The flagship Maine well problem
Arsenic treatment for Maine wells
Arsenic is the reason Maine well owners get told to test water that looks, smells, and tastes fine. It leaches from the bedrock the wells are drilled into, it gives no warning at any concentration, and in parts of central and coastal Maine it turns up in a startling share of wells. Statewide, about one in 10 wells exceeds the 10 ug/L federal standard, per a USGS study of Maine bedrock wells.
The good news is that arsenic is one of the most treatable problems on the Maine list, with mature technology at both the tap and the whole-house scale. The order of operations is fixed, though: lab number first, equipment second.
The Maine geography of arsenic
Bedrock arsenic clusters. Research summarized by ScienceDaily found more than 25 percent of sampled wells exceeded the standard in 44 Maine towns, with the heaviest clusters in southern coastal Maine, central Kennebec County, and the Ellsworth area. A Columbia University study of 1,428 wells across 17 Kennebec County towns found 31 percent over the limit. And the extremes are real: in Surry, in Hancock County, 23 percent of 120 tested wells exceeded 100 ug/L, ten times the federal standard, per the Bangor Daily News.
Geography raises or lowers the odds, but it never answers the question. Neighboring wells drilled into different fractures can test wildly differently, which is why the town average is a reason to test, never a substitute for testing. Regional detail lives on the service area pages and the arsenic data page.
The health context, in one sentence
Long-term exposure to arsenic in drinking water is associated with skin changes and an elevated risk of several cancers, including bladder, lung, and skin, per the Maine CDC. That is the whole reason the state asks well owners to test every three to five years, and it is where the health discussion on this page ends: the useful response to arsenic risk is a $32 lab test, not a search spiral. The testing page covers how.
Two ways to treat it: at the tap or at the house
Point of use: reverse osmosis under the sink
A reverse osmosis unit at the kitchen tap treats the water you drink and cook with, which is the exposure that matters most. Maine CDC notes that studies have shown RO up to 95 percent effective at removing the most common form of arsenic found in Maine well water, per its arsenic guidance. Look for units certified to NSF/ANSI standards that list arsenic reduction, described in NSF's standards overview.
Cited cost range: $150 to $1,300 for the unit plus roughly $150 to $300 for installation, per This Old House. Filters and membranes are the recurring line item.
Point of entry: whole-house adsorption media
A whole-house system treats every tap, shower, and appliance. The common design runs the supply through tanks of arsenic-selective adsorption media that are swapped out as they load up. An EPA-hosted New Hampshire DES fact sheet puts typical installed cost at $2,000 to $3,000 plus $200 to $300 per year in media replacement; industry sources cite a broader $1,000 to $5,000 range depending on chemistry and flow, per Rayne Water.
Whole-house makes sense at higher concentrations, in bigger households, or when a buyer or lender wants the entire supply addressed.
Why sizing follows the lab number
No honest installer quotes arsenic treatment without a lab report, because three things on that report drive the design. First, the concentration: a well at 15 ug/L and a well at 150 ug/L need different equipment and different media budgets. Second, the form of the arsenic: the reduced form (arsenite) is harder to capture than the oxidized form (arsenate), and higher-strength systems often add a pre-oxidation step to convert it, a design point covered in the same NH DES fact sheet. Third, the rest of the chemistry: iron, pH, and competing minerals change how fast media exhausts and whether an RO membrane thrives or clogs.
This is why the site's rule is test first, treat second. Bring the report, or start with the testing page, and read your lines with the results explainer. Wells with several problems at once, common in Maine bedrock, belong on the whole-house systems page.
The maintenance reality
Arsenic systems fail silently. Nothing changes at the tap when a membrane wears or a media bed exhausts, so the maintenance schedule is not optional: RO prefilters and membranes on the manufacturer's cadence, media changes budgeted from day one at $200 to $300 per year on a typical whole-house system per the cited fact sheet, and a retest of the treated water about once a year to confirm the reduction is holding.
On cost help: MaineHousing runs a Well Water Abatement program for eligible homeowners with contaminated wells; check its current funding status. The full price landscape across every treatment type is in the Maine treatment cost guide.
Have an arsenic number? Get it quoted.
Tell us your town and the number on the report, and we connect you free with an independent Maine professional who designs and installs arsenic treatment. You get a system sized to your water, quoted from your lab report, by someone local who has seen your geology before.
No report yet? Say so, and the match starts with testing instead. We are a matching service, not a contractor; the details are on the how we make money page.
Questions Maine well owners ask
- How common is arsenic in Maine wells?
- Roughly one in 10 Maine wells exceeds the 10 ug/L federal standard statewide, per USGS. Hotspots run far higher: 29 percent of state-tested wells in Kennebec County, 62 percent in the town of Manchester, and more than 25 percent of sampled wells in 44 Maine towns. Your well's number comes only from a lab test.
- Should I treat one tap or the whole house?
- The main exposure route is drinking and cooking water, which is why under-sink reverse osmosis at the kitchen tap is the common first answer. Whole-house media systems treat every tap and cost more up front plus ongoing media. The lab number, the household, and the budget decide, and a professional sizes from the report.
- Does boiling or a pitcher filter remove arsenic?
- No. Boiling kills organisms but leaves minerals behind, and as water boils off the arsenic that remains becomes slightly more concentrated. Ordinary carbon pitcher filters are generally not certified for arsenic. Look for systems certified to NSF/ANSI standards that specifically list arsenic reduction on the certification.
- What does arsenic treatment cost in Maine?
- Cited national figures: under-sink reverse osmosis units run $150 to $1,300 in equipment plus roughly $150 to $300 to install. Whole-house arsenic systems commonly run $2,000 to $3,000 installed plus $200 to $300 per year in media, with a broader industry range of $1,000 to $5,000 depending on water chemistry and flow.
- How often should treated water be retested?
- Test the treated tap about once a year to confirm the system is still performing, and after any membrane or media change. Arsenic treatment fails quietly, with no change in taste or appearance, so the retest is the only real feedback loop. Keep the untreated number on file too, since media life depends on it.