Private Well Water Testing in Derry, New Hampshire

The Local Rule Most People Meet Too Late

The Town of Derry requires testing of private wells in connection with either a certificate of occupancy or a property transfer, and publishes private well testing resources for residents. If you are selling, buying or completing a build, that testing is part of the process rather than something optional you might get round to. The expensive version of this is discovering it with a closing date already set; the cheap version is testing early, when a result you do not like still leaves time to do something about it. (Town of Derry, read August 2026.)

Behind the testing itself is a laboratory, not this site and not a contractor. What a local contractor is useful for is what happens after a result — whether a number can be treated, with what, and at what cost. Interpretation of a health-based result belongs with NHDES guidance and, where it matters, a medical professional.

What Is Worth Testing For in This Bedrock

• Arsenic — the headline one here. NHDES estimates it exceeds New Hampshire's 5.0 ppb standard in roughly 25 to 30 percent of private wells, and the state standard is half the federal limit of 10 ppb.
• Radon in water — common in New Hampshire's granite, and a separate question from radon in air.
• PFAS — detections have been rising across the state, and NHDES maintains dedicated guidance for private wells.
• Bacteria — total coliform and E. coli, the standard transaction test and the one most likely to be affected by a compromised well cap.
• The routine chemistry — iron, manganese, hardness, pH, nitrate, sodium, chloride, uranium. Several of these are nuisance issues rather than health ones, and it is worth knowing which is which.

Reading the Result Without Panicking

A test result is a set of numbers against a set of standards, and the useful first move is separating the health-based limits from the aesthetic ones. Iron and manganese stain laundry and taste unpleasant; they are not the same category of problem as arsenic above 5.0 ppb. Confirm which standard each number is being measured against, and where a health-based figure is exceeded, note the actual value rather than just that it failed — the level determines what treatment is appropriate and how much it costs. NHDES publishes guidance on interpreting private well results, and it is written for homeowners rather than for chemists.

What Happens After a Result You Do Not Like

• Confirm it — a single result on a single day is a data point. Where a health-based limit is exceeded, retesting confirms it is real before money is spent on it.
• Match the treatment to the contaminant — there is no general-purpose fix. Arsenic, radon, PFAS, iron and hardness are treated by different means, and a system that addresses one may do nothing for another.
• Establish the target — treatment reduces a named contaminant to a measured level. Ask what level the proposed system is expected to achieve, and how that will be verified.
• Retest after installation — this is the step people skip, and it is the only thing that demonstrates the system did what was claimed for it.

Ask About Testing

No water this morning, a pump short-cycling, a pressure tank past its life, or a test result you do not know how to read — put it here and one licensed local contractor calls back.

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What Usually Turns Up Alongside It

Well work rarely stays in one lane. The pump raises the tank, the tank raises the pressure switch, and a transfer test raises everything that is dissolved in the water.