EWG's Tap Water Database — 2019 UPDATE


N-Nitrosodimethylamine (NDMA)

California Water Service Company - Hermosa / Redondo Beach

N-Nitrosodimethylamine is one of the DNA-damaging, cancer-causing contaminants called N-nitrosamines that can form during water treatment with the use of certain disinfectants, such as chloramine. Read More.

Pollution of water sources with effluent from municipal wastewater treatment plants and runoff from animal feeding operations contributes to nitrosamine formation. Fifteen different nitrosamines are listed as carcinogens in the U.S. Department of Health and Human Services National Toxicology Program Report on Carcinogens. The federal government has not set a legal limit for nitrosamines in drinking water and water utilities typically do not test for these contaminants. California has set a public health goal for one of the most common nitrosamines, N-nitrosodimethylamine or NDMA, at 0.003 parts per billion in drinking water, a concentration that corresponds to an estimated one-in-one-million cancer risk.

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
20122.63 ppt86ND - 8.00 ppt
20132.13 ppt86ND - 4.00 ppt
20141.75 ppt85ND - 4.00 ppt
20152.64 ppt86ND - 3.80 ppt
20162.55 ppt87ND - 4.10 ppt
20172.60 ppt882.00 ppt - 3.40 ppt

ppt = parts per trillion

State and national drinking water standards and health guidelines

EWG Health Guideline 3 ppt

The EWG Health Guideline of 3 ppt for n-nitrosodimethylamine was defined by the California Office of Environmental Health Hazard Assessment as a public health goal, the level of a drinking water contaminant that does not pose a significant health risk. This health guideline protects against cancer.

ppt = parts per trillion

All test results

Date Lab ID Result
2012-02-229590-011-11053.00 ppt
2012-02-229590-008-08408.00 ppt
2012-05-169590-008-09003.00 ppt
2012-05-169590-011-11203.00 ppt
2012-08-169590-008-12002.00 ppt
2012-08-169590-011-12532.00 ppt
2013-02-209590-011-12102.00 ppt
2013-05-159590-011-09182.00 ppt
2013-08-149590-008-08453.00 ppt
2013-08-149590-011-09304.00 ppt
2013-11-139590-008-08353.00 ppt
2013-11-139590-011-11203.00 ppt
2014-02-199590-008-09503.00 ppt
2014-02-199590-011-12303.00 ppt
2014-05-219590-011-11452.00 ppt
2014-05-219590-008-09202.00 ppt
2014-08-079590-008-09124.00 ppt
2015-05-069590-008-10053.00 ppt
2015-05-069590-011-11003.00 ppt
2015-08-049590-008-08483.80 ppt
2015-08-049590-011-14093.80 ppt
2015-11-039590-011-14193.70 ppt
2015-11-039590-008-08513.80 ppt
2016-02-039590-008-13002.10 ppt
2016-05-059590-011-13302.20 ppt
2016-05-059590-008-11002.80 ppt
2016-08-109590-011-10252.40 ppt
2016-08-109590-008-12353.20 ppt
2016-11-099590-008-08434.10 ppt
2016-11-099590-011-09253.60 ppt
2017-02-099590-008-10513.40 ppt
2017-02-099590-011-14523.40 ppt
2017-05-039590-011-12552.00 ppt
2017-05-039590-008-08502.10 ppt
2017-08-229590-008-08302.40 ppt
2017-08-229590-011-14352.00 ppt
2017-11-089590-008-14403.30 ppt
2017-11-089590-011-13302.20 ppt