Know Your Environment. Protect Your Health.

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.

Click here to read more about disinfection byproducts.

 

293

Samples

4

Samples exceeding legal limit (MCL)

293

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201860.7 ppb484840.8 ppb - 81.9 ppb
201944.5 ppb484826.1 ppb - 72.1 ppb
202041.0 ppb50507.10 ppb - 70.5 ppb
202138.0 ppb49497.10 ppb - 79.7 ppb
202244.0 ppb49493.60 ppb - 70.7 ppb
202336.2 ppb494915.2 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
2018-03-06DBP 20048926848.3 ppb
2018-03-06DBP 20048927549.7 ppb
2018-03-06DBP 20048928760.9 ppb
2018-03-07DBP 20048953759.4 ppb
2018-03-07DBP 20048953859.5 ppb
2018-03-07DBP 20048953981.3 ppb
2018-03-07DBP 20048954064.9 ppb
2018-03-07DBP 20048954149.1 ppb
2018-03-08DBP 20048956543.3 ppb
2018-03-09DBP 20048970175.7 ppb
2018-03-09DBP 20048970279.3 ppb
2018-03-09DBP 20048970340.8 ppb
2018-06-05DBP 20049598451.4 ppb
2018-06-05DBP 20049598954.7 ppb
2018-06-05DBP 20049600267.7 ppb
2018-06-06DBP 20049623562.0 ppb
2018-06-07DBP 20049637542.3 ppb
2018-06-07DBP 20049637657.6 ppb
2018-06-07DBP 20049641754.0 ppb
2018-06-08DBP 20049650772.1 ppb
2018-06-08DBP 20049650846.8 ppb
2018-06-08DBP 20049650969.3 ppb
2018-06-08DBP 20049651069.1 ppb
2018-06-08DBP 20049651150.5 ppb
2018-09-04DBP 20050373262.8 ppb
2018-09-04DBP 20050373764.2 ppb
2018-09-04DBP 20050384270.2 ppb
2018-09-04DBP 20050391281.9 ppb
2018-09-04DBP 20050391381.8 ppb
2018-09-04DBP 20050391466.1 ppb
2018-09-05DBP 20050398177.6 ppb
2018-09-05DBP 20050408652.5 ppb
2018-09-05DBP 20050408761.8 ppb
2018-09-06DBP 20050418562.8 ppb
2018-09-06DBP 20050421168.6 ppb
2018-09-07DBP 20050444157.7 ppb
2018-12-03DBP 20051437242.6 ppb
2018-12-03DBP 20051440652.1 ppb
2018-12-04DBP 20051444751.5 ppb
2018-12-04DBP 20051445260.3 ppb
2018-12-04DBP 20051462574.1 ppb
2018-12-04DBP 20051462678.8 ppb
2018-12-04DBP 20051462759.1 ppb
2018-12-04DBP 20051462848.0 ppb
2018-12-04DBP 20051462962.6 ppb
2018-12-05DBP 20051495260.8 ppb
2018-12-06DBP 20051506949.5 ppb
2018-12-06DBP 20051507058.5 ppb
2019-03-04DBP 20052321527.0 ppb
2019-03-04DBP 20052321733.8 ppb
2019-03-05DBP 20052326228.8 ppb
2019-03-05DBP 20052326932.7 ppb
2019-03-05DBP 20052345633.2 ppb
2019-03-05DBP 20052345745.1 ppb
2019-03-05DBP 20052345835.4 ppb
2019-03-05DBP 20052345932.5 ppb
2019-03-05DBP 20052346329.3 ppb
2019-03-07DBP 20052388429.5 ppb
2019-03-08DBP 20052400026.1 ppb
2019-03-08DBP 20052400234.0 ppb
2019-06-03DBP 20053437345.5 ppb
2019-06-03DBP 20053441454.5 ppb
2019-06-04DBP 20053449143.5 ppb
2019-06-04DBP 20053449645.7 ppb
2019-06-04DBP 20053460041.6 ppb
2019-06-04DBP 20053472557.0 ppb
2019-06-04DBP 20053472748.9 ppb
