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EWG's Tap Water Database — 2019 UPDATE

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Total trihalomethanes (TTHMs)

City of Nampa

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.

 

92

Samples

0

Samples exceeding legal limit (MCL)

56

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20123.99 ppb12120.700 ppb - 9.30 ppb
20132.43 ppb168ND - 7.70 ppb
20141.56 ppb166ND - 7.90 ppb
20151.46 ppb168ND - 3.50 ppb
20161.96 ppb169ND - 5.50 ppb
20172.95 ppb1613ND - 9.89 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
2012-02-27D585460.700 ppb
2012-02-27D585471.000 ppb
2012-06-06D605665.60 ppb
2012-06-06D605672.30 ppb
2012-06-06D605654.20 ppb
2012-06-20D609242.40 ppb
2012-09-19D629652.30 ppb
2012-09-19D629664.50 ppb
2012-11-07D638682.60 ppb
2012-11-07D638705.10 ppb
2012-11-07D638697.90 ppb
2012-11-07D638679.30 ppb
2013-02-20D1307227ND
2013-02-20D1307226ND
2013-02-20D1307228ND
2013-02-20D1307225ND
2013-05-02D13189044.80 ppb
2013-05-02D13189037.70 ppb
2013-05-02D1318902ND
2013-05-02D13189012.70 ppb
2013-08-27D1336972ND
2013-08-27D13369716.60 ppb
2013-08-27D1336973ND
2013-08-27D13369743.80 ppb
2013-11-13D1348399ND
2013-11-13D13483984.10 ppb
2013-11-13D13483972.80 ppb
2013-11-13D13483966.40 ppb
2014-02-20D1406359ND
2014-02-20D1406358ND
2014-02-20D1406357ND
2014-02-20D1406356ND
2014-05-14D1417170ND
2014-05-14D1417171ND
2014-05-14D14171722.10 ppb
2014-05-14D1417173ND
2014-08-19D14323354.30 ppb
2014-08-19D14323347.90 ppb
2014-08-19D14323332.80 ppb
2014-08-19D1432332ND
2014-11-18D1445847ND
2014-11-18D1445848ND
2014-11-18D14458494.60 ppb
2014-11-18D14458503.20 ppb
2015-02-24D15071192.00 ppb
2015-02-24D15071203.30 ppb
2015-02-24D1507121ND
2015-02-24D15071223.50 ppb
2015-06-09D1522390ND
2015-06-09D15223893.00 ppb
2015-06-09D1522387ND
2015-06-09D1522388ND
2015-09-01D1537283ND
2015-09-01D15372842.50 ppb
2015-09-01D1537285ND
2015-09-01D15372863.30 ppb
2015-11-18D1550142ND
2015-11-18D15501432.50 ppb
2015-11-18D1550144ND
2015-11-18D15501453.20 ppb
2016-02-16D1606319ND
2016-02-16D1606318ND
2016-02-16D16063172.20 ppb
2016-02-16D16063162.20 ppb
2016-04-20D1616217ND
2016-04-20D1616218ND
2016-04-20D16162193.10 ppb
2016-04-20D16162202.90 ppb
2016-07-14D1631271ND
2016-07-14D16312724.70 ppb
2016-07-14D1631273ND
2016-07-14D16312745.10 ppb
2016-10-07D16461771.80 ppb
2016-10-07D1646176ND
2016-10-07D16461795.50 ppb
2016-10-07D16461783.80 ppb
2017-01-31D17038081.10 ppb
2017-01-31D1703807ND
2017-01-31D17038090.800 ppb
2017-01-31D1703810ND
2017-04-11D17144170.700 ppb
2017-04-11D17144181.40 ppb
2017-04-11D17144192.50 ppb
2017-04-11D17144201.27 ppb
2017-08-09D1735771ND
2017-08-09D17357724.55 ppb
2017-08-09D17357736.63 ppb
2017-08-09D17357746.08 ppb
2017-10-18D17487590.520 ppb
2017-10-18D17487607.05 ppb
2017-10-18D17487614.74 ppb
2017-10-18D17487629.89 ppb