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EWG's Tap Water Database — 2019 UPDATE

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Total trihalomethanes (TTHMs)

Cedar City Waterworks

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.

 

15

Samples

0

Samples exceeding legal limit (MCL)

15

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20123.75 ppb222.70 ppb - 4.80 ppb
20132.20 ppb221.10 ppb - 3.30 ppb
20142.20 ppb330.500 ppb - 3.90 ppb
20151.80 ppb221.30 ppb - 2.30 ppb
20162.50 ppb222.20 ppb - 2.80 ppb
20175.08 ppb442.80 ppb - 9.80 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
2012-09-182.70 ppb
2012-09-184.80 ppb
2013-08-223.30 ppb
2013-08-221.10 ppb
2014-08-262.20 ppb
2014-08-260.500 ppb
2014-11-263.90 ppb
2015-09-151.30 ppb
2015-09-152.30 ppb
2016-06-142.80 ppb
2016-06-142.20 ppb
2017-05-153.90 ppb
2017-07-253.80 ppb
2017-07-252.80 ppb
2017-10-309.80 ppb