The Power of Information

National Drinking Water Database


Radon in California


Radon is a radioactive breakdown product of radium and uranium in soil, rock and water; it is often present in groundwater. [read more]

The Most Polluted Communities in California

79 water utilities reported detecting Radon in tap water since 2004, according to EWG's analysis of water quality data supplied by state water agencies

Ranked by highest average Radon level

RankSystem Population Served Positive test results of total reported tests Average Level
(Range)
1Bass Lake Water Company
Bass Lake, CA
3,0061 of 119915 pCi/L
(19915 pCi/L)
2Cws Mtn. Shadows Water System
Wofford Heights, CA
1953 of 36499.33 pCi/L
(5735 to 6990 pCi/L)
3Kirkwood Meadows Pubilc Utilit
Kirkwood, CA
1502 of 22815 pCi/L
(1730 to 3900 pCi/L)
4South Tahoe Pud - Main
South Lake Tahoe, CA
60,00020 of 201976.58 pCi/L
(309 to 4916 pCi/L)
5Cdf - Owens Valley Conservation Corp
Bishop, CA
2501 of 11502 pCi/L
(1502 pCi/L)
6Tahoe Keys Water Company
South Lake Tahoe, CA
3,0041 of 11306.67 pCi/L
(1306.67 pCi/L)
7Cws - Visalia
Visalia, CA
87,7601 of 1812 pCi/L
(812 pCi/L)
8City of Stockton
Stockton, CA
155,1931 of 1625 pCi/L
(625 pCi/L)
9Redlands City Mud-Water Div
Redlands, CA
69,30069 of 72596.5 pCi/L
(0 to 2300 pCi/L)
10Golden State WC - Placentia
Placentia, CA
36,3743 of 3567 pCi/L
(512 to 624 pCi/L)

Health Based Limits for Radon

StandardDescriptionLevel
One in one million (10-6) Cancer RiskThe concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 1,000,000. Source: U.S. Environmental Protection Agency.1.5 pCi/L
One in ten thousand (10-4) Cancer RiskThe concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 10,000. Source: U.S. Environmental Protection Agency.150 pCi/L

Violation Summary for Radon in California

There are no violations reported for this contaminant in California