Well Water Notebook
Information only, not medical advice. We never say whether your water is safe to drink. Ask a state-certified lab or your local health department. Disclaimer

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Well water testing in Penobscot County, Maine

About half of Maine residents use private wells. Arsenic, uranium and radon are the big naturally occurring concerns. Here's what Maine CDC recommends, who gives free help, and where to get a sample analyzed in or near Penobscot County, with a source for every fact.

This page can't tell you whether your water is safe to drink. Maine CDC says the only way to know is to test it.2 For help with results, call Maine CDC's well water line (below).

How many people here use a private well

USGS estimates that about 81,000 people in Penobscot County supplied their own household water in 2015, about 53% of the county's population.1 Statewide, USGS estimated about 50% of Maine residents supplied their own water in 2015, the highest share of any state.1 Maine CDC says more than half of people in Maine get their drinking water from a private well.3

Are private wells regulated in Maine?

No. Maine CDC says private wells aren't regulated, and property owners are responsible for testing and treating their well water.2

Arsenic, uranium and radon

That's about three times the model's estimate for Cumberland County, even though more people in Cumberland County use private wells.51

Town-level results: the MaineTracking Network private well page summarizes thousands of samples tested at the state lab by town and county, for arsenic, fluoride, manganese, nitrate, nitrite and uranium.6 The Tracking Network cautions that the data come only from the state lab and from owners who chose to test, so hot-spot areas may look worse than average.6 We didn't publish county percentages here because we couldn't export them from the state's dashboard to check them.

What to test and how often

Maine CDC recommends:2

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

If you've never tested, Maine CDC recommends a comprehensive or standard test for everything above. It also suggests testing if you're expecting a baby, if the water changes in smell, taste or color, if the well runs dry and comes back, when buying a home, after installing or servicing treatment, and after any work on the well.2

Where to get tested and treatment options

State lab kits. Maine's Health and Environmental Testing Laboratory (HETL) offers private-well test kits, including a bacteria and nitrate/nitrite "Basic Safety" kit, a "Well Evaluation" kit it recommends every 5 years, a "Residential Sales" kit, and "Res 1" and "Res 2" kits that add radon in water (and, for Res 2, first-draw lead).7 Any of HETL's methods can also be ordered à la carte.7

Accredited labs. Maine CDC's list of in-state commercial drinking water labs (updated 5/16/2026) includes these in or near Penobscot County:8

Lab City Phone
ClearWater Laboratory (a division of Acheron Engineering) Newport (207) 368-5786
NELAnalytical (previously Northeast Laboratory Services) Winslow (207) 873-7711
Health and Environmental Testing Laboratory (HETL, state lab) Augusta (207) 287-2727

Maine accredits labs test by test, so ask each lab whether it's accredited for what you need. Questions about lab quality go to the Maine Drinking Water Program at 207-287-2070 (ask for the Laboratory Accreditation Officer).8 For radon in water, Maine CDC keeps a separate list of radon labs.2

If a result is high. Maine CDC's Quick Guide to Well Water Treatment matches each contaminant to treatment types. For example, it lists adsorptive media, reverse osmosis or anion exchange for arsenic; reverse osmosis for uranium (noting there's no NSF-certified method to remove uranium); and adsorptive media or aeration for radon.3 If your arsenic result is above 100 µg/L, Maine CDC asks you to call before choosing treatment.3 See arsenic, uranium and radon, and whole-house vs. point-of-use.

Free help from Maine CDC

For Contact
What to test for and what results mean (Toxicology) 866-292-3474 toll-free in Maine, or 207-287-4311 · ehu@maine.gov
Well construction, sampling help, treatment types, disinfection (Drinking Water Program) 207-215-7124 · april.bledsoe@maine.gov
Low-income test kit or testing information Maine CDC request form

Maine CDC says private well technical assistance is free.2

  1. Dieter, C.A., and others, 2018, Estimated Use of Water in the United States County-Level Data for 2015 (ver. 2.0), U.S. Geological Survey data release (domestic self-supplied population). https://doi.org/10.5066/F7TB15V5 ↩↩↩

  2. Maine CDC, "Private Well Water." https://www.maine.gov/dhhs/mecdc/healthy-living/health-and-safety/drinking-water-safety/private-well-water ↩↩↩↩↩↩↩

  3. Maine CDC, "Quick Guide to Well Water Treatment" (PDF). https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Well-water-treatment8.27.2026.pdf ↩↩↩

  4. U.S. CDC, "About Maine Tracking Program." https://www.cdc.gov/environmental-health-tracking/php/our-work/about-maine-tracking-program.html ↩

  5. Ayotte, J.D., Medalie, L., and Qi, S.L., 2017, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter based on probability estimates for the conterminous U.S., U.S. Geological Survey data release. https://doi.org/10.5066/F7CN724V ↩↩

  6. MaineTracking Network, "Private Well Water" (data from the Maine Health and Environmental Testing Laboratory). https://data.mainepublichealth.gov/tracking/private-wells ↩↩

  7. Maine CDC Health and Environmental Testing Laboratory, "HETL Water Testing Kits Available" (PDF). https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/Environmental%20Test%20Guide.pdf ↩↩

  8. Maine CDC, "Maine In-State Commercial Drinking Water Labs" (last updated 5/16/2026). https://www.maine.gov/dhhs/mecdc/sites/maine.gov.dhhs.mecdc/files/CommercialListMaineLabs.pdf ↩↩