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EWG's Tap Water Database — 2019 UPDATE

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Total trihalomethanes (TTHMs)

Watertown City

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.

In 2010, the California Office of Environmental Health Hazard Assessment published a draft public health goal for the trihalomethanes group at 0.8 parts per billion, or 100 times lower than the federal legal limit of 80 parts per billion for this contaminant group.

Click here to read more about disinfection byproducts.

 

211

Samples

55

Samples exceeding legal limit (MCL)

209

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
201268.4 ppb161626.0 ppb - 126.0 ppb
201365.0 ppb161618.0 ppb - 149.0 ppb
201462.3 ppb333316.0 ppb - 141.0 ppb
201549.4 ppb484815.0 ppb - 105.0 ppb
201659.3 ppb484817.0 ppb - 122.0 ppb
201761.9 ppb5048ND - 130.0 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
2012-02-221202714-00449.0 ppb
2012-02-221202714-00330.0 ppb
2012-02-221202714-00226.0 ppb
2012-02-221202714-00145.0 ppb
2012-05-021206534-00354.0 ppb
2012-05-021206534-00176.0 ppb
2012-05-021206534-00481.0 ppb
2012-05-021026534-00253.0 ppb
2012-08-011212371-00299.0 ppb
2012-08-011212371-00979.0 ppb
2012-08-011212371-006126.0 ppb
2012-08-011212371-010108.0 ppb
2012-11-071218302-00691.0 ppb
2012-11-071218302-00947.0 ppb
2012-11-071218302-01057.0 ppb
2012-11-071218302-00274.0 ppb
2013-02-061301770-00718.0 ppb
2013-02-061301770-00652.0 ppb
2013-02-061301770-00826.0 ppb
2013-02-061301770-00224.0 ppb
2013-05-08MRT0031 DBP 2QTR80.0 ppb
2013-05-08DS00014 DBP 2QTR58.0 ppb
2013-05-08DS00026 DBP 2QTR60.0 ppb
2013-05-08DS00015 2QTR20158.0 ppb
2013-08-061313147-004149.0 ppb
2013-08-061313147-003139.0 ppb
2013-08-071313147-00292.0 ppb
2013-08-081313147-00179.0 ppb
2013-11-061318290-01247.0 ppb
2013-11-061318290-01143.0 ppb
2013-11-061318290-00762.0 ppb
2013-11-061318290-01053.0 ppb
2014-02-051401657-01216.0 ppb
2014-02-051401657-01116.0 ppb
2014-02-051401657-01017.0 ppb
2014-02-051401657-00725.0 ppb
2014-04-021404398-00926.0 ppb
2014-05-071406257-01141.0 ppb
2014-05-071406257-01243.0 ppb
2014-05-071406257-00150.0 ppb
2014-05-071406257-00443.0 ppb
2014-07-161410755-01190.0 ppb
2014-07-161410755-01279.0 ppb
2014-07-161410755-010102.0 ppb
2014-07-161410755-007141.0 ppb
2014-08-061412351-007114.0 ppb
2014-08-061412351-01281.0 ppb
2014-08-061412351-01184.0 ppb
2014-08-061412351-01096.0 ppb
2014-09-101414832-009104.0 ppb
2014-09-101414832-01170.0 ppb
2014-09-101414832-00884.0 ppb
2014-09-101414832-01273.0 ppb
2014-10-081416618-01252.0 ppb
2014-10-081416618-01048.0 ppb
2014-10-081416618-01149.0 ppb
2014-10-081416618-00772.0 ppb
2014-11-051418303-01073.0 ppb
2014-11-051418303-00791.0 ppb
2014-11-051418303-01153.0 ppb
2014-11-051418303-01261.0 ppb
2014-12-031419724-01238.0 ppb
2014-12-031419724-01136.0 ppb
2014-12-031419724-00829.0 ppb
2014-12-031419724-00958.0 ppb
2015-01-141500772-01021.0 ppb
2015-01-141500772-01216.0 ppb
2015-01-151500772-01115.0 ppb
2015-01-151500772-00728.0 ppb
2015-02-041501522-01116.0 ppb
2015-02-041501522-00825.0 ppb
2015-02-041501522-01218.0 ppb
2015-02-041501522-00926.0 ppb
2015-03-041502825-01021.0 ppb
2015-03-041502825-01117.0 ppb
2015-03-041502825-01215.0 ppb
2015-03-041502825-00728.0 ppb
2015-04-081504564-01224.0 ppb
2015-04-081504564-01026.0 ppb
2015-04-081504564-01122.0 ppb
2015-04-081504564-00727.0 ppb
2015-05-061506084-01257.0 ppb
2015-05-061506084-01057.0 ppb
2015-05-061506084-00756.0 ppb
2015-05-061506084-01157.0 ppb
2015-06-031507791-01238.0 ppb
2015-06-031507791-01038.0 ppb
2015-06-031507791-01151.0 ppb
2015-06-031507791-00754.0 ppb
