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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

Seacoast Utilities 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.

MORE ABOUT THIS CONTAMINANT

 

156

Samples

0

Samples exceeding legal limit (MCL)

152

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
2013N/A00N/A
201416.7 ppb24240.250 ppb - 25.3 ppb
20151.36 ppb35350.250 ppb - 2.20 ppb
20160.778 ppb2423ND - 1.60 ppb
20171.60 ppb2421ND - 3.60 ppb
20181.20 ppb25250.300 ppb - 2.40 ppb
20192.33 ppb24240.320 ppb - 4.70 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 Result
2014-02-1322.5 ppb
2014-02-1325.3 ppb
2014-02-1315.7 ppb
2014-02-1321.7 ppb
2014-02-1325.2 ppb
2014-05-1214.7 ppb
2014-05-1217.3 ppb
2014-05-1221.6 ppb
2014-05-1217.5 ppb
2014-05-1215.8 ppb
2014-05-1214.8 ppb
2014-08-1215.7 ppb
2014-08-1218.3 ppb
2014-08-1219.0 ppb
2014-08-1218.1 ppb
2014-08-1216.4 ppb
2014-08-1212.2 ppb
2014-11-1814.3 ppb
2014-11-180.250 ppb
2014-11-1815.6 ppb
2014-11-1815.7 ppb
2014-11-1815.0 ppb
2014-11-1814.2 ppb
2014-11-1813.6 ppb
2015-02-090.880 ppb
2015-02-092.20 ppb
2015-02-092.20 ppb
2015-02-091.60 ppb
2015-02-091.50 ppb
2015-02-091.90 ppb
2015-05-131.90 ppb
2015-05-131.90 ppb
2015-05-131.90 ppb
2015-05-131.90 ppb
2015-05-131.20 ppb
2015-05-131.20 ppb
2015-05-131.20 ppb
2015-05-131.80 ppb
2015-05-131.80 ppb
2015-05-131.60 ppb
2015-05-131.60 ppb
2015-05-131.90 ppb
2015-05-131.90 ppb
2015-08-121.30 ppb
2015-08-121.30 ppb
2015-08-120.830 ppb
2015-08-120.830 ppb
2015-08-121.40 ppb
2015-08-121.40 ppb
2015-08-121.30 ppb
2015-08-121.30 ppb
2015-08-121.20 ppb
2015-08-121.30 ppb
2015-11-120.600 ppb
2015-11-120.780 ppb
2015-11-120.700 ppb
2015-11-120.740 ppb
2015-11-120.250 ppb
2015-11-120.250 ppb
2016-02-180.250 ppb
2016-02-181.60 ppb
2016-02-180.250 ppb
2016-02-180.250 ppb
2016-02-180.920 ppb
2016-02-181.20 ppb
2016-05-120.980 ppb
2016-05-120.900 ppb
2016-05-120.780 ppb
2016-05-120.950 ppb
2016-05-12ND
2016-05-120.760 ppb
2016-08-100.910 ppb
2016-08-100.840 ppb
2016-08-101.30 ppb
2016-08-100.800 ppb
2016-08-101.20 ppb
2016-08-101.30 ppb
2016-11-100.620 ppb
2016-11-100.700 ppb
2016-11-100.610 ppb
2016-11-100.650 ppb
2016-11-100.250 ppb
2016-11-100.650 ppb
2017-02-081.40 ppb
2017-02-080.830 ppb
2017-02-083.60 ppb
2017-02-080.250 ppb
2017-02-080.820 ppb
2017-02-080.720 ppb
2017-05-180.490 ppb
2017-05-18ND
2017-05-18ND
2017-05-18ND
2017-05-180.680 ppb
2017-05-180.760 ppb
2017-08-082.50 ppb
2017-08-081.90 ppb
2017-08-082.80 ppb
2017-08-082.20 ppb
2017-08-082.80 ppb
2017-08-081.80 ppb
2017-08-081.90 ppb
2017-08-082.50 ppb
2017-08-083.20 ppb
2017-08-082.20 ppb
2017-08-083.20 ppb
2017-08-091.80 ppb
2018-02-270.790 ppb
2018-02-270.830 ppb
2018-02-270.940 ppb
2018-02-270.980 ppb
2018-02-270.750 ppb
2018-02-270.990 ppb
2018-05-091.20 ppb
2018-05-091.000 ppb
2018-05-091.000 ppb
2018-05-091.000 ppb
2018-05-091.20 ppb
2018-05-091.10 ppb
2018-05-091.30 ppb
2018-08-080.870 ppb
2018-08-081.000 ppb
2018-08-080.850 ppb
2018-08-080.900 ppb
2018-08-080.710 ppb
2018-08-080.990 ppb
2018-11-152.20 ppb
2018-11-150.300 ppb
2018-11-152.20 ppb
2018-11-152.30 ppb
2018-11-152.10 ppb
2018-11-152.40 ppb
2019-02-200.930 ppb
2019-02-200.960 ppb
2019-02-201.10 ppb
2019-02-200.900 ppb
2019-02-200.810 ppb
2019-02-221.10 ppb
2019-05-082.60 ppb
2019-05-081.40 ppb
2019-05-081.50 ppb
2019-05-081.80 ppb
2019-05-080.320 ppb
2019-05-081.30 ppb
2019-08-154.50 ppb
2019-08-154.10 ppb
2019-08-153.60 ppb
2019-08-154.00 ppb
2019-08-154.70 ppb
2019-08-154.20 ppb
2019-11-192.40 ppb
2019-11-193.00 ppb
2019-11-192.50 ppb
2019-11-192.60 ppb
2019-11-192.60 ppb
2019-11-192.90 ppb