EWG's Tap Water Database — 2019 UPDATE



Status: No national drinking water standard exists


Radon is a radioactive gas that comes from soil and groundwater, and causes lung cancer. Highest exposures come from radon entering a house through its basement or crawl spaces, or from it volatilizing in the water. Read More.

Radon is the most common source of radiation exposure in the home. Radon in tap water is a smaller source of exposure compared to radon in indoor air. Water utilities report radon in picocuries per liter (pCi/L), which is a measure of radioactivity in water. The federal government has not set a Maximum Contaminant Level (MCL) for radon in tap water. In 1991, the EPA proposed a drinking water standard of 300 picocuries per liter for radon, which was not finalized. In 1999, the EPA proposed a combined approach for reducing radon risk in indoor air and limiting radon in drinking water. This approach recommended a maximum of 4,000 picocuries of radon per liter of drinking water in states with programs to address radon air risks. Where there was no state program for radon mitigation, a water radon limit of 300 picocuries per liter was to apply. This proposal has not yet become a federal law.

Click here to read more on radiological contaminants.

The draft federal limits for radon do not sufficiently protect public health. The EPA’s analysis on radon cancer risk suggests that for a water limit of 300 picocuries per liter, 200 in every 1 million people drinking water with this much radon could develop cancer over their lifetimes. For a water limit of 4000 picocuries per liter, over 2,000 people in every 1 million could develop cancer over their lifetimes. The EPA estimates that radon in drinking water causes about 168 cancer deaths per year – nearly 90 percent of which come from lung cancer caused by breathing radon released from water during showering or other water use. The remainder of cancer deaths are primarily from stomach cancer caused by consuming radon in water.




states detected


utilities detected

7.6 million

people served


states over health guideline


utilities over health guideline

7.6 million

people served over health guideline

Health concerns for radon

Lung cancer

Stomach cancer

State and national drinking water standards and health guidelines

EWG Health Guideline 1.5 pCi/L

The EWG Health Guideline of 1.5 pCi/L for radon was defined by the Environmental Protection Agency as a one-in-a-million lifetime risk of cancer. Values greater than one-in-a-million cancer risk level can result in increased cancer cases above one in a million people.

pCi/L = picocuries per liter

States reporting radon in drinking water

State UtilitiesPeople Served UtilitiesPeople Served
New York151,164,241151,164,241
North Carolina348,670348,670
Rhode Island448,199448,199
New Jersey114,000114,000
New Hampshire11081108

