EWG's Tap Water Database — 2021 UPDATE



West Delta Water Supply Corporation

Nitrate, a fertilizer chemical, frequently contaminates drinking water due to agricultural and urban runoff, and discharges from municipal wastewater treatment plants and septic tanks. Excessive nitrate in water can cause oxygen deprivation in infants and increase the risk of cancer. Click here to read more about nitrate.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20140.122 ppm220.0505 ppm - 0.193 ppm
20150.223 ppm220.0675 ppm - 0.378 ppm
20161.84 ppm220.0670 ppm - 3.61 ppm
20170.236 ppm220.0845 ppm - 0.388 ppm
20180.111 ppm220.0636 ppm - 0.158 ppm
20190.0642 ppm220.0623 ppm - 0.0660 ppm

ppm = parts per million

State and national drinking water standards and health guidelines

EWG Health Guideline 0.14 ppm

The EWG Health Guideline of 0.14 ppm for nitrate was defined by EWG . This health guideline protects against cancer and harm to fetal growth and development.

EPA Maximum Contaminant
Level (MCL) 10 ppm

The legal limit for nitrate, established in 1962, was developed to protect infants from acute methemoglobinemia, a life-threatening disorder of oxygen transport in the body. This limit does not fully protect against the risk of cancer and harm to the developing fetus.

ppm = parts per million

All test results

Date Lab ID Result
2014-09-24Q14476540010.193 ppm
2014-12-08Q14588490020.0505 ppm
2015-10-15Q15404660010.0675 ppm
2015-10-15Q15404660020.378 ppm
2016-06-09Q16233030040.0670 ppm
2016-06-09Q16233030053.61 ppm
2017-08-22Q17375090010.388 ppm
2017-08-22Q17375090060.0845 ppm
2018-06-21Q18248810050.0636 ppm
2018-06-21Q18248810130.158 ppm
2019-08-26Q19594540040.0623 ppm
2019-08-26Q19594540050.0660 ppm