EWG's Tap Water Database — 2019 UPDATE



Williams Water Supply

Chloromethane is an industrial solvent, aerosol propellant and a refrigerant. It also forms as a byproduct of water disinfection. The EPA classifies chloromethane as possibly carcinogenic to humans.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20122.90 ppb332.50 ppb - 3.70 ppb
20132.23 ppb331.80 ppb - 2.60 ppb
20143.18 ppb441.50 ppb - 4.10 ppb
20152.78 ppb441.60 ppb - 3.90 ppb
20162.98 ppb442.50 ppb - 3.50 ppb
20173.60 ppb442.50 ppb - 5.00 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 2.69 ppb

The EWG Health Guideline of 2.69 ppb for chloromethane was defined by the Environmental Protection Agency as a benchmark for testing under the Unregulated Contaminant Monitoring Rule program. This health guideline protects against cancer.

ppb = parts per billion

All test results

Date Lab ID Result
2012-05-0819023202.50 ppb
2012-08-1319240223.70 ppb
2012-10-0219366632.50 ppb
2013-01-2119586412.30 ppb
2013-04-0319702321.80 ppb
2013-11-1220183022.60 ppb
2014-02-1020344711.50 ppb
2014-05-0520499904.10 ppb
2014-08-0420690513.70 ppb
2014-11-1020922503.40 ppb
2015-02-04OE2129911.60 ppb
2015-05-04OE2389353.90 ppb
2015-08-05OE2770663.70 ppb
2015-11-09OE3161601.90 ppb
2016-02-01OE3421772.50 ppb
2016-05-04OE3745402.70 ppb
2016-08-08OE4129853.50 ppb
2016-11-02OE4486473.20 ppb
2017-02-01OE4770122.50 ppb
2017-08-02OE5458015.00 ppb
2017-10-10OE5775742.70 ppb
2017-11-09OE5888684.20 ppb