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.
Testing results - average by year
Year | Average result | Samples taken | Detections | Range of results |
---|---|---|---|---|
2014 | 35.2 ppb | 16 | 16 | 8.50 ppb - 52.9 ppb |
2015 | 33.4 ppb | 16 | 16 | 16.4 ppb - 49.1 ppb |
2016 | 26.9 ppb | 16 | 16 | 7.10 ppb - 41.9 ppb |
2017 | 34.6 ppb | 16 | 16 | 15.0 ppb - 56.0 ppb |
2018 | 24.0 ppb | 21 | 18 | ND - 62.9 ppb |
2019 | 24.3 ppb | 16 | 16 | 9.10 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 |
---|---|---|
2014-03-21 | 3482THM | 15.8 ppb |
2014-03-21 | 3483THM | 8.50 ppb |
2014-03-21 | 3484THM | 25.1 ppb |
2014-03-21 | 3485THM | 33.5 ppb |
2014-06-18 | 8760THM | 45.8 ppb |
2014-06-18 | 8761THM | 52.9 ppb |
2014-06-18 | 8764THM | 44.2 ppb |
2014-06-18 | 8765THM | 45.8 ppb |
2014-09-15 | BH14101TTHM | 29.7 ppb |
2014-09-15 | BH14102TTHM | 36.7 ppb |
2014-09-15 | BH14103TTHM | 36.5 ppb |
2014-09-15 | BH14104TTHM | 44.5 ppb |
2014-12-17 | BH54708TTHM | 24.5 ppb |
2014-12-17 | BH54709TTHM | 38.3 ppb |
2014-12-17 | BH54710TTHM | 41.5 ppb |
2014-12-17 | BH54711TTHM | 40.1 ppb |
2015-03-11 | BH82212TTHM | 21.4 ppb |
2015-03-11 | BH82210TTHM | 19.0 ppb |
2015-03-11 | BH82209TTHM | 16.4 ppb |
2015-03-11 | BH82211TTHM | 22.8 ppb |
2015-06-16 | BJ31716TTHM | 43.8 ppb |
2015-06-16 | BJ31718TTHM | 45.7 ppb |
2015-06-16 | BJ31715TTHM | 32.2 ppb |
2015-06-16 | BJ31717TTHM | 41.2 ppb |
2015-09-15 | BJ92119TTHM | 31.5 ppb |
2015-09-15 | BJ92120TTHM | 42.9 ppb |
2015-09-15 | BJ92121TTHM | 44.2 ppb |
2015-09-15 | BJ92122TTHM | 49.1 ppb |
2015-12-08 | BK34310TTHM | 34.3 ppb |
2015-12-08 | BK34309TTHM | 25.3 ppb |
2015-12-08 | BK34311TTHM | 32.6 ppb |
2015-12-08 | BK34312TTHM | 32.2 ppb |
2016-03-15 | BK78696TTHM | 27.2 ppb |
2016-03-15 | BK78697TTHM | 25.1 ppb |
2016-03-15 | BK78692TTHM | 22.9 ppb |
2016-03-15 | BK78693TTHM | 18.4 ppb |
2016-06-14 | BN54616TTHM | 24.3 ppb |
2016-06-14 | BN54617TTHM | 21.0 ppb |
2016-06-14 | BN54618TTHM | 28.3 ppb |
2016-06-14 | BN54619TTHM | 26.1 ppb |
2016-09-14 | BV14928TTHM | 39.8 ppb |
2016-09-14 | BV14929TTHM | 36.7 ppb |
2016-09-14 | BV14930TTHM | 25.3 ppb |
2016-09-14 | BV14931TTHM | 41.9 ppb |
2016-12-15 | BX06134TTHM | 30.6 ppb |
2016-12-15 | BX06135TTHM | 28.5 ppb |
2016-12-15 | BX06136TTHM | 7.10 ppb |
2016-12-15 | BX06137TTHM | 26.5 ppb |
2017-03-17 | BX89073TTHM | 15.0 ppb |
2017-03-17 | BX89076TTHM | 21.4 ppb |
2017-03-17 | BX89077TTHM | 20.1 ppb |
2017-03-17 | BX89078TTHM | 17.7 ppb |
2017-06-19 | BY42240TTHM | 35.5 ppb |
2017-06-19 | BY42241TTHM | 56.0 ppb |
2017-06-19 | BY42242TTHM | 48.0 ppb |
2017-06-19 | BY42243TTHM | 42.9 ppb |
2017-09-14 | BZ02387TTHM | 31.4 ppb |
2017-09-14 | BZ02388TTHM | 47.5 ppb |
2017-09-14 | BZ02389TTHM | 45.3 ppb |
2017-09-14 | BZ02390TTHM | 39.1 ppb |
2017-12-14 | BZ60231TTHM | 40.4 ppb |
2017-12-14 | BZ60232TTHM | 38.0 ppb |
2017-12-14 | BZ60233TTHM | 24.2 ppb |
2017-12-14 | BZ60234TTHM | 31.0 ppb |
2018-03-15 | CA03073TTHM | 21.3 ppb |
2018-03-15 | CA03074TTHM | 15.9 ppb |
2018-03-15 | CA03075TTHM | 23.6 ppb |
2018-03-15 | CA03076TTHM | 24.7 ppb |
2018-06-26 | CA80045TTHM | 44.6 ppb |
2018-06-26 | CA80046TTHM | 40.5 ppb |
2018-06-26 | CA80047TTHM | 33.7 ppb |
2018-06-26 | CA80048TTHM | 27.5 ppb |
2018-09-12 | DBP 200505042 | 36.7 ppb |
2018-09-12 | DBP 200505043 | 62.9 ppb |
2018-09-12 | DBP 200505044 | 54.5 ppb |
2018-09-12 | DBP 200505047 | 62.2 ppb |
2018-09-13 | VOC1 200505275 | ND |
2018-09-13 | VOC1 200505276 | ND |
2018-09-13 | VOC1 200505266 | ND |
2018-09-19 | VOC1 200506116 | 3.90 ppb |
2018-09-20 | VOC1 200506324 | 0.600 ppb |
2018-12-17 | DBP 200516235 | 11.8 ppb |
2018-12-17 | DBP 200516237 | 8.90 ppb |
2018-12-17 | DBP 200516238 | 14.8 ppb |
2018-12-17 | DBP 200516239 | 16.9 ppb |
2019-03-11 | DBP 200524150 | 9.10 ppb |
2019-03-11 | DBP 200524151 | 12.9 ppb |
2019-03-11 | DBP 200524152 | 17.2 ppb |
2019-03-11 | DBP 200524154 | 18.2 ppb |
2019-06-14 | DBP 200536672 | 17.9 ppb |
2019-06-14 | DBP 200536674 | 23.4 ppb |
2019-06-14 | DBP 200536680 | 27.7 ppb |
2019-06-14 | DBP 200536682 | 27.4 ppb |
2019-09-17 | DBP 200549478 | 28.6 ppb |
2019-09-17 | DBP 200549479 | 32.7 ppb |
2019-09-17 | DBP 200549480 | 34.8 ppb |
2019-09-17 | DBP 200549481 | 35.5 ppb |
2019-12-10 | DBP 200559642 | 16.1 ppb |
2019-12-10 | DBP 200559643 | 24.6 ppb |
2019-12-10 | DBP 200559644 | 29.1 ppb |
2019-12-10 | DBP 200559645 | 33.5 ppb |