Arsenic in New Hampshire Well Water: How to Test, Treat, and Stay Safe

New Hampshire has one of the highest rates of well-water arsenic in the United States. The U.S. Geological Survey and decades of research at Dartmouth's Toxic Metals Superfund Research Program have documented that something on the order of one in five NH bedrock wells contains arsenic above the federal Maximum Contaminant Level of 10 parts per billion (ppb), with hotspots reaching dramatically higher than that. New Hampshire's own drinking-water MCL is stricter at 5 ppb — half the federal limit — which means a well that would pass federal review may still need treatment under NH guidance.

If your home draws water from a private well, arsenic is one of the contaminants you cannot see, smell, or taste, and one of the most important to test for. This guide explains what arsenic is doing in NH groundwater, how to find out whether your well has it, and which treatment approaches actually work.

What arsenic is and how it gets into NH well water

Arsenic is a naturally occurring element in the Earth's crust. In NH, it leaches into groundwater from the same granitic and metamorphic bedrock that produces the state's radon problem — uranium and arsenic are common companions in the geology. The arsenic is dissolved into water that has been in contact with the bedrock for years or decades, which is why bedrock wells (the typical NH private-well design) are far more likely to have elevated arsenic than shallower dug or driven wells.

Arsenic in groundwater exists in two main forms: arsenic-V (arsenate, the oxidized form) and arsenic-III (arsenite, the reduced form). The distinction is important because they behave differently in treatment — arsenic-V is much easier to remove than arsenic-III. Wells in NH typically contain both, in varying ratios. A good water test will tell you the total arsenic and, when needed, the speciation.

Why arsenic matters: the health risks

Long-term exposure to arsenic in drinking water is linked to a meaningful increase in risk for several cancers — particularly skin, bladder, and lung — and to cardiovascular disease, type 2 diabetes, and developmental and cognitive effects in children. The risks are dose-dependent and accumulate over years and decades, which is why even arsenic levels well below older guidance values are now treated as worth removing.

Two facts make this especially relevant in NH:

• There is no "safe" level of arsenic, only a regulatory threshold below which risks are considered acceptable. NH's MCL of 5 ppb reflects newer evidence that risks remain measurable below the federal 10 ppb standard.
• Arsenic is cumulative. Years of drinking 8 ppb water carries more risk than years of drinking 4 ppb water — and most NH residents on private wells do not realize their water has any arsenic at all until they test.

How to test for arsenic in your well

Arsenic testing is simple and inexpensive. The mechanics:

• Use a state-certified lab. NH DES maintains a list of accredited drinking-water labs. Off-the-shelf strip tests can be misleading; lab analysis is the only reliable answer.
• Sample correctly. Most labs supply a kit with a clean bottle and clear instructions (let the cold tap run for several minutes before sampling, fill from a tap closest to the wellhead, etc.). Following the instructions matters.
• Test for the right things. If you are testing your well for the first time, get the standard NH well-water panel, which typically includes arsenic, radon, uranium, manganese, iron, hardness, pH, nitrates, and bacteria. Testing arsenic alone misses the bigger picture, and many of these contaminants share treatment infrastructure.
• Re-test on an interval. NH DES recommends testing well water at least every three to five years, and after any major work on the well or pump. Arsenic levels can drift over time — they do not necessarily stay where they were.

Reading your results

Lab results report arsenic in micrograms per liter (µg/L), which is the same as parts per billion (ppb). The thresholds that matter:

• Below 5 ppb — meets the NH MCL. Most NH water professionals still recommend treatment for any detectable arsenic if you have children, pregnant family members, or long-term plans in the home, but the urgency is lower.
• 5 to 10 ppb — exceeds NH's stricter MCL but meets the federal limit. Treatment is recommended.
• Above 10 ppb — exceeds both NH and federal MCLs. Treatment is strongly recommended; in the meantime, use bottled water for drinking and cooking.
• Above 50 ppb — uncommon but documented in NH hotspots. Treat without delay, and verify the result with a re-test from a second lab if the number is a surprise.

Removing arsenic: your treatment options

Three technologies dominate residential arsenic treatment. The right choice depends on your arsenic level, your water chemistry, your household water use, and whether you want to treat just drinking water or all of the water entering the home.

