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Arsenic in Well Water Treatment in New Hampshire
Arsenic is naturally present in New Hampshire bedrock and is odorless and tasteless. A licensed local contractor can test your well and recommend the right system. Start with a free in-home water test and quote.
Your request goes to an independent local water treatment contractor serving New Hampshire, not a national lead list.
What it is and why New Hampshire wells need it
Arsenic is the contaminant that brings most New Hampshire well owners to a water test, and for good reason. It dissolves naturally out of the granite and metamorphic bedrock that underlies much of the state, and it is completely invisible, with no color, taste, or smell. The only way to know your level is to test.
A United States Geological Survey study of private bedrock wells in southeastern New Hampshire found that nearly one in five exceeded the federal arsenic limit of 10 micrograms per liter, with higher rates in parts of Hillsborough and Strafford counties. In 2021, New Hampshire set its own enforceable standard at 5 parts per billion, half the federal limit and one of the strictest in the country.
Arsenic exposure is a long-term health issue, not an emergency. NHDES and the EPA link long-term exposure to a higher risk of several cancers and other effects, which is why the state tightened its standard. The reassuring part is that arsenic is very treatable once a test shows how much is present and which form it takes.
How a contractor treats arsenic
Adsorptive media filters
Iron-based or titanium-based media bind arsenic as water passes through. A contractor can size these for the whole house or for a single tap. The media has a finite capacity and is replaced every one to three years, and its performance drops when Arsenic-III is present or pH is above 7.5.
Anion exchange
An anion exchange system trades arsenic for harmless ions on a resin bed. It removes Arsenic-V well across a range of pH and regenerates with ordinary salt, so operating costs are low. It is often paired with a calcite neutralizer for pH.
Reverse osmosis at the tap
A point-of-use reverse osmosis system under the kitchen sink pushes water through a fine membrane and removes about 95 percent of Arsenic-V. Because it treats only one tap, it is a lower-cost option for drinking and cooking water.
Why the arsenic species matters
Arsenic shows up as Arsenic-III or Arsenic-V. Arsenic-III carries no electrical charge, so anion exchange and membranes remove it less effectively. A contractor may add a simple pre-oxidation step, using chlorine or a manganese dioxide media, to convert Arsenic-III to the more easily removed Arsenic-V before the main treatment.
What to expect
- 1
Request a free in-home water test
Use the form or call. A licensed local contractor sets up a visit at no cost.
- 2
The contractor tests your water and reviews the results
You get a plain explanation of what is in your water and what it means.
- 3
You get a written, itemized recommendation and quote
If treatment makes sense, the recommendation is matched to your water, with the cost in writing.
- 4
The contractor installs the system
If you choose to proceed, the contractor installs and configures the system for your home.
- 5
The contractor confirms performance and explains maintenance
You leave with a clear maintenance schedule and, where relevant, a retest plan.
For arsenic, NHDES recommends retesting the treated water quarterly for the first year and twice a year after that, so you can confirm the system is doing its job.
How much arsenic removal costs
It depends on your water, but New Hampshire has solid benchmarks. As 2026 New Hampshire market context, an NHDES survey found a median installed cost of about $1,200 for a point-of-use system, with median annual maintenance around $343, and about $3,000 for a whole-house system, with median annual maintenance around $550. A point-of-use reverse osmosis unit for arsenic commonly runs $1,200 to $2,000 installed, and a whole-house single-filtration system generally falls between $1,500 and $3,000.
Your exact number depends on your arsenic level and species, your water chemistry and pH, and whether you treat one tap or the whole home. That is what the free in-home test and written, itemized quote pin down, so you are working from a price for your well rather than a general range.
Where arsenic runs highest in New Hampshire
Arsenic follows the bedrock, not the town line, so two homes on the same road can test very differently. Two parts of New Hampshire concentrate the demand for arsenic treatment: the Lakes Region, where homes draw from granite and metamorphic bedrock, and the southeastern arsenic belt across Strafford and Hillsborough counties. A USGS study of private bedrock wells in southeastern New Hampshire found that nearly one in five exceeded the federal limit of 10 micrograms per liter, with higher rates in parts of Hillsborough and Strafford counties.
