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EWG's Tap Water Database

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Chlorate

Washington

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.

 

6

Samples

0

Samples exceeding legal limit (MCL)

0

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
2010N/A00N/A
2011N/A00N/A
2012N/A00N/A
2013N/A00N/A
2014N/A00N/A
2015ND60ND

ppb = parts per billion.

State and national drinking water standards and health guidelines

Health Guideline 210 ppb

The 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
2015-03-11848087-13619ND
2015-03-11848089-13619ND
2015-03-11848091-13619ND
2015-09-22885085-15026ND
2015-09-22885083-15026ND
2015-09-22885087-15026ND