Reverse osmosis (point of use)

A reverse osmosis (RO) system installs under the kitchen sink and treats only the water you drink and cook with. Water is forced through a semi-permeable membrane that rejects dissolved contaminants — including arsenic-V at very high efficiency — and the treated water is stored in a small tank for use at a dedicated faucet.

RO is the simplest, lowest-cost path to arsenic-safe drinking water. The trade-offs: it does not protect you from showering and bathing in arsenic-containing water (less of a concern at typical NH levels), and it does not address arsenic-III without pretreatment. Look for systems certified to NSF/ANSI 58 specifically for arsenic reduction.

Anion exchange (point of entry / whole house)

Anion exchange uses a tank of resin that swaps arsenic ions for chloride ions, removing arsenic from the entire water supply. It works well at moderate arsenic levels and on water that does not have high competing-ion concentrations (sulfate in particular can compete with arsenic on the resin). The resin is regenerated with brine, similar to how a softener regenerates.

Adsorptive media (point of entry / whole house)

Adsorptive media — typically iron-based products such as granular ferric oxide or titanium-based media — bind arsenic to the media surface as water passes through. There is no regeneration; when the media is saturated, it is replaced. Adsorptive systems handle a wide range of water chemistries and are especially well-suited to NH wells. They tend to be the workhorse choice for whole-house arsenic treatment in this region.

Choosing the right system

Three quick questions sharpen the decision:

1. Do you want to treat all water entering the home, or just drinking water? — POE (whole house) for the former; POU/RO for the latter. Many NH families do both: a POE system to protect the home and a POU RO at the kitchen sink for an extra polish on drinking water.
2. What is your arsenic level, and is the speciation skewed toward As(III)? — At higher levels and with significant As(III), an oxidative pretreatment step is usually needed before adsorptive media or anion exchange will hit target performance.
3. What other contaminants are in the water? — Iron, manganese, hardness, low pH, and competing anions all affect which technology will perform best and what pretreatment is required.

In practice, most NH whole-house arsenic systems are an adsorptive media tank — sometimes preceded by an oxidation/iron-removal stage if the water chemistry calls for it — paired with a kitchen-sink RO for drinking and cooking. ARM has installed hundreds of variations on this design across Southern, Central, and Coastal NH, and the right configuration is always driven by the specific water test.

Maintaining your arsenic system

Treatment systems are durable but not maintenance-free.

• Test treated water annually to confirm the system is still meeting target performance.
• Replace adsorptive media on the schedule the manufacturer specifies for your arsenic level and water use — typically every two to five years.
• For RO, change pre-filters every 6–12 months and the membrane every 2–3 years.
• For anion exchange, regenerate as designed and watch for sulfate breakthrough events on water that has variable sulfate.

Frequently asked questions

Will boiling my water remove arsenic?

No. Boiling does not remove arsenic and can actually concentrate it as water evaporates. Arsenic must be removed by filtration or treatment, not by heat.

Will a standard pitcher filter or refrigerator filter remove arsenic?

Most do not. Some carbon-block filters are certified to NSF/ANSI 53 for arsenic reduction, but verify the specific certification on the box. Default to RO or POE if arsenic is your main concern.

Is showering in arsenic-containing water dangerous?

Skin absorption of arsenic from typical NH well-water concentrations is minimal compared to ingestion. Drinking water is the dominant exposure route, which is why RO at the kitchen sink delivers most of the health benefit even without whole-house treatment. That said, whole-house treatment is the most thorough approach for households planning to stay long-term.

How much does an arsenic treatment system cost in NH?

A point-of-use RO system typically runs $400–$1,200 installed. A whole-house adsorptive media system typically runs $2,500–$5,000 installed depending on capacity, water chemistry, and whether oxidative pretreatment is required. Always get a quote based on your actual water test.

Can I install a system myself?

RO systems are within reach for handy homeowners. Whole-house arsenic treatment is not — sizing, pretreatment, plumbing, and post-test verification matter, and the consequences of a wrong choice are health-relevant. Use a water-treatment professional with arsenic-specific experience.

Get your NH well tested and treated

If your well has never been tested for arsenic — or if your last test was more than five years ago — start there. If you have a result above 5 ppb, treatment should be on the near-term plan. ARM provides comprehensive water testing, system design, and installation across Southern, Central, and Coastal New Hampshire.

Call 603-644-1207 to schedule a water assessment, or request a quote at radonh2o.com/contact.