How much the rock matters shows up in the state's own data. NHDES reports that arsenic exceedance varies sharply from one bedrock unit to the next: statewide, about 25 percent of wells in the Concord Granite and about 28 percent in the Spaulding Tonalite exceed the federal limit, well above the one-in-five average. A neighbor's clean test says nothing about your own well, which is why testing is the only way to know your level.
For a Lakes Region owner around Laconia or a Strafford County owner near Dover or Barrington, the takeaway is the same. Elevated arsenic is common enough in these areas that a test is the sensible first step, and a licensed local contractor can size a system to whatever your result shows.
Arsenic-III versus Arsenic-V and why it changes the system
Arsenic shows up in well water as one of two species, Arsenic-III (arsenite) or Arsenic-V (arsenate), and the difference is not academic. It changes which system works and whether an extra step is needed.
Arsenic-V carries a negative charge in water, so it is removed efficiently by anion exchange and by reverse osmosis membranes. Arsenic-III carries essentially no charge, so those same methods remove it far less effectively. NHDES notes that reverse osmosis removes roughly 95 percent of Arsenic-V but only about 60 percent of Arsenic-III.
The fix is a pre-oxidation step. A contractor can convert Arsenic-III to the more easily removed Arsenic-V using chlorine or a manganese dioxide media before the main treatment, which is why the arsenic species is one of the first things a good contractor checks when sizing a system.
Where this fits
Related services a contractor often pairs with this one:
Serving well owners in these and other New Hampshire towns:
Read: New Hampshire Arsenic in Well Water: A Homeowner's GuideNot sure what is in your water? Start with a test.
A free in-home water test shows exactly what your well needs. For a home with several contaminants, compare whole-house water treatment.
Frequently Asked Questions
How much does it cost to remove arsenic from well water?
Cost depends on the arsenic type and level and whether you treat the whole house or only drinking water. As 2026 New Hampshire context, an NHDES survey found a median installed cost of about $1,200 for a point-of-use system and about $3,000 for a whole-house system. A free in-home test gives you an exact quote.
What is the best way to remove arsenic from well water?
The right method depends on the arsenic species and concentration. Common approaches are adsorptive media, anion exchange, and reverse osmosis. A licensed contractor tests your water and sizes the system.
What is a safe level of arsenic in drinking water?
New Hampshire's maximum contaminant level is 5 parts per billion, set in 2021 and half the federal limit, and the federal EPA maximum contaminant level is 10 parts per billion. Because arsenic is a long-term exposure issue, lower is better, and a test is the only way to know your level.
Do I need a whole-house arsenic system or a point-of-use filter?
A point-of-use system treats water at a single tap, usually the kitchen, for drinking and cooking. A whole-house system treats all water entering the home. Which one fits depends on your test results and how you use your water, and the matched contractor advises based on the test.
What is the difference between Arsenic-III and Arsenic-V?
Arsenic-III (arsenite) and Arsenic-V (arsenate) respond differently to treatment. Arsenic-V carries a charge and is removed well by anion exchange and reverse osmosis, while Arsenic-III carries little charge and is harder to remove, so a contractor often adds an oxidation step to convert it to Arsenic-V first.
Is arsenic worse in the Lakes Region or in Strafford County?
Both areas see elevated arsenic because both sit on New Hampshire's granite and metamorphic bedrock, which is the source. Southeastern New Hampshire, including Strafford County, is a documented arsenic belt where a USGS study found higher-than-average rates, and NHDES data show exceedance varies most by the specific bedrock unit a well draws from, about 25 percent in the Concord Granite and 28 percent in the Spaulding Tonalite. Arsenic is common enough in both regions that only a test tells you your own level.
Start with a free in-home water test
A licensed local contractor will test your water, explain the results, and give you a written quote. No obligation.
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