Chlorate
Zone 7 Water Agency
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.
Testing results - average by year
Year | Average result | Samples taken | Detections | Range of results |
---|---|---|---|---|
2014 | 156.3 ppb | 37 | 34 | ND - 588.0 ppb |
2015 | 126.7 ppb | 29 | 29 | 24.0 ppb - 344.0 ppb |
2016 | 99.0 ppb | 43 | 36 | ND - 545.0 ppb |
2017 | 100.8 ppb | 42 | 39 | ND - 329.0 ppb |
2018 | 96.7 ppb | 50 | 50 | 22.0 ppb - 306.0 ppb |
2019 | 99.5 ppb | 48 | 45 | ND - 858.0 ppb |
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 |
---|---|---|
2014-01-06 | 5100-001-0945 | 123.0 ppb |
2014-01-06 | 5100-006-1120 | 66.0 ppb |
2014-01-06 | 5100-008-0915 | 219.0 ppb |
2014-01-06 | 5100-012-1240 | 48.0 ppb |
2014-02-03 | 5100-001-1025 | 152.0 ppb |
2014-02-18 | 5100-008-0950 | 383.0 ppb |
2014-03-24 | 5100-001-1000 | 251.0 ppb |
2014-03-24 | 5100-008-1045 | 241.0 ppb |
2014-04-07 | 5100-001-0940 | 116.0 ppb |
2014-04-07 | 5100-008-1120 | 123.0 ppb |
2014-05-05 | 5100-001-0930 | 167.0 ppb |
2014-05-05 | 5100-008-1035 | 147.0 ppb |
2014-06-09 | 5100-001-1000 | 193.0 ppb |
2014-06-09 | 5100-008-1035 | 223.0 ppb |
2014-06-10 | 5100-005-1000 | 37.0 ppb |
2014-06-10 | 5100-011-1040 | 21.0 ppb |
2014-06-11 | 5100-006-0825 | 32.0 ppb |
2014-06-11 | 5100-013-0930 | 39.0 ppb |
2014-06-16 | 5100-007-0910 | 24.0 ppb |
2014-06-17 | 5100-012-1125 | 46.0 ppb |
2014-06-19 | 5100-019-0935 | 31.0 ppb |
2014-07-07 | 5100-001-1000 | 319.0 ppb |
2014-07-07 | 5100-008-1015 | 311.0 ppb |
2014-08-04 | 5100-001-0950 | 588.0 ppb |
2014-08-04 | 5100-008-1035 | 284.0 ppb |
2014-09-08 | 5100-001-0840 | 339.0 ppb |
2014-09-08 | 5100-006-1150 | ND |
2014-09-09 | 5100-007-0930 | ND |
2014-09-10 | 5100-005-0830 | 39.0 ppb |
2014-09-10 | 5100-011-0800 | ND |
2014-10-06 | 5100-001-1110 | 275.0 ppb |
2014-10-06 | 5100-008-0825 | 333.0 ppb |
2014-11-03 | 5100-001-0935 | 118.0 ppb |
2014-11-03 | 5100-008-0930 | 236.0 ppb |
2014-11-13 | 5100-017-0905 | 54.0 ppb |
2014-12-08 | 5100-001-0905 | 115.0 ppb |
2014-12-08 | 5100-008-1045 | 90.0 ppb |
2015-01-05 | 5100-001-0935 | 106.0 ppb |
2015-01-05 | 5100-008-0945 | 208.0 ppb |
2015-02-02 | 5100-008-0955 | 103.0 ppb |
2015-03-02 | 5100-001-1005 | 44.0 ppb |
2015-03-03 | 5100-017-0825 | 38.0 ppb |
2015-03-24 | 5100-019-1005 | 43.0 ppb |
2015-04-13 | 5100-001-0850 | 133.0 ppb |
2015-04-13 | 5100-008-0840 | 168.0 ppb |
2015-05-04 | 5100-001-0945 | 214.0 ppb |
2015-05-04 | 5100-008-1025 | 135.0 ppb |
2015-06-22 | 5100-001-1100 | 115.0 ppb |
2015-06-22 | 5100-008-0845 | 211.0 ppb |
2015-06-24 | 5100-019-0845 | 33.0 ppb |
2015-06-25 | 5100-017-0955 | 58.0 ppb |
