EWG's Tap Water Database — 2021 UPDATE



Emma PWS

Chlorite is a disinfection byproduct resulting from water treatment with chlorine dioxide. Chlorite decreases hemoglobin levels and causes other hematologic effects. Read More.

Chlorite also forms when chlorine dioxide is used as a bleaching agent for textiles, paper pulp, flour and oils, and from the use of chlorine dioxide in food and packaging.� In 2009, California published a public health goal of 50 parts per billion for chlorite in drinking water. California state scientists reported that chlorite causes red blood cell damage, affects sperm and thyroid function, and may alter behavior and neurodevelopment of rat pups exposed in the womb.

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
2014338.4 ppb363651.0 ppb - 640.0 ppb
2015326.4 ppb3632ND - 590.0 ppb
2016402.3 ppb3331ND - 610.0 ppb
2017372.5 ppb393966.0 ppb - 530.0 ppb
2018505.2 ppb363637.0 ppb - 790.0 ppb
2019289.0 ppb333398.0 ppb - 500.0 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 50 ppb

The EWG Health Guideline of 50 ppb for chlorite 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 change in blood chemistry.

EPA Maximum Contaminant
Level (MCL) 1,000 ppb

ppb = parts per billion

All test results

Date Lab ID Result