EWG's Tap Water Database — 2021 UPDATE



Nob Hill Water Association

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
20140.618 ppm54ND - 2.16 ppm
20150.238 ppm54ND - 0.530 ppm
20160.448 ppm54ND - 1.23 ppm
20170.336 ppm54ND - 0.550 ppm
20180.374 ppm54ND - 0.900 ppm
20190.292 ppm54ND - 0.560 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
2014-08-26213590.1000 ppm
2014-08-26213610.520 ppm
2014-08-26213620.310 ppm
2014-08-26213582.16 ppm
2015-08-04226950.260 ppm
2015-08-04226990.320 ppm
2015-08-04226960.0800 ppm
2015-08-04226980.530 ppm
2016-07-130.190 ppm
2016-07-130.320 ppm
2016-08-090.500 ppm
2016-08-091.23 ppm
2017-07-100.340 ppm
2017-07-100.540 ppm
2017-07-100.250 ppm
2017-07-100.550 ppm
2018-07-310.330 ppm
2018-07-310.120 ppm
2018-07-310.520 ppm
2018-07-310.900 ppm
2019-07-020.370 ppm
2019-07-020.440 ppm
2019-07-020.560 ppm
2019-07-020.0900 ppm