How to Read a Derry Private-Well Test Result
A laboratory report is a list of analytes, units, reporting limits and measured results. Read those four pieces before shopping for treatment equipment.
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Last checked: August 8, 2026 • Use the laboratory and NHDES for result-specific guidance
Find the Unit Before You Compare the Number
A result only means something beside its unit and reference level. Arsenic may be shown in micrograms per liter, which is numerically equivalent to parts per billion in water, while other items can appear in milligrams per liter. Comparing a measured value in one unit with a standard printed in another is a common way to create a tenfold or thousandfold mistake.
Next, separate 'not detected' from zero. Laboratories report down to a stated detection or reporting limit. A non-detect means the method did not quantify the contaminant above that limit in this sample; it does not establish that no molecule is present. The limit should be low enough to compare meaningfully with the health or aesthetic reference you are using.
Read Each Line in This Order
- Analyte: the specific substance tested, such as arsenic, nitrate, uranium, bacteria, radon or a PFAS compound.
- Result and qualifier: the measured amount plus any flag showing estimated, non-detect or otherwise qualified data.
- Unit: ppb, µg/L, mg/L, pCi/L or another scale appropriate to that analyte.
- Reference: the current New Hampshire standard, action level, advisory or aesthetic guideline that actually applies.
Treatment Must Match the Contaminant
A softener addresses hardness and certain dissolved minerals; it is not a universal contaminant system. Arsenic treatment depends in part on arsenic species and water chemistry. Radon, PFAS, iron, manganese and bacteria each lead to different equipment or corrective steps. Start with the report, then select a system designed for the named problem.
Retesting Is the Proof
Installation is not the finish line. Take the follow-up sample at the point and interval recommended for the treatment system and analyte, keep both reports, and schedule ongoing testing appropriate to a private well. The claim that matters is not 'we installed filtration'; it is that the measured result after treatment moved where it needed to move.
Derry Services Related to This Guide
Have a Derry Lab Report in Front of You?
Call with the analyte, result, unit and reporting limit. Those four items make the first conversation useful.
Derry Well-Test Questions
Does 'ND' mean the water contains none of that contaminant?
It means the laboratory did not quantify it above the method's stated detection or reporting limit in that sample. Check the limit and confirm it is sufficiently below the reference level you care about.
Can I buy one filter for every result on the report?
Usually not. Treatment methods are contaminant-specific and can depend on pH, hardness, competing ions, flow and the measured concentration. Equipment should be selected from the actual water chemistry and verified with a post-treatment test.
Describe the Result or Water Problem
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 — describe the system, result, and timing here.
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.