EWG's Tap Water Database — 2021 UPDATE



Southwest Water Authority

Bromodichloromethane, one of the total trihalomethanes (TTHMs), is formed when chlorine or other disinfectants are used to treat drinking water. Bromodichloromethane and other disinfection byproducts increase the risk of cancer and may cause problems during pregnancy. Click here to read more about disinfection byproducts.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20141.11 ppb880.620 ppb - 2.60 ppb
20151.11 ppb880.780 ppb - 1.75 ppb
20161.26 ppb880.760 ppb - 1.78 ppb
20171.19 ppb880.930 ppb - 1.71 ppb
20183.67 ppb12121.09 ppb - 15.3 ppb
20191.44 ppb880.960 ppb - 2.47 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 0.06 ppb

The EWG Health Guideline of 0.06 ppb for bromodichloromethane was proposed in 2018 by the California Office of Environmental Health Hazard Assessment as a one-in-a-million lifetime risk of cancer. Values greater than one-in-a-million cancer risk level can result in increased cancer cases above one in a million people.

ppb = parts per billion

All test results

Date Lab ID Result
2014-02-1814-S1910.620 ppb
2014-02-1814-S1900.690 ppb
2014-05-2014-S8120.720 ppb
2014-05-2014-S8110.810 ppb
2014-08-1814-S19711.15 ppb
2014-08-1814-S19722.60 ppb
2014-11-1814-S27840.950 ppb
2014-11-1814-S27851.37 ppb
2015-02-1715-S1360.840 ppb
2015-02-1715-S1370.780 ppb
2015-05-1915-S7351.09 ppb
2015-05-1915-S7341.75 ppb
2015-08-1715-S16681.000 ppb
2015-08-1715-S16671.06 ppb
2015-11-1615-S24531.43 ppb
2015-11-1615-S24540.960 ppb
2016-02-1716-S1661.78 ppb
2016-02-1716-S1651.23 ppb
2016-05-1716-S9250.760 ppb
2016-05-1716-S9240.850 ppb
2016-08-2316-S21861.39 ppb
2016-08-2316-S21851.32 ppb
2016-11-1416-S27611.17 ppb
2016-11-1416-S27621.56 ppb
2017-02-2217-S2991.33 ppb
2017-02-2217-S2981.02 ppb
2017-05-1517-S7370.990 ppb
2017-05-1517-S7380.930 ppb
2017-08-2217-S17611.12 ppb
2017-08-2217-S17601.16 ppb
2017-11-1317-S24001.71 ppb
2017-11-1417-S24011.24 ppb
2018-02-1218-S2161.34 ppb
2018-02-1318-S2171.22 ppb
2018-05-1418-S6931.11 ppb
2018-05-1418-S6911.09 ppb
2018-08-2018-S17171.32 ppb
2018-08-2018-S17161.22 ppb
2018-10-2918-S230215.3 ppb
2018-11-1318-S237512.4 ppb
2018-11-1318-S23761.29 ppb
2018-12-0318-S24461.58 ppb
2018-12-1718-S25364.35 ppb
2018-12-1718-S25371.73 ppb
2019-02-1119-S1471.000 ppb
2019-02-1219-S1480.960 ppb
2019-05-1419-S6052.47 ppb
2019-05-1419-S6061.22 ppb
2019-08-1919-S17261.57 ppb
2019-08-2019-S17271.79 ppb
2019-11-1219-S24381.03 ppb
2019-11-1319-S24391.50 ppb