EWG's Tap Water Database — 2021 UPDATE


Monochloroacetic acid

Waltham Water Department (MWRA)

Monochloroacetic acid, one of the group of five haloacetic acids regulated by federal standards, is formed when chlorine or other disinfectants are used to treat drinking water. Haloacetic acids 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
20140.182 ppb242ND - 2.31 ppb
20150.275 ppb15218ND - 3.10 ppb
20160.139 ppb1288ND - 2.61 ppb
20170.372 ppb12820ND - 3.43 ppb
20182.45 ppb6551ND - 5.83 ppb
20191.73 ppb13281ND - 5.28 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 53 ppb

The EWG Health Guideline of 53 ppb for monochloroacetic acid was proposed in 2020 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 system toxicity.

ppb = parts per billion

All test results

Date Result