Ask a Merrimack seller when their well was last tested and you'll get one of two answers: a specific date, or a shrug. New Hampshire treats both answers the same way under the law. Neither one is a violation. But only one of them tells you anything useful before you close.
That gap between "legal" and "informative" is the thing most buyers miss about water quality in a town like Merrimack, where the water source itself splits along an old boundary line: town water and sewer along the Route 3 corridor, private wells everywhere the pipes never reached. New Hampshire doesn't require a well test before a sale. It requires disclosure of the well's history. Those are not the same obligation, and the distance between them is exactly where a buyer either gains real leverage or loses it by waiting too long to ask.
What the Law Actually Requires (And What It Doesn't)
New Hampshire has two statutes that touch a private well at closing, and they ask for very different things. RSA 477:4-d requires a seller of a one-to-four-family home to give the buyer written information about the private water supply, including its type, its location, and the date of the most recent water test, along with any known problems. RSA 477:4-a separately requires a notification that radon and arsenic can occur in New Hampshire groundwater and that testing is recommended.
Read those together and the picture is clear: New Hampshire doesn't tell a seller to test the water. It tells a seller to report whatever they already know, including how old that knowledge is. A seller who tested in 2020 and never again can disclose "last tested 2020, no known problems" and be fully compliant. That sentence sounds reassuring. It is also six years old on a well that sits in fractured granite bedrock where conditions can shift.
Lenders close part of that gap on their own terms. FHA and VA loans, and many conventional loans on well-served properties, require a passing water test as a condition of financing, regardless of what state law demands. So the real requirement most Merrimack buyers face isn't statutory. It's contractual, buried in the loan file, and it means the test is happening one way or another. The only open question is whether it happens early enough to be useful.
Route 3 Splits Merrimack Into Two Different Water Questions
Merrimack doesn't have one water story. It has two, and which one applies to a given address depends almost entirely on proximity to the Route 3 corridor. Properties closer to that stretch, including much of the commercial and residential mix along the Daniel Webster Highway corridor, typically sit on town water and sewer. Move away from that spine, into areas like Thorntons Ferry Road or the properties ringing Baboosic Lake, and private wells become the norm rather than the exception.
That distinction matters because it means "Merrimack home" tells you almost nothing about which disclosure obligations and which lender conditions apply. Two houses ten minutes apart can have completely different water situations, and a buyer comparing listings by price and square footage alone will miss it every time. The only way to know is to ask directly, early, and in writing.
What a Standard Panel Actually Covers, and What It Costs
The New Hampshire Department of Environmental Services recommends a Standard Analysis for anyone buying a home on a private well, not a single test but a panel. Here's what that panel typically includes and why each piece matters for a Merrimack property specifically.
| What's tested | Why it matters here | Typical cost or fix |
|---|---|---|
| Arsenic | Naturally occurring in fractured granite bedrock across southern New Hampshire; roughly one in three private wells shows detectable levels, and the state lowered its health standard to 5 parts per billion in 2021 | Panel cost is part of the $85 to $130 standard analysis; point-of-use treatment systems run $1,500 to $3,000 installed |
| Radon | NHDES estimates most private wells in the state exceed the suggested action level, and Merrimack's housing stock has a lot of finished basement living space where the gas can accumulate | Testing runs $50 to $100; an aeration or carbon system to bring levels down runs roughly $800 to $2,000 |
| PFAS | Added to New Hampshire's mandatory seller disclosure list in 2025, alongside radon, lead, and arsenic; Merrimack has a documented history of regional groundwater investigation tied to a former manufacturing site in town | Testing is typically bundled into a comprehensive panel running $400 to $700; a rebate program exists for qualifying private well owners |
| Bacteria and nitrate | Basic indicators of surface contamination or septic influence, required by most lenders regardless of well location | Often $25 to $75 as a standalone test |
| Flow rate | Confirms the well can actually supply the household, separate from water quality entirely | A dedicated flow test is a separate line item from water quality testing |
Against a New Hampshire single-family median sale price sitting near $575,000 as of mid-2026, a $100 to $130 standard panel is not a meaningful expense. It's the cheapest form of leverage a buyer can create in the entire transaction, because whatever it finds becomes negotiable while the inspection contingency is still open.
The PFAS Line Deserves a Straight Answer, Not a Scare
The reason PFAS sits on New Hampshire's disclosure list at all traces back to a manufacturing facility that operated in Merrimack for decades. Groundwater investigation around that site expanded outward into surrounding towns over several years, and the company involved has since demolished the facility and continued to fund water line extensions and treatment systems for affected properties under a court-approved agreement. That obligation is still active: the Concord Monitor reported in March 2026 that the company agreed to pay roughly $1.71 million toward a water main project in Londonderry, one of the other towns covered by the same 2018 consent decree. That history is a matter of public record through the state's own tracking, not a reason to treat every Merrimack well as suspect.
What it does mean practically is that a buyer on a private well in Merrimack has a specific, answerable reason to ask whether PFAS was included in any past testing and to include it in a pre-closing panel if it wasn't. The state's PFAS Removal Rebate Program exists specifically because this is a known, mapped, addressable issue in this part of New Hampshire, not an open question mark. A seller who can point to a clean, recent result on this specific line closes faster and with less back-and-forth. One who can't should expect the buyer to ask, because the disclosure law now requires the topic to be on the table either way.
The Window Where Leverage Still Exists
Testing during the inspection period, not after, is what turns a result into a negotiating tool instead of a surprise. A result above the state arsenic standard or an elevated radon reading is not, on its own, a reason to walk away. Arsenic and uranium respond to point-of-entry treatment. Radon strips out with an aeration unit. Bacteria issues often resolve with shocking the well and retesting. Every one of these has a known cost range, and a known cost range is something both sides can negotiate around, whether that means a credit, a price adjustment, or the seller installing treatment before the closing date.
The buyers who lose that leverage are the ones who skip the test, rely on an old disclosure, and find out about a problem after they own the well outright. At that point the cost of fixing it is theirs alone, with no seller left to negotiate with.
A Few Direct Questions
Does the seller have to pay for well testing in Merrimack? No. New Hampshire law doesn't assign the cost to either party. In practice, the buyer most often orders and pays for testing as part of due diligence, though this is negotiable between the parties.
What if the well tests fine but the seller's disclosure is out of date? A clean current test supersedes an old disclosure in practical terms, since it's the information a lender and a buyer will actually rely on. Ask for a current test regardless of what the disclosure states.
Is PFAS testing automatically included in a standard panel? Not always. NHDES recommends a Standard Analysis that covers arsenic, bacteria, lead, uranium, and related minerals, but PFAS is often a separate add-on. Given Merrimack's history, ask specifically that it be included.
A well test costs less than a single month of a mortgage payment and it tells you more about a Merrimack property than the listing photos ever will. If you're comparing homes on and off the Route 3 water line and want a straight read on what a specific address requires before you write an offer, reach out to Connie Distasio. Let's Connect.
