How to read a well-water lab report
A filter quote is a guess until you can point at a line on a lab report. This page explains the lines that matter for staining and odor, and the lines that mean you should stop shopping.
Updated
Filter sellers will talk as soon as you describe a stain. The document that should talk first is a lab report from a state-certified laboratory. This page is how to read one before you spend money. It is not a substitute for your health department.
Get a report that counts
Private wells are not regulated, treated, or monitored the way public water systems are. CDC's guidelines for testing well water say to test at least once a year for total coliform bacteria, nitrates, total dissolved solids, and pH, to use a state-certified lab, and to ask your health department which other germs or chemicals matter where you live. EPA's private-well pages are the federal overview of that responsibility.
For iron staining and rotten-egg odor, also ask the lab for iron, manganese, and hardness, and ask whether they can report hydrogen sulfide and iron bacteria. A basic bacteria-and-nitrate panel will not size an iron filter. A strip from a hardware store will not either.
Numbers EPA actually publishes for stains and taste
EPA's secondary maximum contaminant levels are guidelines for public water systems. They cover taste, color, odor, and staining. EPA does not enforce them as health standards, and states may treat them differently. They do not regulate your private well. They are still the clearest official reference for why a fixture looks the way it does. The figures below are from EPA's secondary standards page and from 40 CFR 143.3.
| Line | Secondary guideline | How to use it |
|---|---|---|
| Iron | 0.3 mg/L | Above this, EPA describes rusty color, sediment, a metallic taste, and reddish or orange staining. It is not a health limit, and it is not the treatment capacity of any filter. |
| Manganese | 0.05 mg/L | Above this, EPA describes black to brown color, black staining, and a bitter metallic taste. A separate health advisory also exists. It is explained below. Neither number is a filter rating. |
| pH | 6.5 to 8.5 | EPA associates low pH with a bitter metallic taste and corrosion, and high pH with a slippery feel, a soda taste, and deposits. A filter's own operating range may be narrower. Use the manufacturer's range for equipment, and this range only as context. |
| Odor | 3 threshold odor number | EPA lists a rotten-egg smell as one example of odor, along with musty or chemical smells. This is not a hydrogen sulfide result in mg/L. Do not convert it into one. |
| Total dissolved solids | 500 mg/L | EPA associates higher levels with hardness, deposits, colored water, staining, and a salty taste. CDC also lists TDS on the yearly private-well panel. It does not tell you how much of the dissolved material is iron. |
Labs often print mg/L. For these dilute metals, mg/L and ppm are the same scale. If a column says µg/L, divide by 1,000 to get mg/L before you compare it with anything above. Hardness is a different unit problem: many reports use milligrams per liter as calcium carbonate, and softeners are often sold in grains per gallon. One grain per gallon equals 17.1 mg/L as calcium carbonate. Convert the units before you compare two quotes. Do not treat any hardness number on this page as a cutoff, because we are not publishing one.
Manganese: staining is not the same as the health advisory
The 0.05 mg/L secondary guideline is about stains and taste. In its 2004 drinking water health advisory for manganese, EPA also gives a lifetime health advisory of 0.3 mg/L. That document is guidance from 2004, not a diagnosis and not a private-well law. If your manganese result is high, take the report to your health department and read the advisory yourself. This site is not medical advice, and an iron filter is not a medical device.
Health lines: stop and call
Total coliform, E. coli, nitrate, arsenic, and lead are not reasons to shop for an iron filter. We are not reprinting numeric health limits here. Public-water standards live on EPA's drinking water regulations and contaminants page, and your state can be stricter. A number copied onto a blog, without your state's rule beside it, is how a website oversteps.
CDC says that if your well is or may be contaminated with harmful germs or chemicals, do not drink the water, and contact your health department. Use bottled water or another safe source until the well has been treated and tested again. An iron, sulfur, or manganese filter does not make that water safe.
The stain and odor lines, one at a time
Iron
Look for the word dissolved, ferrous, ferric, or total. Clear water that stains later is usually ferrous iron, which is the form air injection and chemical injection are built to oxidize. Rusty water at the tap means some iron is already a particle. The three treatment approaches depend on that distinction. Orange or brown staining is often iron, but manganese and iron bacteria can paint a similar picture. Do not buy on the color alone.
Manganese
Black staining can be manganese. Compare your result with the 0.05 mg/L secondary guideline for context, then compare it with the manganese limit on the filter sheet, which is a different kind of number. If the sheet has no manganese line, the sheet is incomplete for this complaint.
pH
Write this number next to the operating range on every filter you consider. If the lab pH is outside that range, the oxidation step may not work as the brochure describes. Ask about a pH correction step. Do not paper over it with a larger tank.
Hardness
Hardness is why people buy softeners. It is not an iron measurement. A softener is a poor iron filter and can foul when iron is high. If both numbers are up, plan on two jobs, in that order: iron and sulfur filtration inside a published limit, then softening if you still want it.
Hydrogen sulfide
Many routine panels skip it. The gas can leave the bottle before the lab opens it. If the rotten-egg smell is the reason you tested, ask for the lab's sulfide sampling method before you fill anything. EPA does not publish a secondary standard in mg/L for hydrogen sulfide. Do not invent one from the odor guideline. The rotten-egg guide separates a well problem from a water-heater problem.
Iron bacteria
This is often a separate presence-or-absence test, not a line in milligrams. Slimy rust, an oily sheen, or stringy growth in the toilet tank is the field clue. Iron bacteria are a nuisance group. They are not the same result as total coliform or E. coli. They are still a reason a normal iron filter may fail, and a reason to talk to a well contractor before you order media.
Tannins
Tea-colored water can be tannins. They can interfere with iron oxidation. If the water looks like weak tea even when iron is modest, ask the manufacturer whether the published limits assume tannin-free water.
A short worksheet
Copy these onto the report, in the margin, before you open a product page:
- Lab name and date.
- Total coliform and E. coli: present or absent. If present, stop and call.
- Nitrate, arsenic, lead, or any other health line the health department told you to order: flag them and do not hand them to an iron-filter quote.
- Iron, with the form if the lab stated it, in mg/L.
- Manganese in mg/L.
- pH.
- Hardness, with the unit written down.
- Hydrogen sulfide, or "not tested."
- Iron bacteria, or "not tested."
- Anything the sheet calls tannins, color, or odor.
Then use how to choose an iron and sulfur filter and the questions for SpringWell, US Water Systems, and SoftPro. The report picks the conversation. The website does not.