EWG's Tap Water Database



Clearwater Water System

Uranium is a known human carcinogen. The federal legal limit for uranium is set at 30 micrograms per liter (corresponding to parts per billion), but utilities can also report uranium in picocuries per liter (pCi/L), which is a measure of radioactivity in water. EWG translated all uranium results to pCi/L using a conversion factor developed by the EPA. With this conversion approach, the limit of 30 ppb corresponds to 20 pCi/L. Drinking water with this much uranium would cause more than 4.6 cancer cases in a population of 100,000. California set a public health goal for uranium of 0.43 pCi/L. Read More.

Multiple forms of uranium can be detected in water, including uranium-234, uranium-235 and uranium-238. Uranium-234 is the most toxic form of uranium for human health.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
20100.13 pCi/L32ND - 0.20 pCi/L
20110.04 pCi/L31ND - 0.13 pCi/L
20120.18 pCi/L32ND - 0.34 pCi/L
20130.28 pCi/L330.11 pCi/L - 0.51 pCi/L
20140.09 pCi/L110.09 pCi/L
20150.07 pCi/L32ND - 0.16 pCi/L

pCi/L = picocuries per liter.

State and national drinking water standards and health guidelines

Health Guideline 0.43 pCi/L

The health guideline of 0.43 pCi/L for uranium 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. Three most common uranium isotopes are U-234, U-235 and U-238. All isotopes of uranium are radioactive, and the total radioactivity depends on the ratio of isotopes. This health guideline protects against cancer.

pCi/L = picocuries per liter.

EPA Maximum Contaminant
Level (MCL) 20 pCi/L

The enforceable federal standard that defines the highest level of a contaminant allowed in drinking water.

pCi/L = picocuries per liter.

All test results

Date Result
2010-02-100.19 pCi/L
2010-02-100.20 pCi/L
2011-02-160.13 pCi/L
2012-02-100.34 pCi/L
2012-02-100.21 pCi/L
2013-02-010.22 pCi/L
2013-02-010.51 pCi/L
2013-02-010.11 pCi/L
2014-02-130.09 pCi/L
2015-01-130.05 pCi/L
2015-01-130.16 pCi/L