Private wells
Maine well water: who's on a well and what to test for
People on private wells
629,800
Homes on wells
48.5%
Est. above arsenic limit
102,500
Every Maine county
Sorted by people on private wells. Arsenic and nitrate are modeled for typical wells in the county, not measured at yours; depth is the median of domestic well records.
| York County | 94,800 | 42% | n/a | n/a | 245 ft |
| Cumberland County | 88,600 | 31% | n/a | n/a | 240 ft |
| Penobscot County | 64,100 | 43% | n/a | n/a | 200 ft |
| Kennebec County | 61,500 | 50% | n/a | n/a | 225 ft |
| Androscoggin County | 42,400 | 38% | n/a | n/a | 262 ft |
| Aroostook County | 40,200 | 61% | n/a | n/a | 150 ft |
| Hancock County | 38,000 | 71% | n/a | n/a | 220 ft |
| Oxford County | 35,200 | 63% | n/a | n/a | 300 ft |
| Somerset County | 28,300 | 59% | n/a | n/a | 225 ft |
| Waldo County | 25,600 | 65% | n/a | n/a | 200 ft |
| Lincoln County | 25,500 | 73% | n/a | n/a | 215 ft |
| Washington County | 20,800 | 68% | n/a | n/a | 200 ft |
| Knox County | 20,200 | 52% | n/a | n/a | 191 ft |
| Sagadahoc County | 18,000 | 51% | n/a | n/a | 210 ft |
| Franklin County | 17,000 | 62% | n/a | n/a | 240 ft |
| Piscataquis County | 9,700 | 63% | n/a | n/a | 200 ft |
Shading: red is among the highest counties nationally, amber the middle, green the lower range. Click a column to sort.
Test first, then treat what the test finds
We may earn a commission from links below, at no cost to you. Picks follow the testing order, not who pays. How we make money.
1. Certified lab well test
Start here, every year
A mail-in kit analyzed by a certified lab measures bacteria, nitrate, arsenic, metals and more. Test strips cannot measure arsenic or uranium reliably.
2. Sediment pre-filter
Sand, silt or cloudy water
A 5-micron cartridge after the pressure tank catches sand, silt and rust before they reach fixtures or other filters. Cartridges are cheap and swap every few months.
3. Iron and sulfur filter
Orange stains or rotten-egg smell
Air-injection or oxidizing-media filters remove orange staining and rotten-egg smell. Size one from a lab result for iron, manganese and hydrogen sulfide.
4. UV disinfection system
Coliform bacteria in a test
Inactivates bacteria and viruses; usually for private wells or after boil notices.
5. Under-sink reverse osmosis
Arsenic, nitrate or uranium in a test
The most thorough option for drinking water: PFAS, lead, nitrate, arsenic and more. Look for NSF/ANSI 58.
6. Whole-house well filter
Several problems at once
Multi-stage sediment and carbon for every tap. Add UV if bacteria shows up, and choose stages from your lab results, not a guess.
Questions
Which Maine counties rely most on wells?+
By share of homes: Lincoln County (73%), Hancock County (71%), Washington County (68%), Waldo County (65%), Oxford County (63%). By number of people: York County (94,800), Cumberland County (88,600), Penobscot County (64,100).
Is arsenic a problem in Maine wells?+
USGS estimates about 102,500 Maine well users have water above the 10 microgram per liter arsenic limit that applies to public systems. Arsenic has no taste or smell, so only a lab test finds it.
Do I have to test my well when I sell a house in Maine?+
We could not confirm a statewide rule for Maine. Check with your county health department. Buyers can still make a lab test a condition of the offer.
How often should I test my well?+
No federal law covers private wells. EPA's drinking water limits apply to public water systems, so testing and treating a private well is up to the owner. EPA and CDC recommend testing at least once a year for coliform bacteria, nitrate, pH and total dissolved solids, and testing for arsenic, uranium, radon and other local concerns based on where you live.
Well-user counts, arsenic and nitrate figures are each a modeled estimate built from national datasets, not a count of tested wells, and well depths summarize drilling records rather than every well. Your own well can be very different from the county average, which is why the only answer for your home is a lab test. Sources: EPA Office of Research and Development, Water Source 2020 (private well estimates by census block); CDC Environmental Public Health Tracking, Well Water Index (from USGS nitrate and arsenic models); USGS, county-level domestic well population with arsenic above 10 micrograms per liter (Ayotte and others, 2017); USGS Synthesized Domestic Well Database for the Conterminous United States (SynDWell-US), McCarthy and others, 2025 (depth, where a county has 30+ usable records).