Filtering technologies that reduce radon

carbon filter icon

Activated Carbon

reverse osmosis icon

Reverse Osmosis

Utilities with the highest amounts of radon, 2012-2017

UtilityLocationTestsAverage levelPeople served
Staffordshire Country EstatesLeicester, MA19 of 2030,878.15 pCi/L140
Buffumville Heights Estates CondominiumOxford, MA17 of 1722,354.12 pCi/L40
East Ridge Mobile Home ParkWaldoboro, ME5 of 516,298.00 pCi/L100
Northeastern EstatesStandish, ME6 of 616,190.50 pCi/L40
Cherry Valley/ Rochdale Water DistrictLeicester, MA9 of 912,505.56 pCi/L3,255
Fcwwd #40/shaver SpringsFresno, CA2 of 212,440.00 pCi/L69
Pinewood On The Green CondosOxford, MA16 of 1811,714.44 pCi/L50
Colby WaterworksColby, WI1 of 110,819.00 pCi/L1,829
Northern Spring ParkPoland, ME7 of 79,535.57 pCi/L90
Harriman VillageHarriman, NY5 of 59,245.56 pCi/L5,000
Togus Pond Mobile Home ParkVentura, ME2 of 28,236.50 pCi/L53
Poland Place Condo AssociationPoland, ME5 of 68,029.17 pCi/L35
Rockwood MeadowsUpton, MA17 of 176,873.00 pCi/L124
Benchmark CondominiumsTyngsborough, MA12 of 186,700.00 pCi/L60
Charlton Manor Rest HomeCharlton, MA9 of 106,549.00 pCi/L26
Ayer Road Properties LLCHarvard, MA33 of 355,836.74 pCi/L150
Lamoille Water Users AssociationLamoille, NV4 of 45,200.20 pCi/L200
Estates At Highland RidgeHopkinton, MA11 of 114,790.91 pCi/L100
Chimera Inc.Narragansett, RI1 of 14,600.00 pCi/L155
Wiggin Farm WinterberryMerrimack, NH1 of 14,321.00 pCi/L108
Sunset Ridge CondominiumsBolton, MA6 of 94,320.00 pCi/L42
Bridgton Water DistrictBridgton, ME8 of 83,950.25 pCi/L2,053
Buena Vista ApartmentsLiberty, NY1 of 13,909.00 pCi/L52
Country View Holdings LlcSomerset, WI1 of 13,400.00 pCi/L75
Canton Water DistrictCanton, ME1 of 13,392.00 pCi/L293
Pinewood Acres Trailer ParkBowdoin, ME9 of 93,148.22 pCi/L63
Northbrook Village I / Berlin Ret.Berlin, MA1 of 13,080.00 pCi/L48
Winter Harbor Water DistrictWinter Harbor, ME7 of 72,897.57 pCi/L663
Belfast Cohousing & Ecovillage CondosBelfast, ME1 of 12,820.00 pCi/L90
Maine Water Company Kezar Falls DivisionSaco, ME1 of 12,760.00 pCi/L1,075
Charter Oak Mobile Home VillageFlagstaff, ME14 of 142,758.57 pCi/L105
Pilot Grove Apartments IIStow, MA2 of 22,685.00 pCi/L134
Gardiner Water DistrictGardiner, ME1 of 12,600.00 pCi/L8,000
Pawling Village*Pawling, NY4 of 42,495.00 pCi/L2,200
Pawling Water District #1Pawling, NY4 of 42,495.00 pCi/L100
Northbrook Village IIBerlin, MA1 of 12,440.00 pCi/L80
Regency At Stow CondominiumsStow, MA2 of 22,395.00 pCi/L132
Begin Trailer ParkSabattus, ME1 of 12,380.00 pCi/L170
Lynns WaySkowhegan, ME1 of 12,350.00 pCi/L33
Mount Rose Bowl Homeowners AssociationReno, NV1 of 12,307.20 pCi/L40
Howards Trailer ParkSwanville, ME5 of 62,201.17 pCi/L65
Century Mill EstatesBolton, MA3 of 32,100.00 pCi/L50
Clevengers VillageCulpeper, VA2 of 22,066.60 pCi/L855
Ladwp - Lone Pine*Bishop, CA1 of 12,000.00 pCi/L0
Inyo County Public Works Department - Lone PineIndependence, CA1 of 12,000.00 pCi/L2,035
Saint Josephs AbbeySpencer, MA1 of 12,000.00 pCi/L54
Ladwp - Big Pine*Bishop, CA3 of 31,900.00 pCi/L0
Big Pine Community Services DistrictBig Pine, CA3 of 31,900.00 pCi/L1,040
Holliston Water DepartmentHolliston, MA1 of 11,900.00 pCi/L14,946
Brook HollowPortland, ME7 of 71,888.43 pCi/L30

* This water utility supplies finished drinking water to at least one other water utility. The purchasing utility is not required to test for or report Radon, but it likely has the contaminant in its water supply.

