Arsenic in New Hampshire Well Water

Approximately 30% of tested wells in New Hampshire exceed the EPA arsenic standard. NH was one of the first states to study this problem systematically.

Arsenic is invisible. It is tasteless, odorless, and colorless in water. You cannot see it, smell it, or taste it at any concentration. The only way to know if your well has arsenic is to test.

The Scale of the Problem

~30% of tested NH wells exceed the 10 μg/L EPA limit
38% of NH residents on private wells
10 μg/L EPA maximum contaminant level
1 in 300 estimated cancer risk even at the 10 ppb limit (NRC)

New Hampshire has the same granitic and metamorphic bedrock as Maine — and the same arsenic problem. The difference: NH has been studying it longer and has some of the best private well arsenic data in the country.

Where Does It Come From?

NH's arsenic is naturally occurring — it comes from the bedrock, not from pollution. Two primary geological sources:

1. Granitic Bedrock

New Hampshire is built on granite. The state's granitic and metamorphic bedrock formations contain arsenic-bearing minerals (primarily arsenopyrite and arsenic-substituted pyrite). As groundwater flows through fractures in this bedrock — sometimes for decades — it slowly dissolves arsenic from the rock.

This is why bedrock wells tend to have higher arsenic than shallow wells in glacial deposits. The water has had more contact time with arsenic-bearing rock.

2. Pegmatite Dikes and Specific Formations

Within the broader granitic terrain, certain rock formations are particularly prone to arsenic. Pegmatite dikes — coarse-grained intrusive rocks — can contain concentrated arsenic minerals. The specific bedrock formation your well penetrates matters enormously.

This is why arsenic varies so much from well to well. Two wells a hundred feet apart can penetrate different fractures in different rock, producing completely different arsenic levels.

Geographic Distribution

The NH Geological Survey has mapped arsenic probability by town across the state. The highest-risk areas are concentrated in:

But arsenic can occur anywhere in the state where wells penetrate granitic bedrock. Even areas mapped as "lower probability" can have individual wells with elevated arsenic.

Health Effects

The International Agency for Research on Cancer (IARC) classifies arsenic as a Class I human carcinogen. Long-term exposure to arsenic in drinking water increases the risk of:

The most insidious aspect: cancer can appear up to 40 years after exposure. You cannot wait for symptoms.

Testing for Arsenic

Every private well in New Hampshire should be tested for arsenic at least once. It costs $20-$100 at most labs and could save your life.

See our complete testing guide for labs, costs, and state programs.

Treatment Options

TreatmentTypical CostNotes
Point-of-use reverse osmosis$250-$600 + installationTreats one tap (kitchen sink). Most cost-effective first step. 95%+ arsenic removal.
Whole-house adsorptive media$1,500-$4,000Iron-based media removes arsenic from all water. Media replacement every 1-3 years.
Whole-house reverse osmosis$4,500-$20,000+Treats all water. High maintenance.

NH offers rebates of $5,000-$10,000 for well water treatment systems. If your arsenic exceeds the EPA limit, you likely qualify. Check your eligibility.

Standard carbon filters and water softeners do NOT remove arsenic. A Brita pitcher, a fridge filter, or a basic whole-house carbon filter will not protect you. You need reverse osmosis or arsenic-specific adsorptive media.

Sources

  • NH Geological Survey — Arsenic in New Hampshire Bedrock Wells
  • USGS — Arsenic in Ground Water of the United States
  • EPA — Arsenic Rule (66 FR 6976, January 22, 2001)
  • National Research Council — Arsenic in Drinking Water (2001 Update)
  • IARC — Monographs on Arsenic and Arsenic Compounds
  • NH DES — Private Well Testing Program Data