EWG's Tap Water Database — 2019 UPDATE


Nitrate and nitrite

Duncan Public Utilities Authority

Nitrate and nitrite enter water from fertilizer runoff, septic tanks and urban runoff. These contaminants can cause oxygen deprivation for infants and increase the risk of cancer. Nitrite is significantly more toxic than nitrate. 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
20130.350 ppm110.350 ppm
20140.1000 ppm110.1000 ppm
20150.200 ppm110.200 ppm
20160.300 ppm110.300 ppm
20170.150 ppm110.150 ppm

ppm = parts per million

State and national drinking water standards and health guidelines

EWG Health Guideline 0.14 ppm

The health guideline of 0.14 parts per million, or ppm, for nitrate and nitrite is based on the equivalent health guideline for nitrate, as defined in a peer-reviewed scientific study by EWG. This guideline represents a one-in-one-million annual cancer risk level.

EPA Maximum Contaminant
Level (MCL) 10 ppm

ppm = parts per million

All test results

Date Lab ID Result
2013-03-12025314.0010.350 ppm
2014-03-10040129.0010.1000 ppm
2015-02-11053456.0010.200 ppm
2016-03-22SDWA-1015051-000.300 ppm
2017-03-02SDWA-1116278-000.150 ppm