2019-06-04DBP 20053472956.8 ppb
2019-06-05DBP 20053503960.4 ppb
2019-06-05DBP 20053504144.6 ppb
2019-06-06DBP 20053519746.6 ppb
2019-06-07DBP 20053535752.4 ppb
2019-09-03DBP 20054698851.1 ppb
2019-09-03DBP 20054699359.2 ppb
2019-09-04DBP 20054740051.3 ppb
2019-09-04DBP 20054740259.5 ppb
2019-09-04DBP 20054740359.7 ppb
2019-09-04DBP 20054740454.6 ppb
2019-09-04DBP 20054740547.6 ppb
2019-09-05DBP 20054746072.1 ppb
2019-09-05DBP 20054766770.5 ppb
2019-09-06DBP 20054782654.7 ppb
2019-09-06DBP 20054782764.7 ppb
2019-09-06DBP 20054782853.4 ppb
2019-12-02DBP 20055840543.1 ppb
2019-12-02DBP 20055840637.9 ppb
2019-12-02DBP 20055840746.1 ppb
2019-12-03DBP 20055845433.8 ppb
2019-12-03DBP 20055845938.4 ppb
2019-12-03DBP 20055861238.9 ppb
2019-12-04DBP 20055891635.7 ppb
2019-12-04DBP 20055891739.2 ppb
2019-12-04DBP 20055891932.8 ppb
2019-12-05DBP 20055907341.5 ppb
2019-12-05DBP 20055909830.7 ppb
2019-12-06DBP 20055919536.2 ppb
2020-03-02DBP 20056771336.4 ppb
2020-03-02DBP 20056771454.1 ppb
2020-03-02DBP 20056771544.0 ppb
2020-03-02DBP 20056771834.2 ppb
2020-03-03DBP 20056778035.3 ppb
2020-03-03DBP 20056778741.4 ppb
2020-03-03DBP 20056792038.2 ppb
2020-03-03DBP 20056792133.7 ppb
2020-03-04DBP 20056817737.7 ppb
2020-03-04DBP 20056817832.8 ppb
2020-03-05DBP 2005682857.10 ppb
2020-03-05DBP 20056838428.3 ppb
2020-03-12DBP 20056916433.5 ppb
2020-06-01DBP 20057726439.4 ppb
2020-06-01DBP 20057726550.6 ppb
2020-06-01DBP 20057726645.8 ppb
2020-06-02DBP 20057731840.0 ppb
2020-06-02DBP 20057732730.9 ppb
2020-06-02DBP 20057739945.3 ppb
2020-06-02DBP 20057740136.1 ppb
2020-06-03DBP 20057771941.8 ppb
2020-06-03DBP 20057772143.7 ppb
2020-06-04DBP 20057795435.3 ppb
2020-06-04DBP 20057795536.7 ppb
2020-06-05DBP 20057807735.4 ppb
2020-09-08DBP 20058910969.1 ppb
2020-09-08DBP 20058911858.9 ppb
2020-09-08DBP 20058925270.5 ppb
2020-09-08DBP 20058925364.1 ppb
2020-09-08DBP 20058925465.4 ppb
2020-09-09DBP 20058956048.8 ppb
2020-09-09DBP 20058956156.1 ppb
2020-09-10DBP 20058979752.3 ppb
2020-09-10DBP 20058979942.8 ppb
2020-09-10DBP 20058980363.8 ppb
2020-09-10DBP 20058980646.3 ppb
2020-09-11DBP 20058986855.6 ppb
2020-12-07DBP 20060013638.9 ppb
2020-12-07DBP 20060013736.7 ppb
2020-12-08DBP 20060032635.0 ppb
2020-12-08DBP 20060040732.4 ppb
2020-12-08DBP 20060040835.7 ppb
2020-12-09DBP 20060056229.6 ppb
2020-12-09DBP 20060060722.7 ppb
2020-12-09DBP 20060065333.9 ppb
2020-12-09DBP 20060065638.1 ppb
2020-12-10DBP 20060088235.0 ppb
2020-12-10DBP 20060088424.1 ppb
2020-12-10DBP 200600884B24.1 ppb
2020-12-11DBP 20060095431.8 ppb
2021-03-08DBP 20060880926.4 ppb
2021-03-08DBP 20060883524.6 ppb
2021-03-08DBP 20060883629.0 ppb
2021-03-08DBP 20060883724.3 ppb
2021-03-09DBP 20060891423.9 ppb
