How to read a well water report

WellTestList · Friday, September 4, 2026 · reading the PDF

You got the file. Good. Now do not let units, flags, or a salesperson’s paraphrase decide what it means. Read five columns, match units before you compare, and treat EPA limits as the yardstick private wells still use even though the Safe Drinking Water Act does not cover your well.

The short version

Confirm it is your sample. Name, address or well ID, collection date, lab name, and methods should be on the cover. If those are missing, ask for the full report — not a verbal summary.
Read analyte → result → units → reporting limit → MCL / SMCL. Those five tell the story. Method, flags, and QA notes explain confidence. A “High” flag is a cue to look harder, not a substitute for comparing the numbers yourself.
Match units before you compare. 1 mg/L = 1 ppm = 1,000 µg/L = 1,000 ppb. Arsenic is often reported in µg/L while the federal MCL is written in mg/L. PFAS usually sits in ng/L (parts per trillion). Wrong unit, wrong panic — or wrong calm.
Bacteria is Present / Absent, not a concentration. Total coliform Present means a pathway into the well. E. coli Present is the urgent line. Absent / ND is what you want. A strip kit is screening-only and is not this report.

What each column means

The table scrolls sideways on a phone.

Common lab-report columns. Labels vary by lab; the job of each column does not.
Column	What it is	How to use it
Analyte (parameter)	The substance or property tested — nitrate, arsenic, total coliform, pH, hardness.	Make sure you ordered what you think you ordered. A “well panel” is not every contaminant that exists.
Result	What the lab measured in your bottle. Numbers, ND / < RL, or Present / Absent for bacteria.	This is the only column that is your water. Compare it to the limit in matching units.
Units	mg/L (ppm), µg/L (ppb), ng/L (ppt), pCi/L, pH units, Present/Absent.	Convert before you judge. A lead result of 15 µg/L equals 0.015 mg/L — the current federal action level, not “fifteen times over.”
Reporting / detection limit (RL, MRL, LOD)	The smallest amount that method and instrument will report with confidence.	ND means not detected above that limit. It is not proof of zero molecules. It is also not the health standard.
MCL / SMCL / Action Level	The public-system health ceiling (MCL), aesthetic secondary limit (SMCL), or action level (lead, copper).	Private wells are not enforced under these rules, but they are still the honest comparison. Some labs print them; some do not. Keep EPA’s tables open either way.
Method	The approved procedure — e.g. SM 9223 for coliform, EPA 200.8 for metals, 533 / 537.1 for PFAS.	Method matters for PFAS and for lenders. “We tested for forever chemicals” without a method number is not enough. See the PFAS 533 / 537.1 page.
Flag / Qualifier	Lab shorthand: H (over limit), J (estimated), B (blank contamination), U (not detected), and others.	Read the legend on the last page. A flag is a note, not a diagnosis. Ask the lab’s contact if a qualifier is unclear.

Units: the thousand-fold trap

mg/L = ppm — milligrams per liter, parts per million. Nitrate MCLs are written this way.
µg/L = ppb — micrograms per liter, parts per billion. Metals and arsenic often appear here. 1 mg/L = 1,000 µg/L.
ng/L = ppt — nanograms per liter, parts per trillion. Common for PFAS. 1 µg/L = 1,000 ng/L.

Example: arsenic reported at 12 µg/L is 0.012 mg/L. The federal MCL is 0.010 mg/L (10 µg/L). That line is over. If you compared 12 to 0.010 without converting, you would invent a false crisis; if you compared 12 to 10 while thinking both were mg/L, you would invent a false calm.

Nitrate: as nitrogen vs the whole ion

EPA’s MCL for nitrate is 10 mg/L measured as nitrogen (nitrate-N). Nitrite’s MCL is 1 mg/L as nitrogen. Some reports print nitrate as the nitrate ion (NO₃⁻). Those two numbers differ by about a factor of 4.4.

If the label says nitrate-N, N, or “as nitrogen,” compare straight to 10 mg/L.
If it says nitrate (as NO₃) or “nitrate ion,” divide by about 4.4 before comparing to the nitrogen MCL — or ask the lab which convention they used.

High nitrate matters most for infants and pregnant people (blue-baby syndrome risk). Do not wait on a sales visit to sort the units. Call the lab or county environmental health.

Bacteria lines

Total coliform is an indicator group. Present means something got into the well or sample — a cracked seal, a bad sample, surface influence. It is not automatically “fecal,” but it is not a pass.

E. coli Present (or fecal coliform Present, depending on the panel) is the acute line. Stop drinking untreated water from that well. Retest, find the pathway, disinfect with guidance from county or a licensed well contractor. After a flood, follow the sequence on what to test after a flood — disinfection wait, then bacteria on a short hold-time clock.

Absent / Negative / ND is the goal for both. Do not treat a hardware-aisle color strip as the same thing.

