Can I taste or smell arsenic in well water?

No. At the concentrations found in Maine wells, arsenic has no taste, smell, or color, and it does not stain fixtures or laundry. Water with an exceedance can look and taste excellent. A certified lab test is the only detection method, which is why Maine CDC puts arsenic on a routine testing cadence rather than a wait-for-symptoms one.

My neighbor tested low. Does that clear my well?

No. Bedrock wells draw from individual fracture networks, and USGS sampling in Maine has found sharply different arsenic levels in wells a short distance apart. A neighbor’s result is weak evidence either way. The town-level data on this page tells you how common exceedances are nearby; only your own sample tells you your number.

Do I treat at the tap or treat the whole house?

The main exposure route for arsenic is drinking and cooking water, so a point-of-use reverse osmosis unit at the kitchen tap is the common first option. Whole-house adsorption systems treat every fixture and suit households that want full coverage or have higher confirmed levels. A professional weighs your number, your plumbing, and your budget.

How often should I retest once treatment is installed?

Follow the schedule the installer and equipment maker set, and include a lab verification test after installation to confirm the treated water meets the guideline. Media beds and membranes exhaust gradually, so periodic treated-water tests are the honest proof the system still performs. Keep every result with your well records.

Arsenic in Maine wells: the data, town by town

One Maine well in 10 exceeds the federal arsenic standard of 10 ug/L, according to a USGS survey of bedrock wells statewide. That is the baseline, and it understates the places that matter: in parts of central Maine, tested exceedance rates run three to six times higher. This page collects the published numbers in one table, explains the geology in plain language, and lays out what to do at each result level. It is written to be accurate rather than alarming, because the arsenic story in Maine is genuinely serious and genuinely manageable in the same breath.

The published numbers

Arsenic exceedance findings, Maine wells

Exceedance means above the 10 ug/L federal standard unless noted. Each row links its source.

Area	Finding	Source
Maine statewide	About 10 percent of bedrock wells exceed	USGS
44 Maine towns	More than 25 percent of sampled wells exceed	USGS analysis
Kennebec County	29 percent of state-tested wells exceeded, 2005 to 2009	Press Herald
17 Kennebec towns	31 percent of 1,428 wells exceeded, 2006 to 2011	Columbia study
Manchester	62 percent of tested wells exceeded	Press Herald
Surry (Hancock County)	23 percent of 120 wells exceeded 100 ug/L, ten times the standard	Bangor Daily News

The USGS work identifies three clusters where exceedances concentrate: southern coastal Maine, central Kennebec County, and the Ellsworth area, per the same analysis that flagged the 44 towns. Those clusters map onto this site's regional pages for the Augusta and Kennebec Valley area, the Ellsworth and Downeast area, and the southern coast around Portland. Living outside a cluster lowers the odds; it does not zero them, which is why the statewide one-in-10 figure stays the floor for every untested well.

Why the bedrock does this

Maine's drilled wells pull water from cracks in hard rock, not from sandy aquifers. Much of central and coastal Maine sits on metamorphosed marine sediments laced with sulfide minerals, and those minerals carry arsenic. Groundwater creeps along the fracture network for years, reacting with mineral surfaces, and where the chemistry runs the wrong way, arsenic dissolves into the water that a well later pumps up.

Fracture flow explains the pattern that surprises homeowners most: extreme local variation. Two wells a few hundred feet apart can intersect different fractures with different water, so one tests clean while the other exceeds several times over. It also explains why town-level statistics, like the table above, are guidance about odds rather than verdicts about any single well. The rock decides well by well, and only a sample settles it.

Long-term exposure to arsenic in drinking water is associated with increased risk of several cancers and other health effects, per Maine CDC's private well program. That is the health picture in one sentence, and the response it points to is not worry: it is a test.

Testing: the cadence and the trigger moments

Maine CDC recommends testing for arsenic every three to five years, alongside uranium, radon, and fluoride. Test outside the cadence when the situation changes: a new well, work on the well or pump, a home purchase (covered in the home-buying guide), or a prior result near the guideline. The state lab and four certified private labs run the analysis; kits, addresses, and ordering steps are on the testing recommendations page.

What to do at each result level

Under 10 ug/L. Below the federal standard and Maine's guideline. No action beyond staying on the three-to-five-year cadence, and consider retesting sooner if the result sat close to 10, since bedrock well chemistry can drift over time.

10 to 50 ug/L. A confirmed exceedance is a treatment decision, not an emergency evacuation of the kitchen. First confirm: retest before spending, because a single sample can mislead and treatment gets sized to a number you trust. Once confirmed, the usual choice is between a point-of-use reverse osmosis unit for drinking and cooking water and a whole-house adsorption system, both covered on the arsenic treatment page. Many households in this band drink bottled water during the weeks between confirmation and installation, a judgment call rather than a rule.

Over 50 ug/L. Move promptly. Retest to confirm, switch to an alternative source for drinking and cooking while you sort treatment, and have a professional evaluate both point-of-use and point-of-entry options together, since higher concentrations change system design. Results at this level also make the case for testing again after installation to verify performance, walked through in the results explainer.

Reading the statistics honestly

One caveat keeps this page accurate rather than dramatic: the different figures come from different kinds of sampling. The USGS statewide and 44-town findings rest on structured scientific sampling designed to represent the underlying geology. The Kennebec and Manchester figures describe wells whose owners chose to send in a sample, and self-selected testing can run in either direction: worried owners in known hotspots test more, which can raise measured rates, while the figures still miss every never-tested well nearby. That is why this page reports both kinds side by side and labels the years and sample counts. The honest summary is not that 62 percent of Maine wells are contaminated; it is that exceedance odds vary enormously by town, they are high enough everywhere that testing is rational, and in the mapped clusters they are high enough that not testing is the risky choice.

The live data sources

Two state resources keep this picture current, and both outrank any secondhand summary, this page included. The Maine Tracking Network publishes private well testing and exceedance data by geography, drawn from state lab results. The Maine Geological Survey covers the groundwater and bedrock context behind the numbers. Journalists and researchers citing Maine arsenic figures should pull from those two and the USGS publications linked above.

Have a number and want it handled?

If your report shows arsenic, we connect you free with an independent local professional who treats it for a living, sized to your result and your house. If you have no report yet, say so in the form and the match starts with a test instead.