2021-03-09DBP 20060908932.1 ppb
2021-03-09DBP 20060909021.3 ppb
2021-03-09DBP 20060909325.8 ppb
2021-03-10DBP 20060925123.5 ppb
2021-03-10DBP 20060925221.6 ppb
2021-03-11DBP 2006094207.10 ppb
2021-03-11DBP 20060951227.0 ppb
2021-03-12DBP 20060958429.0 ppb
2021-06-07DBP 20061968038.8 ppb
2021-06-07DBP 20061967844.1 ppb
2021-06-07DBP 20061967949.6 ppb
2021-06-08DBP 20061980040.9 ppb
2021-06-08DBP 20061980243.0 ppb
2021-06-08DBP 20061992049.2 ppb
2021-06-08DBP 20061992135.3 ppb
2021-06-08DBP 20061992231.1 ppb
2021-06-09DBP 20062017339.7 ppb
2021-06-10DBP 20062049331.8 ppb
2021-06-10DBP 20062049526.8 ppb
2021-06-11DBP 20062058328.9 ppb
2021-09-13300057530 30005753255.6 ppb
2021-09-13300057533 30005753568.3 ppb
2021-09-13300057536 30005753879.7 ppb
2021-09-14300058253 30005825751.6 ppb
2021-09-14300058258 30005826265.0 ppb
2021-09-14300059322 30005932656.7 ppb
2021-09-14300059327 30005932946.8 ppb
2021-09-14300059398 30005940039.1 ppb
2021-09-15300060630 30006063257.8 ppb
2021-09-16300061467 30006146952.0 ppb
2021-09-16300061470 30006147245.9 ppb
2021-09-17300062097 30006209953.8 ppb
2021-12-13D300118224 30011822823.5 ppb
2021-12-13D300118229 30011823134.8 ppb
2021-12-13D300117139 30011714135.4 ppb
2021-12-13D300117142 30011714439.0 ppb
2021-12-13D300117145 30011714735.2 ppb
2021-12-13D300117148 30011715042.2 ppb
2021-12-14D300117272 30011727632.1 ppb
2021-12-14D300117277 30011728139.5 ppb
2021-12-15D300119211 30011921326.7 ppb
2021-12-16D300120051 30012005337.3 ppb
2021-12-16D300120054 30012005633.6 ppb
2021-12-17D300120678 30012068035.1 ppb
2022-03-07D300153474 30015347636.7 ppb
2022-03-07D300153477 30015347943.4 ppb
2022-03-07D300153480 30015348234.5 ppb
2022-03-08D300153988 30015399233.9 ppb
2022-03-08D300153993 30015399739.2 ppb
2022-03-08D300154252 30015425631.6 ppb
2022-03-08D300154257 30015425933.6 ppb
2022-03-08D300154260 30015426230.3 ppb
2022-03-09D300155008 30015501029.5 ppb
2022-03-10D300155239 3001552433.60 ppb
2022-03-10D300155826 30015582936.3 ppb
2022-03-10D300155831 30015583444.7 ppb
2022-03-11D300156650 30015665232.2 ppb
2022-06-06D300193482 30019348649.4 ppb
2022-06-06D300193487 30019349056.7 ppb
2022-06-06D300193491 30019349466.2 ppb
2022-06-06D300193495 30019349847.0 ppb
2022-06-07D300194474 30019447855.5 ppb
2022-06-07D300194485 30019448838.4 ppb
2022-06-07D300194421 30019442551.4 ppb
2022-06-08D300194960 30019496346.8 ppb
2022-06-08D300196206 30019620947.5 ppb
2022-06-08D300196210 30019621370.7 ppb
2022-06-08D300196214 30019621764.3 ppb
2022-06-10D300196552 30019655550.5 ppb
2022-09-12D300242309 30024231267.6 ppb
2022-09-12D300242313 30024231653.7 ppb
2022-09-13D300242867 30024287153.9 ppb
2022-09-13D300242872 30024287654.2 ppb
