Chlorate

Cerritos - City, Water Department

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.

MORE ABOUT THIS CONTAMINANT

Samples

Samples exceeding legal limit (MCL)

Samples exceeding
health guidelines

Testing results - average by year

Year	Average result	Samples taken	Detections	Range of results
2013	8.83 ppb	6	1	ND - 53.0 ppb
2014	19.4 ppb	10	4	ND - 66.0 ppb
2015	N/A	0	0	N/A
2016	N/A	0	0	N/A
2017	N/A	0	0	N/A
2018	N/A	0	0	N/A
2019	N/A	0	0	N/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
2013-10-29	2922350	53.0 ppb
2013-10-29	2922360	ND
2013-10-29	2922356	ND
2013-10-29	2922323	ND
2013-10-29	2922332	ND
2013-10-29	2922341	ND
2014-01-28	2965146	41.0 ppb
2014-01-28	2965161	ND
2014-04-23	3014900	52.0 ppb
2014-04-23	3014913	ND
2014-04-23	3014917	ND
2014-04-23	3014873	ND
2014-04-23	3014891	ND
2014-04-23	3014882	ND
2014-07-24	201407250389AM	35.0 ppb
2014-07-24	201407250387AM	66.0 ppb