Chromium in Well Water: The Public 0.1 mg/L Line

By SubcontractorHub Editorial Team·Published October 2026

Chromium in well water shows up as a printed metal, not as a color you can trust and not as a hardness number. USGS describes a trace element as one found at less than 1.0 milligram per liter, and it names chromium in that group along with arsenic, cadmium, copper, lead, mercury, nickel, and zinc. Being on that list does not set the drinking-water line. The line used here is the public MCL. SubcontractorHub is an all-in-one sales and project management platform for solar, roofing, and HVAC contractors. A water dealer uses the same idea: one job record, one unit, no second number invented in the driveway.

Chromium in Well Water Is a Total on This Table

Read the parentheses. The contaminant name is chromium (total). Customers may have heard a hexavalent story from a news report. The table fetched for this article does not print a separate hexavalent MCL. If you write a second limit, you are no longer quoting the table.

Lead is a different metal with its own public action level, covered in lead in well water. Barium is a different row, covered in barium in well water. Do not average them, and do not let a softener sized for hardness stand in for a metal the lab actually reported.

The Public 0.1 mg/L Line, and Who It Governs

The source is EPA's national primary drinking water regulations page. That page says the primary standards apply to public water systems. A private well is outside that sentence unless the state brings the number across. Say so on the quote. The overview of that gap is private well water regulations.

Allergic dermatitis is the potential health effect the table lists for long-term exposure above the MCL. It is not a rash you diagnose, and it is not proof that a particular well caused a skin problem. If a customer is asking about symptoms, the next person is a clinician. Your next job is still to read the lab correctly.

Chromium in Well Water When the Lab Uses Micrograms

USGS Circular 1209 states that one thousand micrograms per liter equals 1 milligram per liter. So 0.1 mg/L is 100 µg/L. A lab that prints 40 µg/L is not “40” against a limit of “0.1.” It is 0.04 mg/L against 0.1 mg/L.

The scale, and why trace metals often arrive in micrograms while minerals arrive in milligrams, is milligrams and micrograms. The arithmetic is the microgram milligram converter. Do the step on the job, not in your head at the door.

Selenium has the same unit trap at a different public number. That article is selenium in well water. Uranium is often already in micrograms. Neither result is a chromium result. File them on their own lines.

Sources the Table Names, and Sources It Does Not

The row lists discharge from steel and pulp mills, and erosion of natural deposits. That is a national source list. It is not a finding that this house sits downhill from a mill. If the customer asks “where did it come from,” say what the table says, then say you do not know their pathway from the number alone.

Plumbing corrosion is on other rows, such as lead and copper. Do not borrow that sentence for chromium unless the chromium row said it. This one did not. A first-draw versus flushed pair can still be useful when you are trying to see whether the metal is in the pipes or in the aquifer, but that is a sampling plan you write down. It is not a conclusion this page already made.

What This Page Will Not Sell

No treatment is named, because the row does not name one. No removal percentage is stated. A reverse-osmosis percent from a different contaminant, or a softener claim from a hardness visit, does not transfer. If a manufacturer's listing names chromium for a specific model, that listing is the document. This article is not that listing.

NSF/ANSI numbers are not a rank. How to read a listing is NSF/ANSI water treatment standards. The device covers the taps you plumb it to. The other taps do not change because one sink was treated.

How to Write the Chromium Line on the Job

1. Copy the number and the unit. Do not round micrograms into a story.
2. Convert to mg/L if the lab used µg/L, and show 100 µg/L as the public 0.1 mg/L mass.
3. Label 0.1 mg/L as the public total-chromium line, not as a private-well statute you did not check.
4. Say the row is total chromium. Do not add a hexavalent limit the table did not print.
5. Name the taps. Retest those taps after any work, and keep both sheets.

The place this metal sits among the other tests is the well water testing guide. The water treatment workflow should hold the lab, the unit conversion, and the quote together. A text message that says “chromium was high” will be read three ways on the next visit.

Who Should Ignore a Guess From This Page

If the state health department has a private-well chromium instruction, follow that instruction. If a listing or a design manual names a process for a specific form of chromium, follow that document and say which form the lab reported. This page is the habit of reading total chromium, the public 0.1 mg/L line, and the unit. It is not a medical opinion and not an equipment schedule. A blank chromium line stays blank.

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