Chlorate

Town of Gilbert

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.

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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	33.9 ppb	62	44	ND - 100.0 ppb
2014	46.0 ppb	4	2	ND - 96.0 ppb
2015	10.00 ppb	2	1	ND - 20.0 ppb
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
2013-04-22	201304220123AM	24.0 ppb
2013-04-22	201304220129AM	24.0 ppb
2013-04-22	201304220127AM	26.0 ppb
2013-04-22	201304220125AM	23.0 ppb
2013-04-22	201304220108AM	ND
2013-04-22	201304220110AM	85.0 ppb
2013-04-22	201304220119AM	25.0 ppb
2013-04-22	201304220121AM	23.0 ppb
2013-04-23	201304230228AM	86.0 ppb
2013-04-23	201304230213AM	26.0 ppb
2013-04-23	201304230225AM	44.0 ppb
2013-04-23	201304230223AM	81.0 ppb
2013-04-23	201304230221AM	72.0 ppb
2013-04-23	201304230217AM	53.0 ppb
2013-04-23	201304230219AM	ND
2013-04-23	201304230215AM	ND
2013-04-23	201304230211AM	ND
2013-04-24	201304240155AM	25.0 ppb
2013-04-24	201304240159AM	79.0 ppb
2013-04-24	201304240169AM	ND
2013-04-24	201304240167AM	ND
2013-04-24	201304240157AM	28.0 ppb
2013-04-24	201304240163AM	ND
2013-04-24	201304240161AM	ND
2013-04-24	201304240165AM	72.0 ppb
2013-04-25	201304250474AM	ND
2013-04-25	201304250476AM	51.0 ppb
2013-04-25	201304250480AM	71.0 ppb
2013-04-25	201304250478AM	ND
2013-07-25	201307250333AM	50.0 ppb
2013-07-25	201307250327AM	ND
2013-07-25	201307250329AM	ND
2013-07-25	201307250331AM	96.0 ppb
2013-10-14	201310140290AM	31.0 ppb
2013-10-14	201310140278AM	99.0 ppb
2013-10-14	201310140288AM	45.0 ppb
2013-10-14	201310140294AM	100.0 ppb
2013-10-14	201310140292AM	ND
2013-10-14	201310140286AM	25.0 ppb
2013-10-14	201310140284AM	21.0 ppb
2013-10-14	201310140282AM	37.0 ppb
2013-10-14	201310140280AM	22.0 ppb
2013-10-14	201310140276AM	ND
2013-10-15	201310150554AM	49.0 ppb
2013-10-15	201310150552AM	31.0 ppb
2013-10-15	201310150556AM	84.0 ppb
2013-10-15	201310150548AM	26.0 ppb
2013-10-15	201310150550AM	37.0 ppb
2013-10-15	201310150546AM	36.0 ppb
2013-10-16	201310160457AM	68.0 ppb
2013-10-16	201310160455AM	44.0 ppb
2013-10-16	201310160451AM	33.0 ppb
2013-10-16	201310160453AM	68.0 ppb
2013-10-22	201310220324AM	41.0 ppb
2013-10-22	201310220322AM	36.0 ppb
2013-10-22	201310220320AM	26.0 ppb
2013-10-22	201310220328AM	42.0 ppb
2013-10-22	201310220326AM	ND
2013-10-23	201310230754AM	39.0 ppb
2013-10-23	201310230758AM	ND
2013-10-23	201310230760AM	ND
2013-10-23	201310230756AM	ND
2014-01-09	201401090389AM	ND
2014-01-09	201401090391AM	ND
2014-01-21	201401210282AM	96.0 ppb
2014-01-21	201401210278AM	88.0 ppb
2015-06-15	201506150309AM	ND
2015-12-13	201512140112AM	20.0 ppb