Guide · Updated October 17, 2026

How do I read well water test results?

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.

Steps

1. Read the header first: sample point, collected and received dates, method, and units. “Kitchen cold, untreated” is not the same as “after softener.” Bacteria has a hold time. mg/L is ppm; µg/L is ppb, a thousand times smaller.
2. Circle total coliform, E. coli, nitrate, and nitrite. If any of those fail, stop. Health department. See coliform bacteria in well water.
3. Convert the rest to mg/L and compare iron, manganese, pH, TDS, sulfate, and hardness to EPA SMCLs or to the extension rule of thumb for hardness.
4. Note what the sheet cannot say: hot-only odor, slime in the toilet tank, a waterlogged pressure tank. Add those in the margin.
5. Only then pick a treatment class from treatment order after the pressure tank or iron filter vs. water softener.

When to test

CDC’s published private-well floor is total coliform, nitrates, total dissolved solids, and pH at a state-certified lab, and again after flooding, well repairs, or a change in taste, smell, or look. EPA’s private-well pages say the same pair (bacteria and nitrate) is the minimum and add tests that follow the house and the geology. Penn State Extension’s testing page is the right tone: certified lab, annual bacteria and nitrate, extra tests for the local geology. If floodwater reached the wellhead, do not start here. Start with Well flooded? What to test and when.

The header is not decoration

• Sample point. If the collector sampled the wrong tap, the report describes the wrong water.
• Date and time, received date. 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.
• Units. 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 to 120 is moderately hard; 120 to 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 to 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.
• Above about 2 to 3 mg/L, or any iron with orange slime in the toilet tank: oxidizer-plus-filtration, and maybe iron-bacteria disinfection. A softener resin bed will become a rust brick.
• Iron high after a filter: 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 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. If lead is on the sheet, do not treat this as an aesthetic project. The dedicated page is blue-green stains and low pH.

Where the bottle came from

A sheet is only as good as the tap and the lab. Start the official search at certified labs by state. A store strip is a screen. Well water test kits explains that split.

Nitrate at or above 10 mg/L as N is the same health-department call in every state that already has a nitrate page: Nitrates in Iowa well water, Nitrates in Minnesota Well Water, Nitrates in Texas Well Water, and Nitrates in Wisconsin Well Water. The inventories include Iowa, Minnesota, Texas, Wisconsin, Michigan, North Carolina, New York, and New Hampshire.

PFAS lines are usually ng/L or ppt, the same unit as EPA’s 4.0 ppt PFOA and PFOS public-system MCLs. That table does not bind a private well.

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. Start at the official state search on certified labs by state, including New York ELAP labs. A mail-in panel such as Tap Score / SimpleLab is a class example of a certified-lab kit, not a ranked pick (Awin tracked URL). Well Diagnosis may earn a commission if you buy through an approved affiliate link on this page. That does not change the price you pay. See the disclosure. Bacteria or nitrate still goes to the health department.

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.