EWG's Tap Water Database — 2019 UPDATE



Northwest Utilities

Selenium is an essential element in diets. But too much selenium can decrease thyroid hormone production and cause hair loss, skin lesions and brittle fingernails.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20122.03 ppb330.900 ppb - 3.10 ppb
20130.267 ppb31ND - 0.800 ppb
20140.633 ppb330.500 ppb - 0.700 ppb
20150.633 ppb330.600 ppb - 0.700 ppb
20160.167 ppb31ND - 0.500 ppb
20171.57 ppb331.40 ppb - 1.80 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

EWG Health Guideline 30 ppb

The EWG Health Guideline of 30 ppb for selenium was defined by the California Office of Environmental Health Hazard Assessment as a public health goal, the level of a drinking water contaminant that does not pose a significant health risk. This health guideline protects against hair loss and nail damage.

EPA Maximum Contaminant
Level (MCL) 50 ppb

The legal limit for selenium, established in 1991, was based on human epidemiological studies of populations exposed to naturally occurring selenium in drinking water. This limit does not include any additional consideration of children’s health.

ppb = parts per billion

All test results

Date Result
2012-08-220.900 ppb
2012-09-042.10 ppb
2012-09-043.10 ppb
2013-08-130.800 ppb
2014-07-210.500 ppb
2014-07-210.700 ppb
2014-07-210.700 ppb
2015-09-150.600 ppb
2015-09-150.700 ppb
2015-09-150.600 ppb
2016-09-120.500 ppb
2017-08-231.80 ppb
2017-08-231.40 ppb
2017-08-231.50 ppb