2015-06-26 | 5100-005-0905 | 30.0 ppb |
2015-06-26 | 5100-007-0930 | 24.0 ppb |
2015-07-06 | 5100-001-0855 | 102.0 ppb |
2015-07-06 | 5100-008-1036 | 344.0 ppb |
2015-08-03 | 5100-001-0920 | 146.0 ppb |
2015-08-03 | 5100-008-1010 | 207.0 ppb |
2015-09-08 | 5100-001-0930 | 63.0 ppb |
2015-09-08 | 5100-008-1030 | 179.0 ppb |
2015-09-10 | 5100-017-0910 | 63.0 ppb |
2015-10-05 | 5100-001-0950 | 151.0 ppb |
2015-10-05 | 5100-008-0920 | 250.0 ppb |
2015-11-02 | 5100-001-0927 | 119.0 ppb |
2015-11-02 | 5100-008-0925 | 285.0 ppb |
2015-11-23 | 5100-017-1110 | 33.0 ppb |
2015-12-07 | 5100-001-0930 | 70.0 ppb |
2016-01-04 | 5100-001-0930 | 36.0 ppb |
2016-02-01 | 5100-001-1405 | 40.0 ppb |
2016-02-03 | 5100-012-1050 | ND |
2016-02-09 | 5100-005-0855 | ND |
2016-02-09 | 5100-011-0842 | 24.0 ppb |
2016-03-03 | 5100-006-1100 | ND |
2016-03-03 | 5100-017-0935 | 38.0 ppb |
2016-03-07 | 5100-001-0925 | 66.0 ppb |
2016-03-30 | 5100-020-1030 | 25.0 ppb |
2016-04-04 | 5100-005-1044 | ND |
2016-04-04 | 5100-008-0905 | 317.0 ppb |
2016-04-04 | 5100-013-1425 | 43.0 ppb |
2016-04-04 | 5100-019-1135 | ND |
2016-04-06 | 5100-012-1105 | 21.0 ppb |
2016-04-06 | 5100-020-1155 | 156.0 ppb |
2016-05-02 | 5100-019-1225 | 20.0 ppb |
2016-05-04 | 5100-001-0825 | 88.0 ppb |
2016-05-04 | 5100-008-1200 | 161.0 ppb |
2016-05-19 | 5100-007-0900 | ND |
2016-05-19 | 5100-017-0945 | 32.0 ppb |
2016-05-19 | 5100-020-1058 | 74.0 ppb |
2016-06-02 | 5100-005-0820 | ND |
2016-06-06 | 5100-001-0935 | 129.0 ppb |
2016-06-06 | 5100-008-1025 | 225.0 ppb |
2016-07-11 | 5100-001-0920 | 21.0 ppb |
2016-07-11 | 5100-008-1010 | 218.0 ppb |
2016-07-11 | 5100-020-1317 | 545.0 ppb |
2016-08-01 | 5100-001-1005 | 138.0 ppb |
2016-08-01 | 5100-008-0955 | 228.0 ppb |
2016-08-01 | 5100-020-1340 | 402.0 ppb |
2016-08-10 | 5100-005-1250 | 36.0 ppb |
2016-09-12 | 5100-001-0955 | 98.0 ppb |
2016-09-12 | 5100-008-1025 | 145.0 ppb |
2016-09-19 | 5100-007-1130 | 26.0 ppb |
2016-09-19 | 5100-017-1207 | 93.0 ppb |
2016-10-10 | 5100-001-0915 | 39.0 ppb |
2016-10-10 | 5100-008-0930 | 209.0 ppb |
2016-10-13 | 5100-012-1400 | 41.0 ppb |
2016-11-07 | 5100-001-1117 | 165.0 ppb |
2016-11-07 | 5100-008-1115 | 146.0 ppb |
2016-11-14 | 5100-017-1045 | 67.0 ppb |
2016-12-05 | 5100-001-0900 | 76.0 ppb |
2016-12-05 | 5100-008-0925 | 67.0 ppb |
2017-01-04 | 5100-013-1000 | 54.0 ppb |
2017-01-04 | 5100-017-0945 | 46.0 ppb |
2017-01-23 | 5100-008-0930 | 43.0 ppb |
2017-01-23 | 5100-012-1030 | 33.0 ppb |
2017-01-23 | 5100-020-1125 | 65.0 ppb |
2017-02-14 | 5100-008-1023 | 120.0 ppb |
2017-02-14 | 5100-020-1455 | 130.0 ppb |
2017-02-15 | 5100-001-1045 | 131.0 ppb |
2017-03-13 | 5100-001-0900 | 79.0 ppb |