2022-09-13D300243354 30024335858.2 ppb
2022-09-13D300243359 30024336244.7 ppb
2022-09-14D300243943 30024394653.6 ppb
2022-09-14D300243947 30024395067.9 ppb
2022-09-14D300243951 30024395453.3 ppb
2022-09-15D300244400 30024440335.1 ppb
2022-09-15D300244404 30024440735.5 ppb
2022-09-15D300245400 30024540351.0 ppb
2022-12-05D300280513 30028051635.1 ppb
2022-12-05D300280517 30028052049.4 ppb
2022-12-05D300280521 30028052443.0 ppb
2022-12-06D300281387 30028139140.4 ppb
2022-12-06D300281392 30028139546.7 ppb
2022-12-06D300281396 30028139929.9 ppb
2022-12-07D300282133 30028213733.9 ppb
2022-12-07D300282138 30028214238.8 ppb
2022-12-07D300282730 30028273345.6 ppb
2022-12-08D300283547 30028355028.2 ppb
2022-12-08D300283566 30028356931.7 ppb
2022-12-09D300284348 30028435129.6 ppb
2023-03-06D300316509 30031651226.8 ppb
2023-03-06D300316513 30031651633.5 ppb
2023-03-06D300316517 30031652023.3 ppb
2023-03-07D300317097 30031710122.3 ppb
2023-03-07D300317102 30031710623.7 ppb
2023-03-07D300317505 30031750924.4 ppb
2023-03-07D300317510 30031751324.3 ppb
2023-03-07D300317514 30031751719.9 ppb
2023-03-08D300318389 30031839220.1 ppb
2023-03-08D300318393 30031839622.6 ppb
2023-03-09D300319243 30031924631.2 ppb
2023-03-10D300319398 30031940134.8 ppb
2023-06-05D300358943 30035894628.9 ppb
2023-06-05D300358947 30035895037.5 ppb
2023-06-05D300358951 30035895429.8 ppb
2023-06-05D300358955 30035895828.9 ppb
2023-06-06D300358988 30035899226.2 ppb
2023-06-06D300358993 30035899735.1 ppb
2023-06-06D300359847 30035985164.8 ppb
2023-06-06D300359852 30035985552.5 ppb
2023-06-07D300360865 30036086837.3 ppb
2023-06-08D300361983 30036198632.4 ppb
2023-06-08D300361987 30036199040.7 ppb
2023-06-09D300362721 30036272434.8 ppb
2023-06-28D300372809 30037341536.7 ppb
2023-09-11D300412854 30041285768.9 ppb
2023-09-11D300412858 30041286143.0 ppb
2023-09-12D300413093 30041309745.0 ppb
2023-09-12D300413098 30041310256.7 ppb
2023-09-12D300413568 30041357272.0 ppb
2023-09-12D300413573 30041357651.6 ppb
2023-09-12D300413577 30041358052.9 ppb
2023-09-12D300413581 30041358460.9 ppb
2023-09-13D300414470 30041447337.6 ppb
2023-09-13D300414474 30041447739.1 ppb
2023-09-14D300415299 30041530251.2 ppb
2023-09-15D300416083 30041608682.6 ppb
2023-12-04D300454311 30045431424.6 ppb
2023-12-04D300454315 30045431834.0 ppb
2023-12-04D300454322 30045432528.8 ppb
2023-12-05D300454448 30045445222.5 ppb
2023-12-05D300454453 30045445726.8 ppb
2023-12-05D300454954 30045495835.0 ppb
2023-12-05D300454962 30045496522.9 ppb
2023-12-05D300454972 30045497533.7 ppb
2023-12-06D300455828 30045583115.2 ppb
2023-12-06D300455832 30045583517.0 ppb
2023-12-07D300456845 30045684826.4 ppb
2023-12-08D300457513 30045751633.7 ppb