Guide · Updated 2026-08-30

How to read a well water lab report

Circle the lines that change Monday. Bacteria or nitrate still goes to the health department.

A lab report is a table with too many abbreviations and one or two lines that actually change what you do on Monday. Private wells are not public water systems. The numbers on the sheet are still compared, by habit and by usefulness, to EPA’s National Primary Drinking Water Regulations (health-based MCLs) and National Secondary Drinking Water Regulations (aesthetic SMCLs). Those secondary numbers are guidelines for taste, color, odor, and staining. They are not a diagnosis.

CDC says your health department can help you read the sheet. Use that offer when the result is microbiological or nitrate. Use this page when the result is iron, hardness, pH, or a pile of “ND” you do not trust.

The header is not decoration

Before the metals, read:

• Sample point. “Kitchen cold, untreated” is not the same as “after softener.” If the collector sampled the wrong tap, the report describes the wrong water.
• Date and time, received date. Bacteria has a hold time. A sample that sat in a truck is a footnote, not a clean negative.
• Method. EPA 200.7 and 200.8 are common metals methods. Coliform is a different method family. If you paid for iron and the method is missing, ask.
• Units. mg/L is the same as ppm for these dilute waters. µg/L is ppb — a thousand times smaller. Iron reported as 300 µg/L is 0.30 mg/L, which is the iron SMCL. People buy the wrong tank by missing a prefix.

Primary versus secondary

Primary MCLs are health-based limits for public systems. On a private well they are still the numbers health departments talk about.

This site will not interpret those lines as a medical risk score. The next phone call is the health department, not a brand of tank.

Secondary SMCLs are why your laundry looks like it, not why a pediatrician is involved.

USGS Circular 1332 found that aesthetic problems are common in domestic wells: iron, manganese, dissolved solids, pH, and hardness show up in a large fraction of samples. Your sheet looking “a little ugly” is normal geology, not a rare event.

Hardness is often reported as mg/L as CaCO3. There is no federal SMCL for hardness. Rule of thumb used by extension services: below 60 mg/L is soft; 60–120 is moderately hard; 120–180 is hard; above 180 is very hard. Softeners are for hardness. They are not a general “well filter.”

“ND,” “<,” and detection limits

ND (not detected) means the lab did not see the analyte above its reporting limit. It does not mean the molecule cannot exist in the aquifer. If you needed a 0.002 mg/L look at arsenic and the reporting limit is 0.010, you bought the wrong test.

A less-than sign (< 0.05 mg/L) is the same idea. Compare that limit to the SMCL or MCL. Iron < 0.05 is well below 0.3. Iron < 0.5 is useless for deciding whether you are over the stain line.

If hydrogen sulfide is missing from the report entirely, the lab probably did not run it. H2S leaves a bottle. Smell on the cold tap plus a blank line is not a clean bill of health for sulfur.

Iron numbers that change the shopping list

• Below 0.3 mg/L with no stains: you do not have an iron-filter problem. Look at manganese, hardness, or the water heater.
• 0.3–1 mg/L dissolved, clear water that browns in a glass: a catalytic or oxidizing filter, or in some low-iron, low-bacteria cases a softener rated for iron. Read the iron filter vs. softener guide before you let a dealer pick for you.
• Above ~2–3 mg/L, or any iron with orange slime in the toilet tank: you are in oxidizer-plus-filtration territory, and maybe iron-bacteria disinfection. A softener resin bed will become a rust brick.
• Iron high after a filter: either the filter is undersized, the pH is wrong for the media, or bacteria is coating everything.

Ask the lab whether the iron was dissolved, total, or both. Treatment class depends on that.

pH, copper, and “blue-green”

pH 6.2 with blue-green on the sink is a corrosion story. A calcite neutralizer or soda-ash feed is a different class from an iron filter. Installing carbon “for taste” will not add alkalinity. If lead is on the sheet, do not treat this as an aesthetic project.

How to mark up a sheet in five minutes

1. Circle coliform, E. coli, nitrate, nitrite. If any of those fail, stop. Health department.
2. Write the iron, manganese, hardness, pH, TDS, sulfate in a single column with units converted to mg/L.
3. Note hot-only vs. all-tap odor (not on the sheet — add it in the margin).
4. Note slime in the tank (not on the sheet).
5. Only then pick a treatment class from the order after the pressure tank.

Penn State Extension’s testing page is the right tone: certified lab, annual bacteria and nitrate, extra tests for the local geology. EPA’s private-well page has a condition table (flooding, nearby tanks, lead pipes) that tells you what to add.

What the report will not say

It will not say which brand to buy. NSF listings certify claims on a model, not your aquifer. It will not say your pressure tank is waterlogged. It will not distinguish a magnesium anode in the water heater from aquifer H2S — you do that with hot vs. cold taps.

If the report is a sales printout with no lab accreditation number, it is not this document. Get a real one. EPA’s laboratory certification contacts exist so you can find a lab that is allowed to run drinking-water methods in your state.

Bottom line

Read the sample point and the units first. Send primary-standard failures to the health department. Use SMCLs to name the stain and the smell. Then match a treatment class. The sheet is a map. It is not a coupon.