2017-04-10 | 5100-001-0910 | 76.0 ppb |
2017-04-12 | 5100-017-1110 | 48.0 ppb |
2017-05-01 | 5100-001-0930 | 55.0 ppb |
2017-05-01 | 5100-008-1128 | 280.0 ppb |
2017-06-05 | 5100-001-0910 | 61.0 ppb |
2017-06-05 | 5100-006-1410 | 25.0 ppb |
2017-06-05 | 5100-007-1420 | 29.0 ppb |
2017-06-05 | 5100-008-1004 | 189.0 ppb |
2017-07-10 | 5100-007-1010 | ND |
2017-07-10 | 5100-019-1135 | ND |
2017-07-11 | 5100-001-0935 | 103.0 ppb |
2017-07-11 | 5100-008-0955 | 281.0 ppb |
2017-07-11 | 5100-017-1210 | 36.0 ppb |
2017-07-12 | 5100-012-0900 | 35.0 ppb |
2017-07-13 | 5100-013-0915 | 33.0 ppb |
2017-07-31 | 5100-020-1040 | 106.0 ppb |
2017-08-09 | 5100-001-1015 | 92.0 ppb |
2017-08-09 | 5100-008-1035 | 226.0 ppb |
2017-09-05 | 5100-001-0900 | 298.0 ppb |
2017-09-05 | 5100-008-0947 | 282.0 ppb |
2017-09-25 | 5100-005-1010 | 43.0 ppb |
2017-10-02 | 5100-001-0915 | 114.0 ppb |
2017-10-02 | 5100-008-1010 | 329.0 ppb |
2017-10-03 | 5100-005-1055 | 29.0 ppb |
2017-10-03 | 5100-013-1025 | 65.0 ppb |
2017-10-03 | 5100-017-0950 | 41.0 ppb |
2017-10-05 | 5100-006-0935 | 22.0 ppb |
2017-10-05 | 5100-007-1015 | ND |
2017-10-16 | 5100-019-1255 | 93.0 ppb |
2017-11-06 | 5100-001-0915 | 181.0 ppb |
2017-11-06 | 5100-008-1050 | 160.0 ppb |
2017-12-04 | 5100-001-0900 | 92.0 ppb |
2017-12-04 | 5100-008-0945 | 110.0 ppb |
2018-01-22 | 5100-001-0946 | 64.0 ppb |
2018-01-25 | 5100-005-1335 | 34.0 ppb |
2018-02-05 | 5100-012-0905 | 67.0 ppb |
2018-02-05 | 5100-013-0850 | 105.0 ppb |
2018-02-05 | 5100-017-0950 | 38.0 ppb |
2018-02-06 | 5100-001-0958 | 61.0 ppb |
2018-02-06 | 5100-005-0912 | 35.0 ppb |
2018-02-06 | 5100-011-0855 | 98.0 ppb |
2018-02-28 | 5100-006-0945 | 27.0 ppb |
2018-02-28 | 5100-008-1100 | 242.0 ppb |
2018-03-07 | 5100-001-1123 | 38.0 ppb |
2018-03-07 | 5100-008-1010 | 97.0 ppb |
2018-04-09 | 5100-001-1137 | 80.0 ppb |
2018-04-09 | 5100-008-1020 | 119.0 ppb |
2018-04-09 | 5100-017-1035 | 35.0 ppb |
2018-04-10 | 5100-005-1240 | 35.0 ppb |
2018-04-10 | 5100-011-1215 | 67.0 ppb |
2018-04-10 | 5100-019-0925 | 26.0 ppb |
2018-04-11 | 5100-006-1010 | 28.0 ppb |
2018-04-11 | 5100-012-1040 | 42.0 ppb |
2018-04-11 | 5100-013-0940 | 78.0 ppb |
2018-05-07 | 5100-001-1515 | 54.0 ppb |
2018-05-07 | 5100-008-1330 | 133.0 ppb |
2018-06-04 | 5100-001-0920 | 100.0 ppb |
2018-06-04 | 5100-008-1010 | 115.0 ppb |
2018-07-09 | 5100-001-1225 | 139.0 ppb |
2018-07-09 | 5100-005-1350 | 60.0 ppb |
2018-07-09 | 5100-008-0925 | 209.0 ppb |
2018-07-09 | 5100-013-0930 | 82.0 ppb |
2018-07-09 | 5100-017-1120 | 29.0 ppb |
2018-07-09 | 5100-019-1000 | 32.0 ppb |
2018-07-11 | 5100-006-0935 | 25.0 ppb |
