Chlorate

Cal-water Service Company - Chico

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	108.8 ppb	27	26	ND - 370.0 ppb
2014	67.7 ppb	66	57	ND - 460.0 ppb
2015	ND	1	0	ND
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
2013-07-08	201307090263AM	110.0 ppb
2013-07-09	201307100957AM	120.0 ppb
2013-07-10	201307110729AM	130.0 ppb
2013-07-10	201307110720AM	77.0 ppb
2013-07-23	201307240449AM	370.0 ppb
2013-07-24	201307250293AM	140.0 ppb
2013-08-05	201308060169AM	74.0 ppb
2013-08-05	201308060204AM	70.0 ppb
2013-08-07	201308080292AM	93.0 ppb
2013-08-07	201308080250AM	83.0 ppb
2013-08-14	201308150514AM	53.0 ppb
2013-08-14	201308150414AM	110.0 ppb
2013-08-14	201308150371AM	93.0 ppb
2013-08-20	201308210526AM	220.0 ppb
2013-08-20	201308210540AM	130.0 ppb
2013-08-21	201308220197AM	180.0 ppb
2013-08-21	201308220223AM	ND
2013-08-27	201308290348AM	210.0 ppb
2013-09-17	201309180521AM	110.0 ppb
2013-09-17	201309180765AM	99.0 ppb
2013-09-17	201309180755AM	100.0 ppb
2013-09-18	201309200063AM	77.0 ppb
2013-10-08	201310090669AM	68.0 ppb
2013-10-08	201310090481AM	32.0 ppb
2013-10-08	201310090472AM	54.0 ppb
2013-10-15	201310160271AM	80.0 ppb
2013-10-15	201310160231AM	55.0 ppb
2014-01-07	201401080516AM	46.0 ppb
2014-01-07	201401080497AM	66.0 ppb
2014-01-08	201401090450AM	200.0 ppb
2014-01-14	201401150418AM	52.0 ppb
2014-01-14	201401150434AM	41.0 ppb
2014-01-21	201401220307AM	67.0 ppb
2014-01-22	201401230387AM	21.0 ppb
2014-01-22	201401230433AM	25.0 ppb
2014-01-28	201401290600AM	82.0 ppb
2014-02-11	201402120760AM	ND
2014-02-11	201402120778AM	ND
2014-02-11	201402120802AM	ND
2014-02-11	201402120769AM	ND
2014-02-11	201402120794AM	28.0 ppb
2014-02-12	201402130419AM	32.0 ppb
2014-02-12	201402130409AM	ND
2014-02-12	201402130428AM	26.0 ppb
2014-02-19	201402200378AM	27.0 ppb
2014-02-26	201402270197AM	45.0 ppb
2014-02-26	201402270248AM	35.0 ppb
2014-02-28	201403010105AM	56.0 ppb
2014-03-04	201403050731AM	ND
2014-03-04	201403050608AM	ND
2014-03-04	201403050464AM	38.0 ppb
2014-03-04	201403050443AM	35.0 ppb
2014-03-05	201403060275AM	100.0 ppb
2014-03-17	201403180221AM	41.0 ppb
2014-03-17	201403180313AM	51.0 ppb
2014-03-17	201403180364AM	34.0 ppb
2014-03-18	201403190852AM	58.0 ppb
2014-03-18	201403190837AM	32.0 ppb
2014-04-08	201404090550AM	36.0 ppb
2014-04-08	201404090697AM	ND
2014-04-08	201404090707AM	ND
2014-04-09	201404100696AM	20.0 ppb
2014-04-09	201404100768AM	29.0 ppb
2014-04-09	201404100740AM	37.0 ppb
2014-04-09	201404100811AM	51.0 ppb
2014-04-09	201404100712AM	33.0 ppb
2014-04-22	201404230457AM	20.0 ppb
2014-04-22	201404230622AM	100.0 ppb
2014-04-23	201404240402AM	52.0 ppb
2014-04-23	201404240509AM	32.0 ppb
2014-06-18	201406190416AM	100.0 ppb
2014-07-09	201407100533AM	87.0 ppb
2014-07-09	201407100482AM	71.0 ppb
2014-07-14	201407150442AM	140.0 ppb
2014-08-05	201408060314AM	130.0 ppb
2014-08-05	201408060343AM	130.0 ppb
2014-08-05	201408060377AM	90.0 ppb
2014-08-06	201408070485AM	67.0 ppb
2014-09-09	201409110325AM	240.0 ppb
2014-09-09	201409100884AM	110.0 ppb
2014-09-09	201409110346AM	170.0 ppb
2014-09-10	201409110781AM	76.0 ppb
2014-09-10	201409110681AM	37.0 ppb
2014-09-23	201409240604AM	63.0 ppb
2014-09-24	201409250611AM	130.0 ppb
2014-10-07	201410080528AM	89.0 ppb
2014-10-07	201410080397AM	100.0 ppb
2014-10-07	201410080455AM	98.0 ppb
2014-10-07	201410080400AM	94.0 ppb
2014-10-08	201410090320AM	25.0 ppb
2014-10-15	201410160408AM	460.0 ppb
2014-10-27	201410290067AM	160.0 ppb
2014-12-09	201412100751AM	150.0 ppb
2015-01-13	201501140884AM	ND