EWG's Tap Water Database — 2021 UPDATE


Nitrate and nitrite

Southwest Water 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
20140.0900 ppm110.0900 ppm
20150.120 ppm110.120 ppm
20160.0400 ppm110.0400 ppm
20170.0500 ppm110.0500 ppm
20180.0875 ppm440.0600 ppm - 0.120 ppm
20190.0810 ppm110.0810 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
2014-04-0714-S5810.0900 ppm
2015-06-0315-S8400.120 ppm
2016-05-1116-S8560.0400 ppm
2017-05-2317-S8040.0500 ppm
2018-02-2818-S2980.0900 ppm
2018-02-2818-S3000.0800 ppm
2018-02-2818-S2990.0600 ppm
2018-05-1518-S7210.120 ppm
2019-05-1419-S6370.0810 ppm