My report says everything is "ND" — is my water safe?

"ND" means not detected above the lab’s reporting limit for the substances tested. It is reassuring for those parameters, but it only covers what was analyzed. Safety also depends on testing the right contaminants for your area.

What’s the difference between a primary and secondary standard?

Primary standards (MCLs) are health-based and enforceable for public systems. Secondary standards are non-enforceable guidelines for aesthetic effects like taste, odor, and staining.

Testing & SafetyHealth-sensitive topic

How to Read Your Well Water Test Results

A lab report can be intimidating. This guide explains units, the difference between health-based and aesthetic standards, and how to prioritize.

By Know Your Well Water Editorial TeamReviewed October 26, 20263 min read

Quick Answer

Read each result against the right reference value and note its nature: a health-based limit (like arsenic or nitrate) is about safety, while a secondary/aesthetic standard (like iron, manganese, or TDS) is about taste, odor, and staining. Watch the units (mg/L vs. µg/L, and nitrate as N vs. NO₃), and remember a partial panel cannot rule out contaminants you didn’t test for.

Step 1 — Check the units

mg/L (ppm) and µg/L (ppb): 1 mg/L = 1,000 µg/L. Arsenic and lead are often in µg/L.
Nitrate: confirm "as N" or "as NO₃" (the EPA 10 mg/L limit is as N).
Hardness: mg/L as CaCO₃ or grains per gallon (1 gpg ≈ 17.1 mg/L).

Step 2 — Identify what kind of standard applies

Type	Examples	What it means
Health-based (MCL)	Arsenic, nitrate	Safety limit — act on exceedances
Action level	Lead, copper	Trigger for action; lead goal is zero
Aesthetic (secondary)	Iron, manganese, TDS, sulfate, chloride	Taste/odor/staining — comfort, not a legal health limit
Classification	Hardness	Descriptive band (soft to very hard)

Public-system limits vs. private wells

EPA MCLs are enforceable for public water systems. Private wells are generally not federally regulated, so these values are reference points for your decisions — not automatic legal limits for your well.

Step 3 — Prioritize your response

1Address any microbiological result first (coliform/E. coli) and any health-based exceedance (e.g., arsenic, nitrate, lead).
2Note aesthetic exceedances for comfort/equipment decisions — these are rarely urgent.
3Consider what was NOT tested; a clean partial panel does not certify overall safety.
4Keep the report as a baseline to compare against future tests.

Don’t over-read a single number

Treatment decisions depend on the full picture — pH, competing ions, and the contaminant form all matter. For health-based results, involve your health department or a certified lab before acting.

Frequently asked questions

My report says everything is "ND" — is my water safe?: "ND" means not detected above the lab’s reporting limit for the substances tested. It is reassuring for those parameters, but it only covers what was analyzed. Safety also depends on testing the right contaminants for your area.
What’s the difference between a primary and secondary standard?: Primary standards (MCLs) are health-based and enforceable for public systems. Secondary standards are non-enforceable guidelines for aesthetic effects like taste, odor, and staining.

Sources & references

National Primary Drinking Water Regulations — US EPA, accessed October 26, 2026
Private Ground Water Wells — CDC, accessed October 26, 2026

This guide is documentary research and general information, not a laboratory analysis or professional assessment of your specific well. See our disclaimer.