Well water in Maine: testing, risks and accredited labs by county

Many Maine residents get their drinking water from a private well. Private wells aren't covered by federal drinking water rules, so owners are responsible for testing their own water.

Source: Testing your well water

Counties

Androscoggin County
Arsenic
About 9,700 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 7,600 to 12,300).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Aroostook County
Arsenic
About 9,500 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 7,700 to 11,400).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Cumberland County
Arsenic
About 6,000 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 4,500 to 7,800).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Franklin County
Arsenic
About 2,200 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 1,600 to 2,800).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Hancock County
Arsenic
About 4,200 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 3,000 to 6,000).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Kennebec County
Arsenic
About 15,300 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 12,200 to 18,700).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Knox County
Arsenic
About 1,000 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 700 to 1,400).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: Moderate
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Lincoln County
Arsenic
About 1,900 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 1,400 to 2,600).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Oxford County
Arsenic
About 6,200 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 4,700 to 8,100).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Penobscot County
Arsenic
About 18,700 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 15,600 to 22,000).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Piscataquis County
Arsenic
About 1,100 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 900 to 1,400).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Sagadahoc County
Arsenic
About 1,100 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 800 to 1,400).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: Moderate
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Somerset County
Arsenic
About 7,200 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 5,900 to 8,800).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Waldo County
Arsenic
About 5,100 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 4,000 to 6,400).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: Moderate
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
Washington County
Arsenic
About 2,800 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 2,000 to 3,800).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: Moderate
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.
York County
Arsenic
About 10,400 people on private wells may have arsenic above the drinking water limit of 10 micrograms per liter (likely 7,700 to 13,700).
USGS estimate based on 2010 population, published 2017.
Maine advises well owners to compare their results to this limit.
Radon
Indoor radon potential: High
EPA zone for indoor air. It doesn't measure your well water.
Private-well labs
Accredited labs are listed statewide. Most accept mail-in samples.

Tribal Public Health District

Joshua Toner, Tribal Public Health District Liaison

207-532-4273 Ext: 227

What to test for

Maine's uniform recommended tests for private wells

10-144 CMR chapter 257 lists these tests for residential private wells. RES1 is the uniform testing recommendation compliant post-1988. The rule adds first draw lead for the package it calls the uniform testing recommendation compliant pre-1988. It does not define pre-1988 by home or plumbing age, and it does not say how often to test.

coliform bacteria & E. coli (pos/neg)
radon water
nitrate
nitrite
fluoride
chloride
sodium
hardness
copper
iron
pH
manganese
uranium
lead
arsenic
magnesium
first draw lead (uniform testing recommendation compliant pre-1988)

Source: Maine Department of Health and Human Services, 10-144 CMR Chapter 257, Health and Environmental Testing Laboratory Fee Schedule

How often to test (Maine CDC)

Test	How often
Coliform bacteria, E. coli, and nitrates and nitrites	Every year
Arsenic, chloride, copper, fluoride, hardness, iron, lead, magnesium, manganese, pH, radon, sodium, and uranium	Every 3 to 5 years

Other times to test

If you have never tested your well, do a comprehensive or standard test for everything listed above.
If you are expecting a baby
Your water changes in smell, taste, and color
Your well runs dry and comes back
When buying a new home
After installing a water treatment system or replacing parts of your treatment system
After any work is done on your well

Source: Maine Center for Disease Control and Prevention, Testing your well water

Maine law (22 MRS §2660-T) also names PFAS among recommended private well tests.

Source: Maine Legislature, 22 MRS §2660-T, Uniform private well testing recommendations

Questions about what to test for or what your results mean? Contact the Maine CDC Toxicology Team at (207) 287-4311 or [email protected].

Source: Maine Center for Disease Control and Prevention, Private Well Water

Sources

Estimated county-level domestic well population with arsenic greater than 10 micrograms per literU.S. Geological Survey, 2017
EPA Map of Radon ZonesU.S. Environmental Protection Agency, 1993
10-144 CMR Chapter 257, Health and Environmental Testing Laboratory Fee ScheduleMaine Department of Health and Human Services, 2020
22 MRS §2660-T, Uniform private well testing recommendationsMaine Legislature, 2025
Testing your well waterMaine Center for Disease Control and Prevention
Maine In-State Commercial Drinking Water LabsMaine Drinking Water Program, 2026
Accredited Laboratories in MaineMaine Center for Disease Control and Prevention, 2026
All laboratories accredited by MaineMaine Drinking Water Program, 2026
Maine public health districtsMaine Center for Disease Control and Prevention
2026 Gazetteer file for Maine county subdivisionsU.S. Census Bureau, 2026
30-A MRS §2001, municipalityMaine Legislature, 1989
Private Well WaterMaine Center for Disease Control and Prevention