Yardsticks you will actually see (EPA, checked Sep 4, 2026)

Private wells are outside federal enforcement. These are still the numbers labs and counties point to. Pulled from EPA’s National Primary Drinking Water Regulations (page updated August 31, 2026) and EPA’s secondary (nuisance) standards guidance.

The table scrolls sideways on a phone.

Common private-well lines. Not every analyte. Confirm your state’s stricter limits where they exist.
Analyte	Federal yardstick	Notes for a homeowner PDF
Total coliform / E. coli	Absent for a private-well sample	Present / Absent, not mg/L. E. coli Present is urgent.
Nitrate (as N)	MCL 10 mg/L	Confirm nitrate-N vs nitrate ion before comparing.
Nitrite (as N)	MCL 1 mg/L	Same nitrogen vs ion caution.
Arsenic	MCL 0.010 mg/L (10 µg/L)	Convert µg/L ↔ mg/L. Local geology drives this.
Lead	Action level 0.015 mg/L (15 µg/L); revised action level 0.010 mg/L begins Nov 1, 2027 for public systems	Often plumbing, not the aquifer. First-draw vs flushed matter — ask how you sampled.
Copper	Action level 1.3 mg/L	Same plumbing story. Taste and blue-green stains are clues, not a diagnosis.
PFOA / PFOS	MCL 4.0 ng/L each (0.0000040 mg/L)	Needs Method 533 and/or 537.1 on scope. See the PFAS methods page.
Iron	SMCL 0.3 mg/L	Staining and taste. Secondary = nuisance, not the same as an MCL.
Manganese	SMCL 0.05 mg/L	Staining / taste. Some states publish tighter health guidance — ask county.
Total dissolved solids (TDS)	SMCL 500 mg/L	Broad mineral load. Useful trend, not a single-toxin answer.
pH	SMCL range about 6.5–8.5	Corrosion and treatment choice. No “MCL” in the primary table.
Chloride / sulfate	SMCL 250 mg/L each	Taste and corrosivity clues.

MCL = Maximum Contaminant Level (health-based, enforceable for public systems). SMCL = Secondary Maximum Contaminant Level (aesthetic / nuisance). Action levels for lead and copper trigger treatment steps at public systems; for a private well they are still the practical compare-to numbers. States can be stricter. We are not inventing a local limit for your county.

What to do when a line is over

Re-read units and nitrate convention. Fix a unit error before you buy anything.
Bacteria Present: Stop drinking untreated water. Call county environmental health. Retest. Find the pathway. Disinfect with real guidance — not a free in-home “test.”
Nitrate / nitrite over: Especially urgent with infants or pregnancy. Use an alternate safe water source until you have a plan from health / extension.
Metals, arsenic, PFAS over: Confirm method and units. Ask whether a resample or a different bottle type is needed. Treatment comes after a named PDF, from someone who does not earn a commission on the softener in the same visit.
Only SMCL over (iron, manganese, hardness, TDS, taste): Nuisance and equipment choice. Still worth fixing. Still not an excuse for a door-to-door pitch that skipped the lab.

What the report will not do for you

It will not invent analytes you did not order. A bacteria-and-nitrate county slip is not a PFAS result.
It will not satisfy a lender by itself if the underwriter named a local lab and a chain-of-custody form. See the home purchase / lender page.
A salesperson’s kitchen-table meter is not this PDF. See the Home Depot free-kit comparison.

What to do with the PDF tonight

Check identity and date on the cover. Save the file somewhere you will find it at sale or refinance.
Walk every flagged line with matching units. Convert arsenic / lead / PFAS before you compare.
Call the lab or county if a qualifier, nitrate label, or method number is unclear. Certified labs have people whose job is to explain results.
If you still need a first PDF, start with county environmental health for bacteria and nitrate, or an independent mail-in kit that emails a report — Tap Score / SimpleLab or National Testing Labs. Read hold-time rules before you fill the bacteria bottle. Cost bands: Tap Score vs NTL vs county.

Not this if…

Someone wants to “interpret” the report only after both spouses are home for a treatment demo. That is a closing tactic. Get the PDF explained by the lab or county first.
You are comparing strip colors to an MCL table. Screening-only. Not this page’s report.
You assumed ND means chemically zero forever. It means below the reporting limit for that method.
You needed Method 533 / 537.1 and the report never names them. Wrong SKU for PFAS. See the methods page.
You collected bacteria Friday and the lab voided it. That is the hold-time clock. Retest Mon–Wed. Details on the flood / hold-time guide.

Sources checked September 4, 2026: EPA National Primary Drinking Water Regulations (updated August 31, 2026); EPA secondary drinking water standards; CDC well-testing guidelines; Rhode Island DOH and Wisconsin Extension well-report reading guides (column layout). Affiliate disclosure: links to Tap Score / SimpleLab may earn WellTestList a commission (rel="sponsored nofollow"). National Testing Labs links are not affiliate links; we earn nothing from them. That does not change who we refuse to list.