Chlorate

Cliffdale West

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
2014	326.8 ppb	98	92	ND - 3,300.0 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
2014-03-10	201403110323AM	320.0 ppb
2014-03-10	201403110248AM	130.0 ppb
2014-03-10	201403110492AM	200.0 ppb
2014-03-10	201403110485AM	110.0 ppb
2014-03-11	201403120601AM	190.0 ppb
2014-03-11	201403120770AM	210.0 ppb
2014-03-11	201403121138AM	130.0 ppb
2014-03-11	201403120774AM	110.0 ppb
2014-03-12	201403130416AM	130.0 ppb
2014-03-12	201403130412AM	73.0 ppb
2014-03-12	201403130414AM	ND
2014-03-13	201403130209AM	200.0 ppb
2014-03-13	201403140275AM	120.0 ppb
2014-03-13	201403140170AM	140.0 ppb
2014-03-13	201403140164AM	610.0 ppb
2014-03-17	201403180227AM	190.0 ppb
2014-03-17	201403180201AM	200.0 ppb
2014-03-17	201403180203AM	440.0 ppb
2014-03-18	201403190634AM	250.0 ppb
2014-03-18	201403190659AM	310.0 ppb
2014-03-18	201403190705AM	170.0 ppb
2014-03-18	201403190651AM	170.0 ppb
2014-03-18	201403190653AM	110.0 ppb
2014-03-18	201403190657AM	110.0 ppb
2014-03-18	201403190640AM	270.0 ppb
2014-03-19	201403200581AM	3,100.0 ppb
2014-03-19	201403200250AM	190.0 ppb
2014-03-19	201403200273AM	180.0 ppb
2014-03-24	201403250156AM	160.0 ppb
2014-03-25	201403260356AM	160.0 ppb
2014-03-25	201403260307AM	130.0 ppb
2014-03-25	201403260305AM	160.0 ppb
2014-03-25	201403260283AM	110.0 ppb
2014-03-31	201404010144AM	130.0 ppb
2014-04-08	201404090755AM	61.0 ppb
2014-04-08	201404090604AM	290.0 ppb
2014-04-08	201404090616AM	120.0 ppb
2014-04-08	201404090599AM	ND
2014-04-09	201404100673AM	180.0 ppb
2014-04-09	201404100632AM	280.0 ppb
2014-04-09	201404100654AM	150.0 ppb
2014-04-09	201404100603AM	160.0 ppb
2014-04-09	201404100643AM	170.0 ppb
2014-04-30	201405020280AM	260.0 ppb
2014-04-30	201405020282AM	360.0 ppb
2014-04-30	201405020286AM	100.0 ppb
2014-09-09	201409110337AM	260.0 ppb
2014-09-09	201409100887AM	300.0 ppb
2014-09-09	201409100869AM	570.0 ppb
2014-09-09	201409101002AM	1,300.0 ppb
2014-09-09	201409100791AM	240.0 ppb
2014-09-09	201409110315AM	250.0 ppb
2014-09-09	201409100817AM	520.0 ppb
2014-09-09	201409100871AM	430.0 ppb
2014-09-10	201409110899AM	310.0 ppb
2014-09-10	201409110838AM	330.0 ppb
2014-09-10	201409110794AM	320.0 ppb
2014-09-10	201409110590AM	640.0 ppb
2014-09-10	201409110661AM	330.0 ppb
2014-09-10	201409110653AM	300.0 ppb
2014-09-10	201409110637AM	340.0 ppb
2014-09-11	201409120590AM	43.0 ppb
2014-09-11	201409120829AM	350.0 ppb
2014-09-11	201409120582AM	250.0 ppb
2014-09-15	201409180321AM	330.0 ppb
2014-09-16	201409170728AM	580.0 ppb
2014-09-17	201409190242AM	3,300.0 ppb
2014-09-17	201409180633AM	ND
2014-09-17	201409190284AM	ND
2014-09-17	201409190313AM	180.0 ppb
2014-09-18	201409190466AM	ND
2014-09-18	201409190445AM	ND
2014-09-18	201409190399AM	550.0 ppb
2014-09-18	201409190404AM	440.0 ppb
2014-09-18	201409190458AM	71.0 ppb
2014-09-24	201409250521AM	230.0 ppb
2014-09-24	201409250578AM	220.0 ppb
2014-09-24	201409250576AM	240.0 ppb
2014-09-24	201409250574AM	330.0 ppb
2014-09-24	201409250523AM	270.0 ppb
2014-09-24	201409250580AM	240.0 ppb
2014-09-24	201409250533AM	270.0 ppb
2014-09-24	201409250585AM	220.0 ppb
2014-09-24	201409250508AM	310.0 ppb
2014-09-24	201409250527AM	270.0 ppb
2014-09-25	201409260342AM	350.0 ppb
2014-09-25	201409260392AM	350.0 ppb
2014-09-25	201409260496AM	350.0 ppb
2014-09-25	201409260358AM	300.0 ppb
2014-09-25	201409260338AM	300.0 ppb
2014-09-25	201409260369AM	350.0 ppb
2014-09-25	201409260378AM	310.0 ppb
2014-09-25	201409260381AM	390.0 ppb
2014-10-29	201410300238AM	310.0 ppb
2014-10-29	201410300236AM	1,600.0 ppb
2014-11-13	201411150160AM	340.0 ppb
2014-11-13	201411150162AM	310.0 ppb
2014-11-13	201411150164AM	290.0 ppb