Chlorate

City of Mesa

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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128

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	94.0 ppb	120	81	ND - 440.0 ppb
2014	98.8 ppb	6	5	ND - 170.0 ppb
2015	130.0 ppb	2	2	120.0 ppb - 140.0 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
2013-01-15	201301160556AM	ND
2013-01-15	201301160548AM	ND
2013-01-15	201301160554AM	ND
2013-01-16	201301160558AM	23.0 ppb
2013-01-16	201301160560AM	340.0 ppb
2013-01-16	201301160562AM	ND
2013-01-16	201301160566AM	ND
2013-01-16	201301160564AM	ND
2013-01-22	201301240174AM	ND
2013-01-22	201301240176AM	330.0 ppb
2013-01-22	201301240172AM	240.0 ppb
2013-01-22	201301240152AM	ND
2013-01-23	201301240197AM	300.0 ppb
2013-01-23	201301240195AM	120.0 ppb
2013-01-30	201301310433AM	ND
2013-01-30	201301310431AM	410.0 ppb
2013-02-12	201302140551AM	21.0 ppb
2013-02-12	201302140549AM	150.0 ppb
2013-02-12	201302140542AM	ND
2013-02-12	201302140544AM	ND
2013-02-12	201302140546AM	62.0 ppb
2013-02-13	201302140538AM	210.0 ppb
2013-02-13	201302140540AM	40.0 ppb
2013-02-13	201302140535AM	50.0 ppb
2013-02-13	201302140531AM	28.0 ppb
2013-02-13	201302140529AM	38.0 ppb
2013-02-13	201302140533AM	56.0 ppb
2013-02-19	201302200371AM	130.0 ppb
2013-02-19	201302200375AM	140.0 ppb
2013-02-19	201302200373AM	74.0 ppb
2013-04-08	201304100491AM	250.0 ppb
2013-04-09	201304100493AM	50.0 ppb
2013-04-09	201304100477AM	ND
2013-04-09	201304100479AM	ND
2013-04-09	201304100481AM	22.0 ppb
2013-04-10	201304110554AM	ND
2013-04-10	201304110552AM	160.0 ppb
2013-04-10	201304110546AM	24.0 ppb
2013-04-10	201304110542AM	36.0 ppb
2013-04-10	201304110540AM	35.0 ppb
2013-04-10	201304110544AM	ND
2013-04-16	201304170691AM	57.0 ppb
2013-04-17	201304170697AM	110.0 ppb
2013-04-17	201304170701AM	30.0 ppb
2013-04-17	201304170699AM	320.0 ppb
2013-04-17	201304170695AM	270.0 ppb
2013-05-09	201305100048AM	250.0 ppb
2013-05-09	201305100040AM	ND
2013-05-09	201305100038AM	ND
2013-05-09	201305100042AM	21.0 ppb
2013-05-09	201305100044AM	81.0 ppb
2013-05-09	201305100046AM	56.0 ppb
2013-05-14	201305150463AM	160.0 ppb
2013-05-14	201305150465AM	77.0 ppb
2013-05-15	201305150520AM	68.0 ppb
2013-05-15	201305150518AM	ND
2013-05-20	201305200188AM	100.0 ppb
2013-05-20	201305200190AM	230.0 ppb
2013-05-20	201305200068AM	ND
2013-05-20	201305200127AM	ND
2013-07-09	201307100757AM	330.0 ppb
2013-07-09	201307100755AM	ND
2013-07-10	201307100759AM	190.0 ppb
2013-07-10	201307100761AM	390.0 ppb
2013-07-16	201307170500AM	160.0 ppb
2013-07-16	201307170508AM	ND
2013-07-16	201307170504AM	26.0 ppb
2013-07-16	201307170506AM	ND
2013-07-16	201307170510AM	25.0 ppb
2013-07-17	201307170514AM	110.0 ppb
2013-07-17	201307170512AM	94.0 ppb
2013-07-17	201307170520AM	ND
2013-07-17	201307170518AM	ND
2013-07-17	201307170516AM	21.0 ppb
2013-07-23	201307240533AM	360.0 ppb
2013-07-23	201307240531AM	240.0 ppb
2013-07-24	201307240537AM	ND
2013-07-24	201307240544AM	ND
2013-08-06	201308070603AM	94.0 ppb
2013-08-06	201308070601AM	ND
2013-08-06	201308070586AM	ND
2013-08-06	201308070588AM	ND
2013-08-06	201308070584AM	ND
2013-08-07	201308070605AM	41.0 ppb
2013-08-07	201308070590AM	53.0 ppb
2013-08-13	201308140062AM	260.0 ppb
2013-08-13	201308140060AM	160.0 ppb
2013-08-14	201308140418AM	170.0 ppb
2013-08-14	201308140416AM	61.0 ppb
2013-08-14	201308140394AM	20.0 ppb
2013-08-14	201308140392AM	ND
2013-10-08	201310080650AM	220.0 ppb
2013-10-08	201310080652AM	260.0 ppb
2013-10-08	201310080610AM	ND
2013-10-08	201310080612AM	ND
2013-10-08	201310080614AM	35.0 ppb
2013-10-08	201310080616AM	ND
2013-10-09	201310090515AM	110.0 ppb
2013-10-09	201310090517AM	150.0 ppb
2013-10-09	201310090511AM	ND
2013-10-09	201310090513AM	39.0 ppb
2013-10-15	201310150509AM	55.0 ppb
2013-10-15	201310150507AM	73.0 ppb
2013-10-15	201310150505AM	340.0 ppb
2013-10-15	201310150503AM	300.0 ppb
2013-10-16	201310160477AM	45.0 ppb
2013-10-16	201310160475AM	110.0 ppb
2013-11-05	201311070309AM	320.0 ppb
2013-11-05	201311070311AM	440.0 ppb
2013-11-05	201311050403AM	ND
2013-11-05	201311050401AM	25.0 ppb
2013-11-06	201311070313AM	280.0 ppb
2013-11-06	201311070294AM	70.0 ppb
2013-11-06	201311070298AM	ND
2013-11-06	201311070300AM	33.0 ppb
2013-11-06	201311070296AM	33.0 ppb
2013-11-12	201311130338AM	73.0 ppb
2013-11-12	201311130336AM	160.0 ppb
2013-11-13	201311140713AM	ND
2013-11-20	201311210516AM	140.0 ppb
2014-03-25	201403250421AM	120.0 ppb
2014-03-25	201403250419AM	170.0 ppb
2014-06-04	201406040578AM	160.0 ppb
2014-06-04	201406040576AM	95.0 ppb
2014-09-02	201409020219AM	48.0 ppb
2014-09-02	201409020217AM	ND
2015-01-21	201501220206AM	140.0 ppb
2015-01-21	201501220204AM	120.0 ppb