New Hampshire Arsenic in Well Water: A Homeowner's Guide

Arsenic is a naturally occurring element found in rock, soil, and groundwater. In New Hampshire it dissolves out of the granite and metamorphic bedrock that underlies much of the state, which is why it turns up in private wells with no nearby industrial source. It has no color, taste, or smell, so no one can detect it without a laboratory test.

Because it comes from the bedrock, arsenic is mostly a concern for drilled bedrock wells rather than shallow dug wells, though either can be affected. Two homes on the same road can have very different levels, since arsenic follows the rock rather than the property line.

Arsenic is widespread enough that testing is the only responsible assumption. A USGS 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, and the rate reached about 21 percent in Hillsborough and Strafford counties.

Statewide, USGS probability mapping ties arsenic to specific bedrock units, and median arsenic in private bedrock wells is similar across counties. In other words, there is no New Hampshire town where you can safely assume your well is clear without testing it.

This is a long-term exposure issue, not an acute poisoning risk at the levels found in most wells. The concern is years of drinking water with elevated arsenic, not a single glass.

The EPA links long-term exposure to inorganic arsenic in drinking water to a higher risk of several cancers, including skin, bladder, and lung cancer, and to non-cancer effects on the cardiovascular, skin, and other systems. New Hampshire weighed this evidence when it tightened its own standard. None of this is cause for panic, and it is exactly why the state and federal agencies recommend knowing your level and treating water that exceeds the standard.

In 2021, New Hampshire lowered its enforceable standard for arsenic to 5 parts per billion, half the federal limit of 10 parts per billion, becoming one of the first states in the country to do so (NHDES). The standard applies to public water systems, but it is also the sensible benchmark for a private well: if your level is above 5 parts per billion, treatment is worth serious consideration.

You cannot see, taste, or smell arsenic, so a laboratory test is the only way to know your level. You can send a sample to a New Hampshire accredited laboratory, or have a licensed local contractor collect a sample during a free in-home visit. NHDES recommends including arsenic in a standard water analysis every three to five years.

If your home is on a bedrock well and has never been tested, that is the place to start. A test also tells you which form of arsenic is present, which matters for choosing a treatment system.

Arsenic is very treatable. According to NHDES, the common approaches are adsorptive media filters that bind arsenic, anion exchange systems that trade it off a resin bed, and reverse osmosis systems at the kitchen tap. A licensed contractor sizes the system to your water, your level, and whether you want to treat the whole house or just drinking water.

One detail matters enough to have its own guide: arsenic comes in two forms, and the form changes which system works best and whether a pre-treatment step is needed. If you want to understand that before talking to a contractor, the companion guide on arsenic species walks through it.

Once you have a number, it is easy to interpret. Below 5 parts per billion, your well meets New Hampshire's standard. Between 5 and 10 parts per billion, you are above the state standard but below the older federal limit, and treatment is worth considering. Above 10 parts per billion, you exceed both standards, and treatment is the clear path.

A single result is a snapshot. Arsenic levels can shift with the seasons and with how much the well is used, which is why a standard analysis every three to five years is the baseline recommendation, and why treated water is retested on a schedule rather than tested once and forgotten.

Because arsenic is a concern only when swallowed and is not absorbed through the skin, NHDES notes that a point-of-use system at the kitchen tap is often the most cost-effective solution for arsenic alone. A whole-house system makes sense when arsenic levels are high, when iron also needs to be removed, or when you simply want every tap covered.

A licensed local contractor weighs your level, your water chemistry, and how your household uses water before recommending one approach or the other. The free in-home test is what makes that recommendation specific to your home rather than generic, and it is the reason there is no single right answer that fits every well.