EWG's Tap Water Database — 2021 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

5.9 million

people served


states over health guideline


utilities over health guideline

5.9 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 York151,160,892171,161,882
Rhode Island348,132348,132
New Jersey114,000114,000
New Hampshire145,575145,575
West Virginia21,94321,943

Filtering technologies that reduce radon

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Activated Carbon

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Reverse Osmosis

Utilities with the highest amounts of radon, 2014-2019

UtilityLocationTestsAverage levelPeople served
Staffordshire Country EstatesLeicester, MA21 of 2228,598.95 pCi/L140
Spinsfield CommonsFranklin, ME1 of 119,200.00 pCi/L45
East Ridge Mobile Home ParkWaldoboro, ME14 of 1419,182.86 pCi/L63
Buffumville Heights Estates CondominiumOxford, MA25 of 2517,702.40 pCi/L40
White Mountain Resort/gatewayMoultonborough, NH1 of 114,000.00 pCi/L208
Northeastern EstatesStandish, ME7 of 713,961.86 pCi/L40
Cherry Valley/ Rochdale Water DistrictLeicester, MA6 of 613,181.67 pCi/L3,337
Pinewood On The Green CondosOxford, MA15 of 1812,760.00 pCi/L50
Fcwwd #40/shaver SpringsFresno, CA2 of 212,440.00 pCi/L69
BrandywineEpping, NH1 of 112,200.00 pCi/L72
Harriman VillageHarriman, NY4 of 411,439.45 pCi/L5,000
Colby WaterworksColby, WI1 of 110,819.00 pCi/L1,829
Charlton Manor Rest HomeCharlton, MA11 of 1110,204.55 pCi/L26
Countryside ApartmentsHollis, ME3 of 58,298.80 pCi/L32
Benchmark CondominiumsTyngsborough, MA12 of 186,346.67 pCi/L60
Rockwood MeadowsUpton, MA23 of 236,115.57 pCi/L80
Poland Place Condo AssociationPoland, ME5 of 86,021.88 pCi/L35
Togus Pond Mobile Home ParkVentura, ME8 of 85,836.50 pCi/L53
Saco River ApartmentsHollis, ME4 of 45,603.50 pCi/L30
Ayer Road Properties LLCHarvard, MA33 of 355,557.60 pCi/L150
Lamoille Water Users AssociationLamoille, NV4 of 45,200.20 pCi/L200
Chimera Inc.Narragansett, RI1 of 14,600.00 pCi/L133
Wiggin Farm WinterberryMerrimack, NH1 of 14,321.00 pCi/L108
Oliverian SchHaverhill, NH1 of 14,208.00 pCi/L76
Buena Vista ApartmentsLiberty, NY1 of 13,909.00 pCi/L52
Brook HollowPortland, ME6 of 73,873.29 pCi/L30
Bridgton Water DistrictBridgton, ME14 of 143,636.29 pCi/L2,283
Estates At Highland RidgeHopkinton, MA13 of 133,437.69 pCi/L100
Country View Holdings LlcSomerset, WI1 of 13,400.00 pCi/L75
Sunrise Hill EstatesBarrington, ME1 of 13,180.00 pCi/L100
Northbrook Village I / Berlin Ret.Berlin, MA1 of 13,080.00 pCi/L48
Leicester Water Supply District*Leicester, MA4 of 62,764.57 pCi/L3,200
Maine Water Company Kezar Falls DivisionSaco, ME1 of 12,760.00 pCi/L993
Fields At Sherborn Condo TrustSherborn, MA2 of 22,700.00 pCi/L110
Canton Point ParkHartford, ME6 of 62,656.82 pCi/L88
Pawling Water District #1Pawling, NY4 of 42,495.00 pCi/L100
Pawling Village*Pawling, NY4 of 42,495.00 pCi/L2,200
Old Coach VillageDerry, NH4 of 42,447.50 pCi/L50
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/L40
Sunset Ridge CondominiumsBolton, MA6 of 102,314.00 pCi/L42
Mount Rose Bowl Property Owners Water Co.Reno, NV1 of 12,307.20 pCi/L40
Four Winds Homeowners AssociationSouth Thomaston, ME1 of 12,238.00 pCi/L43
Pilot Grove Apartments IIStow, MA1 of 12,220.00 pCi/L134
Stratham WoodsStratham, NH1 of 12,153.00 pCi/L38
Quakertown BoroQuakertown, PA14 of 142,043.50 pCi/L12,800
Freedom Village CondosNashua, NH1 of 12,043.00 pCi/L165
Charter Oaks Village CooperativeWaldoboro, ME22 of 232,024.57 pCi/L105

