2023-06-06 | D300359847 300359851 | 64.8 ppb |
| 2023-06-06 | D300359852 300359855 | 52.5 ppb |
| 2023-06-07 | D300360865 300360868 | 37.3 ppb |
| 2023-06-08 | D300361983 300361986 | 32.4 ppb |
| 2023-06-08 | D300361987 300361990 | 40.7 ppb |
| 2023-06-09 | D300362721 300362724 | 34.8 ppb |
| 2023-06-28 | D300372809 300373415 | 36.7 ppb |
| 2023-09-11 | D300412854 300412857 | 68.9 ppb |
| 2023-09-11 | D300412858 300412861 | 43.0 ppb |
| 2023-09-12 | D300413093 300413097 | 45.0 ppb |
| 2023-09-12 | D300413098 300413102 | 56.7 ppb |
| 2023-09-12 | D300413568 300413572 | 72.0 ppb |
| 2023-09-12 | D300413573 300413576 | 51.6 ppb |
| 2023-09-12 | D300413577 300413580 | 52.9 ppb |
| 2023-09-12 | D300413581 300413584 | 60.9 ppb |
| 2023-09-13 | D300414470 300414473 | 37.6 ppb |
| 2023-09-13 | D300414474 300414477 | 39.1 ppb |
| 2023-09-14 | D300415299 300415302 | 51.2 ppb |
| 2023-09-15 | D300416083 300416086 | 82.6 ppb |
| 2023-12-04 | D300454311 300454314 | 24.6 ppb |
| 2023-12-04 | D300454315 300454318 | 34.0 ppb |
| 2023-12-04 | D300454322 300454325 | 28.8 ppb |
| 2023-12-05 | D300454448 300454452 | 22.5 ppb |
| 2023-12-05 | D300454453 300454457 | 26.8 ppb |
| 2023-12-05 | D300454954 300454958 | 35.0 ppb |
| 2023-12-05 | D300454962 300454965 | 22.9 ppb |
| 2023-12-05 | D300454972 300454975 | 33.7 ppb |
| 2023-12-06 | D300455828 300455831 | 15.2 ppb |
| 2023-12-06 | D300455832 300455835 | 17.0 ppb |
| 2023-12-07 | D300456845 300456848 | 26.4 ppb |
| 2023-12-08 | D300457513 300457516 | 33.7 ppb |