EWG's Tap Water Database — 2021 UPDATE


Total trihalomethanes (TTHMs)

Town of Apex

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.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
201429.6 ppb202018.0 ppb - 49.0 ppb
201536.1 ppb161619.0 ppb - 49.0 ppb
201636.9 ppb161627.4 ppb - 56.0 ppb
201744.4 ppb202029.0 ppb - 64.0 ppb
201850.7 ppb323234.0 ppb - 70.0 ppb
201927.4 ppb393917.6 ppb - 44.0 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
2014-02-119218953900121.0 ppb
2014-02-119218953900318.0 ppb
2014-02-119218953900424.0 ppb
2014-02-119218953900524.0 ppb
2014-05-1492201240001TTH29.0 ppb
2014-05-1492201240002TTH28.0 ppb
2014-05-1492201240003TTH27.0 ppb
2014-05-1492201240004TTH28.0 ppb
2014-05-1492201240001DIS30.0 ppb
2014-05-1492201240002DIS29.0 ppb
2014-05-1492201240003DIS27.0 ppb
2014-05-1492201240004DIS28.0 ppb
2014-08-1492213447001TTH46.0 ppb
2014-08-1492213447002TTH44.0 ppb
2014-08-1492213447003TTH49.0 ppb
2014-08-1492213447004TTH46.0 ppb
2014-11-1292225241001TTH23.0 ppb
2014-11-1292225241002TTH24.0 ppb
2014-11-1292225241003TTH22.0 ppb
2014-11-1292225241004TTH24.0 ppb
2015-02-1121.0 ppb
2015-02-1119.0 ppb
2015-02-1122.0 ppb
2015-02-1120.0 ppb
2015-05-1346.0 ppb
2015-05-1341.0 ppb
2015-05-1343.0 ppb
2015-05-1349.0 ppb
2015-08-1444.0 ppb
2015-08-1443.0 ppb
2015-08-1445.0 ppb
2015-08-1447.0 ppb
2015-11-1235.5 ppb
2015-11-1234.4 ppb
2015-11-1237.5 ppb
2015-11-1229.6 ppb
2016-02-1292286426001TTH37.5 ppb
2016-02-1292286426003TTH32.8 ppb
2016-02-1292286426004TTH36.0 ppb
2016-02-1292286426005TTH36.0 ppb
2016-05-1192297108001TTH32.3 ppb
2016-05-1192297108003TTH35.2 ppb
2016-05-1192297108004TTH32.8 ppb
2016-05-1192297108005TTH32.4 ppb
2016-08-1792309277001TTH54.9 ppb
2016-08-1792309277002TTH39.7 ppb
2016-08-1792309277003TTH50.8 ppb
2016-08-1792309277004TTH56.0 ppb
2016-11-1692319879001TTH27.6 ppb
2016-11-1692319879002TTH27.4 ppb
2016-11-1692319879004TTH29.9 ppb
2016-11-1692319879005TTH29.0 ppb
2017-02-1592329986001TTH33.0 ppb
2017-02-1592329986002TTH33.0 ppb
2017-02-1592329986004TTH32.0 ppb
2017-02-1592329986005TTH29.0 ppb
2017-05-1292340418001TTH54.0 ppb
2017-05-1292340418002TTH54.0 ppb
2017-05-1292340418004TTH51.0 ppb
2017-05-1292340418005TTH50.0 ppb
2017-08-1692351687001TTH61.0 ppb
2017-08-1692351687002TTH64.0 ppb
2017-08-1692351687003TTH63.0 ppb
2017-08-1692351687005TTH59.0 ppb
2017-11-1492363203001TTH37.0 ppb
2017-11-1492363203002TTH42.0 ppb
2017-11-1492363203003TTH37.0 ppb
2017-11-1492363203004TTH38.0 ppb
2017-11-1492363203005TTH36.0 ppb
2017-11-1492363203006TTH40.0 ppb
2017-11-1492363203007TTH42.0 ppb
2017-11-1492363203008TTH32.0 ppb
2018-02-1492373327001TTH 40.0 ppb
2018-02-1492373327002TTH 39.0 ppb
2018-02-1492373327003TTH 40.0 ppb
2018-02-1492373327004TTH 45.0 ppb
2018-02-1492373327005TTH 40.0 ppb
2018-02-1492373327006TTH 39.0 ppb
2018-02-1492373327007TTH 40.0 ppb
2018-02-1492373327008TTH 45.0 ppb
2018-05-1692384990001TTH 70.0 ppb
2018-05-1692384990002TTH 62.0 ppb
2018-05-1692384990003TTH 58.0 ppb
2018-05-1692384990004TTH 62.0 ppb
2018-05-1692384990005TTH 67.0 ppb
2018-05-1692384990006TTH 65.0 ppb
2018-05-1692384990007TTH 65.0 ppb
2018-05-1692384990008TTH 57.0 ppb
2018-08-1492395647001TTH 59.0 ppb
2018-08-1492395647002TTH 66.0 ppb
2018-08-1492395647003TTH 58.0 ppb
2018-08-1492395647004TTH 58.0 ppb
2018-08-1492395647005TTH 65.0 ppb
2018-08-1492395647006TTH 60.0 ppb
2018-08-1492395647007TTH 65.0 ppb
2018-08-1492395647008TTH 58.0 ppb
2018-11-1692407681001TTH 37.0 ppb
2018-11-1692407681002TTH 37.0 ppb
2018-11-1692407681003TTH 37.0 ppb
2018-11-1692407681004TTH 35.0 ppb
2018-11-1692407681005TTH 34.0 ppb
2018-11-1692407681006TTH 43.0 ppb
2018-11-1692407681007TTH 38.0 ppb
2018-11-1692407681008TTH 38.0 ppb
2019-02-1492417771001_377019.2 ppb
2019-02-1492417771001_377019.2 ppb
2019-02-1492417771002_377018.0 ppb
2019-02-1492417771002_377018.0 ppb
2019-02-1492417771004_377018.1 ppb
2019-02-1492417771004_377018.1 ppb
2019-02-1492417771005_377018.0 ppb
2019-02-1492417771005_377018.0 ppb
2019-02-1492417771006_377017.6 ppb
2019-02-1492417771006_377017.6 ppb
2019-02-1492417771007_377020.3 ppb
2019-02-1492417771007_377020.3 ppb
2019-02-1492417771008_377018.0 ppb
2019-02-1492417771009_377018.0 ppb
2019-02-1492417771009_377018.0 ppb
2019-05-1592429303001_377040.0 ppb
2019-05-1592429303002_377040.0 ppb
2019-05-1592429303003_377040.0 ppb
2019-05-1592429303004_377039.0 ppb
2019-05-1592429303005_377044.0 ppb
2019-05-1592429303006_377041.0 ppb
2019-05-1592429303007_377041.0 ppb
2019-05-1592429303008_377036.0 ppb
2019-09-2592446996002_377030.0 ppb
2019-09-2592446996003_377039.0 ppb
2019-09-2592446996004_377028.0 ppb
2019-09-2592446996005_377028.0 ppb
2019-09-2592446996006_377029.0 ppb
2019-09-2592446996007_377028.0 ppb
2019-09-2592446996008_377028.0 ppb
2019-09-2592446996009_377029.0 ppb
2019-11-1392453473001_377030.0 ppb
2019-11-1392453473002_377029.0 ppb
2019-11-1392453473003_377029.0 ppb
2019-11-1392453473004_377028.0 ppb
2019-11-1392453473005_377031.0 ppb
2019-11-1392453473006_377027.0 ppb
2019-11-1392453473007_377029.0 ppb
2019-11-1392453473008_377029.0 ppb