2015-07-081510103-01171.0 ppb
2015-07-081510103-01268.0 ppb
2015-07-081510103-01073.0 ppb
2015-07-081510103-007104.0 ppb
2015-08-051511980-01268.0 ppb
2015-08-051511980-01162.0 ppb
2015-08-051511980-00793.0 ppb
2015-08-051511980-01074.0 ppb
2015-09-091514301-010105.0 ppb
2015-09-091514301-01281.0 ppb
2015-09-091514301-01179.0 ppb
2015-09-091514301-00795.0 ppb
2015-10-071516030-01247.0 ppb
2015-10-071516030-01142.0 ppb
2015-10-071516030-00648.0 ppb
2015-10-071516030-00961.0 ppb
2015-11-041517576-01072.0 ppb
2015-11-041517576-01149.0 ppb
2015-11-041517576-00768.0 ppb
2015-11-041517576-01251.0 ppb
2015-12-021519086-01138.0 ppb
2015-12-021519086-01243.0 ppb
2015-12-021519086-00761.0 ppb
2015-12-021519086-01067.0 ppb
2016-01-061600312-01121.0 ppb
2016-01-061600312-01036.0 ppb
2016-01-061600312-01225.0 ppb
2016-01-061600312-00733.0 ppb
2016-02-031601638-01225.0 ppb
2016-02-031601638-01024.0 ppb
2016-02-031601638-00734.0 ppb
2016-02-031601638-01124.0 ppb
2016-03-021602966-01017.0 ppb
2016-03-021602966-01219.0 ppb
2016-03-021602966-00726.0 ppb
2016-03-021602966-01118.0 ppb
2016-04-061604789-01239.0 ppb
2016-04-061604789-00745.0 ppb
2016-04-061604789-01050.0 ppb
2016-04-061604789-01141.0 ppb
2016-05-041606613-01076.0 ppb
2016-05-041606613-01154.0 ppb
2016-05-041606613-00786.0 ppb
2016-05-041606613-01248.0 ppb
2016-06-081608681-01454.0 ppb
2016-06-081608681-01360.0 ppb
2016-06-081608681-00980.0 ppb
2016-06-081608681-00682.0 ppb
2016-07-061610588-010114.0 ppb
2016-07-061610588-007107.0 ppb
2016-07-061610588-01187.0 ppb
2016-07-061610588-01283.0 ppb
2016-08-031612539-007115.0 ppb
2016-08-031612539-012103.0 ppb
2016-08-031612539-00964.0 ppb
2016-08-031612539-01065.0 ppb
2016-09-071614875-010117.0 ppb
2016-09-071614875-01175.0 ppb
2016-09-071614875-007122.0 ppb
2016-09-071614875-01276.0 ppb
2016-10-051616823-00267.0 ppb
2016-10-051616823-01248.0 ppb
2016-10-051616823-009118.0 ppb
2016-10-051616823-01149.0 ppb
2016-11-021618348-00783.0 ppb
2016-11-021618348-01051.0 ppb
2016-11-021618348-01248.0 ppb
2016-11-021618348-01143.0 ppb
2016-12-071620270-01234.0 ppb
2016-12-071620270-00243.0 ppb
2016-12-071620270-00985.0 ppb
2016-12-071620270-01133.0 ppb
2017-01-041700403-00420.0 ppb
2017-01-041700403-01145.0 ppb
2017-01-041700403-00319.0 ppb
2017-01-041700403-00226.0 ppb
2017-02-011701549-00220.0 ppb
2017-02-011701549-00428.0 ppb
2017-02-011701549-00341.0 ppb
2017-02-011701549-00118.0 ppb
2017-03-011702919-00222.0 ppb
2017-03-011702919-00121.0 ppb
2017-03-011702919-00342.0 ppb
2017-03-011702919-00423.0 ppb
2017-04-051704744-00135.0 ppb
2017-04-051704744-00427.0 ppb
2017-04-051704744-00327.0 ppb
2017-04-051704744-00244.0 ppb
2017-05-031706368-00359.0 ppb
2017-05-031706368-00182.0 ppb
2017-05-031706368-00471.0 ppb
2017-05-031706368-00257.0 ppb
2017-05-311800236-005ND
2017-05-311801970-005ND
2017-06-071708525-00198.0 ppb
2017-06-071708525-002101.0 ppb
2017-06-071708525-00467.0 ppb
2017-06-071708525-00368.0 ppb
2017-07-051710148-00294.0 ppb
2017-07-051710148-00493.0 ppb
2017-07-051710148-001110.0 ppb
2017-07-051710148-003123.0 ppb
2017-08-021712271-003130.0 ppb
2017-08-021712271-001130.0 ppb
2017-08-021712271-004109.0 ppb
2017-08-021712271-002109.0 ppb
2017-09-061714647-003118.0 ppb
2017-09-061717647-00493.0 ppb
2017-09-061714647-00291.0 ppb
2017-09-061714647-001116.0 ppb
2017-10-041716498-00454.0 ppb
2017-10-041716498-00383.0 ppb
2017-10-041716498-00187.0 ppb
2017-10-041716498-00262.0 ppb
2017-11-011718017-00187.0 ppb
2017-11-011718017-00463.0 ppb
2017-11-011718017-002583.0 ppb
2017-11-011718017-00360.0 ppb
2017-12-061719921-00431.0 ppb
2017-12-061719921-00127.0 ppb
2017-12-061719921-00231.0 ppb
2017-12-061719921-00349.0 ppb