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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

CTWC - Shoreline Region-Guilford 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.

MORE ABOUT THIS CONTAMINANT

 

101

Samples

0

Samples exceeding legal limit (MCL)

98

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201435.2 ppb16168.50 ppb - 52.9 ppb
201533.4 ppb161616.4 ppb - 49.1 ppb
201626.9 ppb16167.10 ppb - 41.9 ppb
201734.6 ppb161615.0 ppb - 56.0 ppb
201824.0 ppb2118ND - 62.9 ppb
201924.3 ppb16169.10 ppb - 35.5 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

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
2014-03-213482THM15.8 ppb
2014-03-213483THM8.50 ppb
2014-03-213484THM25.1 ppb
2014-03-213485THM33.5 ppb
2014-06-188760THM45.8 ppb
2014-06-188761THM52.9 ppb
2014-06-188764THM44.2 ppb
2014-06-188765THM45.8 ppb
2014-09-15BH14101TTHM29.7 ppb
2014-09-15BH14102TTHM36.7 ppb
2014-09-15BH14103TTHM36.5 ppb
2014-09-15BH14104TTHM44.5 ppb
2014-12-17BH54708TTHM24.5 ppb
2014-12-17BH54709TTHM38.3 ppb
2014-12-17BH54710TTHM41.5 ppb
2014-12-17BH54711TTHM40.1 ppb
2015-03-11BH82212TTHM21.4 ppb
2015-03-11BH82210TTHM19.0 ppb
2015-03-11BH82209TTHM16.4 ppb
2015-03-11BH82211TTHM22.8 ppb
2015-06-16BJ31716TTHM43.8 ppb
2015-06-16BJ31718TTHM45.7 ppb
2015-06-16BJ31715TTHM32.2 ppb
2015-06-16BJ31717TTHM41.2 ppb
2015-09-15BJ92119TTHM31.5 ppb
2015-09-15BJ92120TTHM42.9 ppb
2015-09-15BJ92121TTHM44.2 ppb
2015-09-15BJ92122TTHM49.1 ppb
2015-12-08BK34310TTHM34.3 ppb
2015-12-08BK34309TTHM25.3 ppb
2015-12-08BK34311TTHM32.6 ppb
2015-12-08BK34312TTHM32.2 ppb
2016-03-15BK78696TTHM27.2 ppb
2016-03-15BK78697TTHM25.1 ppb
2016-03-15BK78692TTHM22.9 ppb
2016-03-15BK78693TTHM18.4 ppb
2016-06-14BN54616TTHM24.3 ppb
2016-06-14BN54617TTHM21.0 ppb
2016-06-14BN54618TTHM28.3 ppb
2016-06-14BN54619TTHM26.1 ppb
2016-09-14BV14928TTHM39.8 ppb
2016-09-14BV14929TTHM36.7 ppb
2016-09-14BV14930TTHM25.3 ppb
2016-09-14BV14931TTHM41.9 ppb
2016-12-15BX06134TTHM30.6 ppb
2016-12-15BX06135TTHM28.5 ppb
2016-12-15BX06136TTHM7.10 ppb
2016-12-15BX06137TTHM26.5 ppb
2017-03-17BX89073TTHM15.0 ppb
2017-03-17BX89076TTHM21.4 ppb
2017-03-17BX89077TTHM20.1 ppb
2017-03-17BX89078TTHM17.7 ppb
2017-06-19BY42240TTHM35.5 ppb
2017-06-19BY42241TTHM56.0 ppb
2017-06-19BY42242TTHM48.0 ppb
2017-06-19BY42243TTHM42.9 ppb
2017-09-14BZ02387TTHM31.4 ppb
2017-09-14BZ02388TTHM47.5 ppb
2017-09-14BZ02389TTHM45.3 ppb
2017-09-14BZ02390TTHM39.1 ppb
2017-12-14BZ60231TTHM40.4 ppb
2017-12-14BZ60232TTHM38.0 ppb
2017-12-14BZ60233TTHM24.2 ppb
2017-12-14BZ60234TTHM31.0 ppb
2018-03-15CA03073TTHM21.3 ppb
2018-03-15CA03074TTHM15.9 ppb
2018-03-15CA03075TTHM23.6 ppb
2018-03-15CA03076TTHM24.7 ppb
2018-06-26CA80045TTHM44.6 ppb
2018-06-26CA80046TTHM40.5 ppb
2018-06-26CA80047TTHM33.7 ppb
2018-06-26CA80048TTHM27.5 ppb
2018-09-12DBP 20050504236.7 ppb
2018-09-12DBP 20050504362.9 ppb
2018-09-12DBP 20050504454.5 ppb
2018-09-12DBP 20050504762.2 ppb
2018-09-13VOC1 200505275ND
2018-09-13VOC1 200505276ND
2018-09-13VOC1 200505266ND
2018-09-19VOC1 2005061163.90 ppb
2018-09-20VOC1 2005063240.600 ppb
2018-12-17DBP 20051623511.8 ppb
2018-12-17DBP 2005162378.90 ppb
2018-12-17DBP 20051623814.8 ppb
2018-12-17DBP 20051623916.9 ppb
2019-03-11DBP 2005241509.10 ppb
2019-03-11DBP 20052415112.9 ppb
2019-03-11DBP 20052415217.2 ppb
2019-03-11DBP 20052415418.2 ppb
2019-06-14DBP 20053667217.9 ppb
2019-06-14DBP 20053667423.4 ppb
2019-06-14DBP 20053668027.7 ppb
2019-06-14DBP 20053668227.4 ppb
2019-09-17DBP 20054947828.6 ppb
2019-09-17DBP 20054947932.7 ppb
2019-09-17DBP 20054948034.8 ppb
2019-09-17DBP 20054948135.5 ppb
2019-12-10DBP 20055964216.1 ppb
2019-12-10DBP 20055964324.6 ppb
2019-12-10DBP 20055964429.1 ppb
2019-12-10DBP 20055964533.5 ppb