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EWG's Tap Water Database — 2019 UPDATE

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Chlorate

Los Angeles County WW District 4 & 34-Lancaster

Chlorate forms in drinking water as a byproduct of disinfection. Chlorate impairs thyroid function, making chlorate exposure most harmful during pregnancy and childhood. Read More.

In 2002, California scientists proposed an advisory value, called an action level, for chlorate at 200 parts per billion. Between 2013 and 2015, the EPA collected data through the Unregulated Contaminant Monitoring Rule program and found that over 15 percent of water tests from 38 percent of utilities had chlorate levels above a health-protective concentration, which federal scientists defined as 210 parts per billion, nearly equivalent to the California advisory value.

Click here to read more about disinfection byproducts.

 

38

Samples

0

Samples exceeding legal limit (MCL)

3

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
2012N/A00N/A
201337.7 ppb175ND - 260.0 ppb
201453.0 ppb217ND - 290.0 ppb
2015N/A00N/A
2016N/A00N/A
2017N/A00N/A

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 210 ppb

The EWG Health Guideline of 210 ppb for chlorate was defined by the Environmental Protection Agency as a benchmark for testing under the Unregulated Contaminant Monitoring Rule program. This health guideline protects against hormone disruption.

ppb = parts per billion

All test results

Date Lab ID Result
2013-11-14201311150378AM91.0 ppb
2013-11-18201311200623AMND
2013-11-18201311200611AMND
2013-11-18201311210815AMND
2013-11-18201311210801AMND
2013-11-19201311250062AM140.0 ppb
2013-11-19201311250078AMND
2013-11-19201311220608AMND
2013-11-19201311220610AM110.0 ppb
2013-11-20201312020184AM40.0 ppb
2013-11-20201312020193AMND
2013-11-20201311270080AMND
2013-11-20201311270082AMND
2013-11-25201312030254AMND
2013-11-25201312030252AMND
2013-11-25201312040648AMND
2013-11-26201312040650AM260.0 ppb
2014-02-13201402140365AM100.0 ppb
2014-02-13201402140367AM77.0 ppb
2014-05-13201405160338AM290.0 ppb
2014-05-13201405160381AMND
2014-05-13201405160379AMND
2014-05-14201405160355AM98.0 ppb
2014-05-14201405160334AM78.0 ppb
2014-05-14201405190271AMND
2014-05-14201405160332AMND
2014-05-14201405160336AMND
2014-05-14201405220244AMND
2014-05-14201405190269AMND
2014-05-20201405220248AMND
2014-05-20201405230366AMND
2014-05-21201405290634AMND
2014-05-21201405230356AMND
2014-05-21201405230368AMND
2014-05-27201405290650AMND
2014-05-27201405290654AMND
2014-08-07201408120561AM260.0 ppb
2014-08-07201408120547AM210.0 ppb