Chlorate

Honolulu-Windward-Pearl Harbor

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

109

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	29.0 ppb	107	71	ND - 160.0 ppb
2014	35.5 ppb	2	2	30.0 ppb - 41.0 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
2013-04-01	201304030421AM	ND
2013-04-01	201304030419AM	26.0 ppb
2013-04-01	201304030417AM	30.0 ppb
2013-04-01	201304030423AM	ND
2013-04-02	201304040561AM	30.0 ppb
2013-04-02	201304040555AM	21.0 ppb
2013-04-02	201304040551AM	30.0 ppb
2013-04-02	201304040557AM	ND
2013-04-02	201304040553AM	50.0 ppb
2013-04-02	201304040559AM	47.0 ppb
2013-04-02	201304040549AM	27.0 ppb
2013-04-03	201304050212AM	28.0 ppb
2013-04-03	201304050216AM	28.0 ppb
2013-04-03	201304050214AM	ND
2013-04-03	201304050206AM	ND
2013-04-03	201304050210AM	24.0 ppb
2013-04-03	201304050208AM	35.0 ppb
2013-04-05	201304090174AM	ND
2013-04-05	201304090178AM	42.0 ppb
2013-04-05	201304090180AM	51.0 ppb
2013-04-05	201304090182AM	ND
2013-04-05	201304090176AM	34.0 ppb
2013-04-08	201304100359AM	27.0 ppb
2013-04-08	201304100367AM	ND
2013-04-08	201304100361AM	ND
2013-04-08	201304100365AM	ND
2013-04-08	201304100363AM	ND
2013-04-08	201304100357AM	29.0 ppb
2013-04-09	201304110566AM	52.0 ppb
2013-04-09	201304110570AM	160.0 ppb
2013-04-09	201304110572AM	67.0 ppb
2013-04-09	201304110568AM	ND
2013-04-10	201304120417AM	ND
2013-04-10	201304120419AM	ND
2013-04-10	201304120421AM	30.0 ppb
2013-04-12	201304160082AM	35.0 ppb
2013-04-12	201304160086AM	29.0 ppb
2013-04-12	201304160070AM	ND
2013-04-15	201304170635AM	ND
2013-04-15	201304170633AM	23.0 ppb
2013-04-16	201304180489AM	ND
2013-04-16	201304180487AM	ND
2013-04-17	201304190454AM	22.0 ppb
2013-04-17	201304190456AM	23.0 ppb
2013-04-19	201304230198AM	110.0 ppb
2013-04-19	201304230200AM	ND
2013-04-22	201304240299AM	36.0 ppb
2013-04-22	201304240301AM	28.0 ppb
2013-04-23	201304250519AM	ND
2013-04-24	201304260160AM	83.0 ppb
2013-04-24	201304260158AM	42.0 ppb
2013-04-26	201304300275AM	42.0 ppb
2013-04-26	201304300183AM	22.0 ppb
2013-10-01	201310030508AM	24.0 ppb
2013-10-01	201310030504AM	150.0 ppb
2013-10-01	201310030506AM	33.0 ppb
2013-10-01	201310030502AM	34.0 ppb
2013-10-02	201310040387AM	ND
2013-10-02	201310040383AM	23.0 ppb
2013-10-02	201310040385AM	24.0 ppb
2013-10-04	201310080411AM	ND
2013-10-04	201310080415AM	49.0 ppb
2013-10-04	201310080413AM	ND
2013-10-04	201310080419AM	ND
2013-10-04	201310080417AM	27.0 ppb
2013-10-04	201310080421AM	72.0 ppb
2013-10-07	201310090449AM	37.0 ppb
2013-10-07	201310090445AM	32.0 ppb
2013-10-07	201310090447AM	81.0 ppb
2013-10-08	201310100584AM	30.0 ppb
2013-10-08	201310100582AM	32.0 ppb
2013-10-08	201310100578AM	56.0 ppb
2013-10-08	201310100580AM	55.0 ppb
2013-10-09	201310110394AM	46.0 ppb
2013-10-09	201310110396AM	46.0 ppb
2013-10-11	201310150231AM	65.0 ppb
2013-10-11	201310150225AM	30.0 ppb
2013-10-11	201310150229AM	ND
2013-10-11	201310150233AM	43.0 ppb
2013-10-11	201310150227AM	38.0 ppb
2013-10-14	201310160251AM	38.0 ppb
2013-10-14	201310160255AM	ND
2013-10-14	201310160257AM	22.0 ppb
2013-10-14	201310160253AM	40.0 ppb
2013-10-15	201310170263AM	ND
2013-10-16	201310180369AM	ND
2013-10-16	201310180365AM	38.0 ppb
2013-10-16	201310180363AM	50.0 ppb
2013-10-16	201310180367AM	51.0 ppb
2013-10-16	201310180456AM	33.0 ppb
2013-10-16	201310180458AM	56.0 ppb
2013-10-16	201310180371AM	ND
2013-10-16	201310180361AM	44.0 ppb
2013-10-18	201310220217AM	20.0 ppb
2013-10-18	201310220215AM	ND
2013-10-18	201310220219AM	29.0 ppb
2013-10-18	201310220228AM	38.0 ppb
2013-10-21	201310230542AM	ND
2013-10-21	201310230540AM	ND
2013-10-21	201310230538AM	22.0 ppb
2013-10-21	201310230577AM	ND
2013-10-21	201310230575AM	100.0 ppb
2013-10-22	201310240443AM	ND
2013-10-22	201310240445AM	ND
2013-10-23	201310250245AM	84.0 ppb
2013-10-23	201310250247AM	47.0 ppb
2013-10-23	201310250249AM	ND
2014-04-09	201404120300AM	41.0 ppb
2014-07-15	201407170569AM	30.0 ppb