Maine well water by county: arsenic and nitrate
Modelled arsenic and nitrate for private-well users in every Maine county, what to test for, and where to find a certified lab. Private wells aren’t covered by the Safe Drinking Water Act.
All 16 counties
- York CountyWell users 61,700Arsenic about 25 in 100Nitrate 0.0 mg/L
- Penobscot CountyWell users 58,400Arsenic about 10 in 100Nitrate 0.0 mg/L
- Cumberland CountyWell users 53,500Arsenic about 26 in 100Nitrate 0.1 mg/L
- Kennebec CountyWell users 52,100Arsenic about 29 in 100Nitrate 0.1 mg/L
- Aroostook CountyWell users 36,100Arsenic about 16 in 100Nitrate 0.3 mg/L
- Hancock CountyWell users 35,600Arsenic about 22 in 100Nitrate 0.0 mg/L
- Oxford CountyWell users 32,900Arsenic about 6 in 100Nitrate 0.0 mg/L
- Androscoggin CountyWell users 31,000Arsenic about 44 in 100Nitrate 0.1 mg/L
- Somerset CountyWell users 26,200Arsenic about 22 in 100Nitrate 0.0 mg/L
- Waldo CountyWell users 25,500Arsenic about 12 in 100Nitrate 0.0 mg/L
- Lincoln CountyWell users 23,100Arsenic about 23 in 100Nitrate 0.1 mg/L
- Knox CountyWell users 18,300Arsenic about 12 in 100Nitrate 0.0 mg/L
- Washington CountyWell users 18,000Arsenic about 14 in 100Nitrate 0.0 mg/L
- Sagadahoc CountyWell users 15,400Arsenic about 41 in 100Nitrate 0.1 mg/L
- Franklin CountyWell users 13,000Arsenic about 14 in 100Nitrate 0.0 mg/L
- Piscataquis CountyWell users 9,300Arsenic about 15 in 100Nitrate 0.0 mg/L
Each mark = 1 in 100 well users the model places above 10 µg/L arsenic (scale 0–10)10 mg/L nitrate: the federal limit (MCL) for public systems
- These figures describe the area, not your well. Only a lab test shows what’s in your water.
- CDC says the Well Water Index figures “do not describe risk to individual wells.” (CDC Tracking Network)
- The arsenic model is better at spotting low-arsenic areas than at confirming high ones.
- Well-user counts are 2010 USGS estimates; tract values are averages over each census tract.
- Total coliform bacteriaEvery year
- NitrateEvery year
- Total dissolved solidsEvery year
- pHEvery year
- ArsenicAsk your local health department
EPA: Private Drinking Water Wells · CDC: Guidelines for Testing Well Water
Use a state-certified lab
Maine Department of Health & Human Services lists the laboratories certified to test drinking water in Maine.
Screening tells you if something is worth a closer look
A lab result is the number you can act on.
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Lab-certified results
ETR Labs Basic Water Quality Test Kit
ETR Laboratories
50+ substances, including lead, copper, arsenic, nitrate, hardness and coliform bacteria
- Analyzed by Environmental Testing and Research Laboratories (ETR Labs), Leominster, MA · ISO/IEC 17025:2017, ANAB certificate AT-2638
- Turnaround: 2–4 business days after the lab receives it
What it can't tell you: It does not test PFAS, and not every result on the panel falls under the lab's accredited scope.
Screening: quick check, not lab-grade
Watersafe Drinking Water Test Kit
Silver Lake Research
Lead, bacteria, nitrate, copper, iron, chlorine, hardness and pH
- Turnaround: Minutes; the bacteria test can take up to 48 hours
What it can't tell you: Each test gives a yes/no or a rough range, not a lab number, and it cannot detect PFAS or arsenic.
A mail-in kit’s lab is accredited (ISO/IEC 17025) but may not be certified by your state. For a home sale, a loan, or a health-department follow-up, use a state-certified lab.
Maine well water
Sources: CDC Well Water Index (2024) · USGS arsenic and nitrate models · USGS domestic well populations · EPA and CDC testing guidance. Data last updated 2026-10-08. All sources →
How many people use private wells in Maine?
About 510,200 people across 16 Maine counties, by the USGS 2010 estimate. USGS models place about 108,300 of them in areas where wells are likely to be above the 10 µg/L arsenic limit. These are area estimates, not well results.
Are private wells regulated in Maine?
The quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments and laws. (EPA) Testing and treatment are the owner's responsibility.
Where can I get my well tested in Maine?
Maine Department of Health & Human Services keeps the list of laboratories certified to test drinking water in Maine. Only use laboratories that are certified to do drinking water testing. (EPA)