2018-07-11 | 5100-011-0900 | 119.0 ppb |
2018-08-06 | 5100-001-0935 | 96.0 ppb |
2018-08-06 | 5100-008-0925 | 180.0 ppb |
2018-08-07 | 5100-007-0845 | 33.0 ppb |
2018-09-10 | 5100-001-0830 | 191.0 ppb |
2018-09-10 | 5100-008-0840 | 232.0 ppb |
2018-09-25 | 5100-020-1314 | 152.0 ppb |
2018-10-08 | 5100-001-0825 | 188.0 ppb |
2018-10-08 | 5100-008-0959 | 265.0 ppb |
2018-10-08 | 5100-012-1200 | 32.0 ppb |
2018-10-09 | 5100-017-0900 | 22.0 ppb |
2018-10-10 | 5100-007-1435 | 29.0 ppb |
2018-10-10 | 5100-020-1415 | 306.0 ppb |
2018-12-03 | 5100-008-1010 | 224.0 ppb |
2018-12-03 | 5100-020-1005 | 107.0 ppb |
2018-12-04 | 5100-013-0920 | 58.0 ppb |
2018-12-04 | 5100-019-1000 | 31.0 ppb |
2018-12-17 | 5100-001-0923 | 175.0 ppb |
2019-01-07 | 5100-005-1215 | 33.0 ppb |
2019-01-07 | 5100-008-1017 | 104.0 ppb |
2019-01-07 | 5100-012-1100 | 37.0 ppb |
2019-01-07 | 5100-017-1025 | 29.0 ppb |
2019-01-07 | 5100-020-1150 | 105.0 ppb |
2019-01-08 | 5100-007-0910 | 25.0 ppb |
2019-01-08 | 5100-011-1015 | 75.0 ppb |
2019-01-08 | 5100-019-0940 | 47.0 ppb |
2019-02-04 | 5100-008-1028 | 114.0 ppb |
2019-03-04 | 5100-008-0907 | 61.0 ppb |
2019-04-08 | 5100-007-1130 | 38.0 ppb |
2019-04-08 | 5100-008-0925 | 65.0 ppb |
2019-04-08 | 5100-017-0916 | 39.0 ppb |
2019-04-09 | 5100-006-0920 | 22.0 ppb |
2019-04-09 | 5100-012-0935 | 21.0 ppb |
2019-04-09 | 5100-013-0955 | 81.0 ppb |
2019-04-09 | 5100-019-1040 | 22.0 ppb |
2019-05-06 | 5100-001-0850 | 190.0 ppb |
2019-05-06 | 5100-008-1215 | 172.0 ppb |
2019-06-03 | 5100-001-0940 | 101.0 ppb |
2019-06-03 | 5100-008-0910 | 148.0 ppb |
2019-07-08 | 5100-005-1015 | 40.0 ppb |
2019-07-08 | 5100-007-0950 | 30.0 ppb |
2019-07-08 | 5100-011-0945 | 56.0 ppb |
2019-07-08 | 5100-013-1015 | 83.0 ppb |
2019-07-08 | 5100-020-1130 | 858.0 ppb |
2019-07-09 | 5100-006-1145 | ND |
2019-07-09 | 5100-017-0925 | ND |
2019-07-09 | 5100-019-1045 | 38.0 ppb |
2019-07-10 | 5100-001-1010 | 32.0 ppb |
2019-07-10 | 5100-008-1115 | 163.0 ppb |
2019-08-05 | 5100-001-1105 | 204.0 ppb |
2019-08-05 | 5100-008-0915 | 275.0 ppb |
2019-08-05 | 5100-012-0905 | ND |
2019-08-05 | 5100-020-0935 | 157.0 ppb |
2019-09-09 | 5100-001-0840 | 90.0 ppb |
2019-09-09 | 5100-008-1005 | 198.0 ppb |
2019-10-07 | 5100-001-1325 | 104.0 ppb |
2019-10-07 | 5100-008-1210 | 253.0 ppb |
2019-10-07 | 5100-020-0920 | 145.0 ppb |
2019-11-04 | 5100-001-0855 | 37.0 ppb |
2019-11-04 | 5100-008-1030 | 162.0 ppb |
2019-12-02 | 5100-008-1006 | 92.0 ppb |
2019-12-02 | 5100-020-0850 | 82.0 ppb |
2019-12-03 | 5100-017-1155 | 39.0 ppb |
2019-12-03 | 5100-019-1340 | 42.0 ppb |
2019-12-10 | 5100-017-1100 | 37.0 ppb |
2019-12-10 | 5100-019-0942 | 31.0 ppb |