* 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
Quakertown BoroQuakertown, PA14 of 142,043.50 pCi/L12,800
Holliston Water DepartmentHolliston, MA1 of 11,900.00 pCi/L14,946
Carson City Public Works*Carson City, NV2 of 21,590.00 pCi/L56,000
Maynard DPW, Water DivisionMaynard, MA6 of 81,373.75 pCi/L10,665
Westerly Water DepartmentWesterly, RI15 of 151,239.47 pCi/L38,000
Elsinore Valley Municipal Water District*Lake Elsinore, CA15 of 15948.47 pCi/L142,264
Sanford Water DistrictSanford, ME1 of 1930.00 pCi/L14,025
Beverly Hills Water DepartmentBeverly Hills, CA8 of 8874.13 pCi/L44,290
Greater Augusta Utility DistrictAugusta, ME2 of 2859.00 pCi/L15,040
Eau Claire WaterworksEau Claire, WI2 of 2752.00 pCi/L66,060
South Tahoe PUD - Main*South Lake Tahoe, CA62 of 62725.24 pCi/L29,500
Dayton Valley Water System*Dayton, NV7 of 7716.36 pCi/L15,830
City of ElkoElko, NV7 of 7621.52 pCi/L20,451
City of TualatinTualatin, OR1 of 1601.00 pCi/L26,879
City of Santa Barbara Water Department*Santa Barbara, CA1 of 1470.00 pCi/L92,371
City of Riverside*Riverside, CA3 of 3460.00 pCi/L303,871
Tualatin Valley Water District*Beaverton, OR1 of 1440.00 pCi/L222,000
City of Spokane*Spokane, WA10 of 10411.70 pCi/L227,509
Oak Park Water ServiceVentura, CA97 of 118377.31 pCi/L12,200
Cal American Water CompanyNewbury Park, CA97 of 118377.31 pCi/L61,206
Thousand Oaks Water DepartmentThousand Oaks, CA97 of 118377.31 pCi/L50,000
California Water Service Company - WestlakeSan Jose, CA97 of 118377.31 pCi/L19,451
Fernley Public WorksFernely, NV1 of 1369.00 pCi/L19,790
California Water Service (CWS) - SalinasSan Jose, CA1 of 1320.00 pCi/L106,858
Fond Du Lac WaterworksFond Du Lac, WI1 of 1240.40 pCi/L42,000
City of Mesa*Mesa, AZ2 of 2230.50 pCi/L466,000
Virgin Valley Water DistrictMesquite, NV2 of 2185.40 pCi/L18,000
Coachella Valley Water District: Cove Community*Palm Desert, CA2 of 2184.50 pCi/L198,544
City of AvondaleAvondale, AZ17 of 18178.36 pCi/L83,001
Platteville WaterworksPlatteville, WI1 of 1159.50 pCi/L12,268
Patuxent Naval Air Station (NAVFAC-WASH)Patuxent River, MD2 of 2158.80 pCi/L22,000
Madison Water Utility*Madison, WI1 of 1122.00 pCi/L235,000
City of WestminsterWestminster, MD1 of 2109.05 pCi/L35,256
Sussex Village Hall & Water UtilitySussex, WI1 of 199.20 pCi/L10,573
Marin Municipal Water District*Corte Madera, CA5 of 697.63 pCi/L195,362
Independence*Independence, MO2 of 277.35 pCi/L117,240
Rockaway Twp Water DepartmentRockaway, NJ1 of 150.00 pCi/L14,000
St James WDSt James, NY4 of 421.62 pCi/L10,587
Smithtown WDKings Park, NY4 of 421.62 pCi/L19,635
Suffolk County Water Authority*Bayshore, NY4 of 421.62 pCi/L1,100,000

* 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.