UtilityLocationTestsAverage levelPeople served
Holliston Water DepartmentHolliston, MA1 of 11,900.00 pCi/L14,946
Marshfield UtilitiesMarshfield, WI1 of 11,700.00 pCi/L18,708
Elsinore Valley Municipal Water District*Lake Elsinore, CA2 of 21,700.00 pCi/L142,264
Maynard DPW, Water DivisionMaynard, MA6 of 81,373.75 pCi/L10,314
Westerly Water DepartmentWesterly, RI15 of 151,239.47 pCi/L38,000
Quakertown BoroQuakertown, PA15 of 281,022.13 pCi/L12,800
Sanford Water DistrictSanford, ME1 of 1930.00 pCi/L14,025
Greater Augusta Utility DistrictAugusta, ME4 of 4923.75 pCi/L14,380
Centennial Water and Sanitation District*Highlands Ranch, CO6 of 7874.57 pCi/L88,042
Eau Claire WaterworksEau Claire, WI2 of 2752.00 pCi/L66,060
Dayton Valley Water System*Dayton, NV5 of 5732.92 pCi/L14,168
Grafton Water District*Grafton, MA2 of 3643.33 pCi/L10,703
City of ElkoElko, NV7 of 7621.52 pCi/L18,000
City of TualatinTualatin, OR1 of 1601.00 pCi/L26,879
City of Santa Barbara Water Department*Santa Barbara, CA10 of 11566.36 pCi/L92,371
Elk Grove Water ServiceElk Grove, CA1 of 1543.00 pCi/L40,461
South Tahoe PUD - Main*South Lake Tahoe, CA66 of 67509.00 pCi/L29,500
Beverly Hills Water DepartmentBeverly Hills, CA4 of 4505.75 pCi/L44,290
Yorba Linda Water DistrictYorba Linda, CA3 of 3493.00 pCi/L77,513
City of Riverside*Riverside, CA5 of 5472.00 pCi/L303,871
Tualatin Valley Water DistrictBeaverton, OR1 of 1440.00 pCi/L206,600
City of Spokane*Spokane, WA5 of 5425.40 pCi/L227,505
City of Mesa*Mesa, AZ47 of 50385.22 pCi/L466,000
Cal American Water CompanyNewbury Park, CA98 of 108380.46 pCi/L61,206
Thousand Oaks Water DepartmentThousand Oaks, CA98 of 108380.46 pCi/L50,000
California Water Service Company - WestlakeSan Jose, CA98 of 108380.46 pCi/L19,451
Oak Park Water ServiceVentura, CA98 of 108380.46 pCi/L12,200
City of Fountain ValleyFountain Valley, CA3 of 3353.67 pCi/L56,464
City of Seal BeachSeal Beach, CA1 of 1334.00 pCi/L24,157
California Water Service (CWS) - SalinasSan Jose, CA1 of 1320.00 pCi/L106,858
City of AnaheimAnaheim, CA2 of 2311.00 pCi/L450,000
Elk RiverElk River, MN2 of 2294.00 pCi/L22,974
Fernley Public WorksFernley, NV2 of 2293.55 pCi/L18,000
Fond Du Lac WaterworksFond Du Lac, WI1 of 1240.40 pCi/L42,000
Redlands CityRedlands, CA1 of 1200.00 pCi/L80,000
City of AvondaleAvondale, AZ60 of 64175.07 pCi/L83,001
City of Napa*Napa, CA2 of 2167.50 pCi/L172,102
Irvine Ranch Water District*Irvine, CA5 of 12165.58 pCi/L370,000
Verona WaterworksVerona, WI1 of 1163.60 pCi/L10,619
Moore County Public Util. - Pinehurst*Carthage, NC7 of 9161.56 pCi/L19,368
Patuxent Naval Air Station (NAVFAC-WASH)Patuxent River, MD2 of 2158.80 pCi/L22,000
Big LakeBig Lake, MN2 of 2154.00 pCi/L10,060
Shrewsbury Water DepartmentShrewsbury, MA1 of 2125.00 pCi/L35,608
Madison Water Utility*Madison, WI1 of 1122.00 pCi/L235,000
City of Roseville*Roseville, CA2 of 2112.00 pCi/L119,000
Marin Municipal Water District*Corte Madera, CA5 of 6103.83 pCi/L195,362
Sacramento Suburban Water District*Sacramento, CA1 of 180.20 pCi/L171,200
Hoke County Regional Water SystemRaeford, NC5 of 878.01 pCi/L22,897
AlexandriaAlexandria, MN2 of 262.00 pCi/L12,415
Rockaway Twp Water DepartmentRockaway, NJ1 of 150.00 pCi/L14,000

* This water utility supplies finished drinking water to at least one other water utility. The purchasing utility is not required to test for or report Radon, but it likely has the contaminant in its water supply.