Hexavalent chromium appears on water paperwork as chromium-6, Cr(VI) or hexavalent chromium, and a filter claim lines up with a report only when both describe that same chromium form in the same unit. Two documents show how a claim keeps the forms apart. The NSF listing for the A.O. Smith AORO-50 carries "Chromium (Hexavalent) Reduction" and "Chromium (Trivalent) Reduction" as separate claims, and the AquaTru Carafe performance data sheet gives each form its own row with a challenge level, a pass line and reduction figures.
The two documents belong to different products and show different fields: the listing shows which chromium forms the AORO-50 is claimed for, and the Carafe sheet shows how the Carafe was tested for each form. The earlier roundup of water filter brands for hexavalent chromium removal explains the regulation and the treatment technologies, and the background on checking an NSF certification for a specific model covers directory searches in general.
Which Chromium Form a Report Line Measures
Chromium can be reported in three ways, and each answers a different question. Total chromium adds every form together, while the two form-specific lines split it into hexavalent chromium, Cr(VI), and trivalent chromium, Cr(III), the form California's State Water Resources Control Board describes as "a required nutrient."
The rules behind those lines differ by level of government. The EPA's drinking water regulations set a single federal MCL of 0.1 mg/L for "Chromium (total)." California, according to the State Water Board, keeps its own total chromium MCL of 50 µg/L and, since October 1, 2024, adds a separate hexavalent chromium MCL of 10 µg/L. A California report can therefore carry two chromium lines, each against its own limit.
That difference sets the matching rule. A hexavalent chromium line calls for a claim that names the hexavalent form. A trivalent chromium claim answers a trivalent question only, even when it sits on the same document as a hexavalent one.
The Other Metals on the Same Report Page
On a utility report, a chromium line sits among the metals and other inorganic chemicals, so lead, arsenic or copper figures can sit on the same page. For those neighboring lines, the Viomi M1, a tankless under-sink RO system that adds minerals back after filtration, is SGS-tested to reduce lead by more than 99.87%. Its SGS test report, which refers to NSF/ANSI 58-2023, gives lead, arsenic, cadmium, mercury, copper, barium and selenium each a row with the water going in, the water coming out and a reference figure, all in mg/L, measured at the start of filter life and again after 14,600 liters (about 3,857 US gallons).
Lead shows how those rows read: 0.1680 mg/L went in and less than 0.0002 mg/L came out at the start of filter life, against a reference figure of 0.005 mg/L. Written in µg/L, that outlet is below 0.2 µg/L.
Micrograms, Milligrams and the Pass Line in a Claim
California writes its chromium limits in µg/L, while the EPA table and NSF-style data sheets use mg/L, and 1 mg/L equals 1,000 µg/L. Putting every figure in one unit before reading them side by side avoids treating a number as a thousand times larger or smaller than it is.
| Figure | As printed | In mg/L | In µg/L |
|---|---|---|---|
| California hexavalent chromium MCL | 10 µg/L | 0.010 | 10 |
| California total chromium MCL | 50 µg/L | 0.05 | 50 |
| EPA total chromium MCL | 0.1 mg/L | 0.1 | 100 |
| Carafe hexavalent chromium challenge water | 0.3 mg/L, plus or minus 10% | 0.3 | 300 |
| Carafe maximum permissible product water | 0.1 mg/L | 0.1 | 100 |
The last row needs the most care. On the Carafe sheet's hexavalent chromium row, the pass line is the highest product-water concentration allowed during the test, 0.1 mg/L. California's hexavalent chromium MCL, at 0.010 mg/L, is a tenth of that. The two numbers do different jobs: the pass line is a test condition the product had to meet with spiked water, and the MCL is the limit a utility reports against. Writing them down on separate lines, each with its unit, keeps one from standing in for the other.
The same unit care applies to a household's own number. A report line of 20 µg/L, used here as an example, is 0.020 mg/L, which is the form to use when setting it beside a data sheet written in mg/L.
How the Two Documents Keep Hexavalent and Trivalent Apart
The first thing that separates the two forms is the claim name. On the NSF directory, the AORO-50, a plumbed-in reverse osmosis model listed with replacement module S1448RS, has one line for "Chromium (Hexavalent) Reduction" and another for "Chromium (Trivalent) Reduction," so a Cr(VI) report line corresponds to the first of the two. A listing of this kind records which claims exist and which module belongs to the system; it does not print challenge levels or reduction percentages.
The second is the test behind each name, where the two forms can differ even on one product. The Carafe sheet, which covers models AT100, AT110, AT120, AT130 and AT140, challenges both forms at 0.3 mg/L against the same 0.1 mg/L maximum product water, yet the tolerance is plus or minus 10% for hexavalent chromium and plus or minus 30% for trivalent chromium. The results differ as well: a 90.1% minimum and 97.5% average reduction for the hexavalent form, compared with 99% and 99.6% for the trivalent form. Different tolerances and different results on a single sheet are the reason one form's number cannot be borrowed for the other.
The sheet also sets maintenance separately from the test rows: the RO membrane, SKU 10AT100RF01, is replaced "every 24 months or 600 gallons, whichever comes first." That is a replacement schedule, recorded on its own line next to the chromium figures.
A Consistency Check for Chromium Claims
Each row is one field to record, with the report value and the document value kept on separate lines.
| Field to record | What a matching claim shows | Where it appears in the two documents above | What to write down |
|---|---|---|---|
| The form named (hexavalent, total or trivalent) | The same form, by name | Separate claim lines on the AORO-50 listing; separate rows on the Carafe sheet | Form on the report and form in the claim |
| The unit (µg/L or mg/L) | Any unit, converted to match | mg/L on the Carafe sheet | Both numbers in mg/L |
| Your concentration | The challenge level and its tolerance | 0.3 mg/L, plus or minus 10% (0.27 to 0.33 mg/L), for hexavalent chromium on the Carafe sheet | Your value and the challenge range on separate lines |
| The limit your utility reports against | The pass line, read as a test condition | 0.1 mg/L maximum permissible product water | Both figures, labeled separately |
| The models covered | The model names in the document | AT100, AT110, AT120, AT130 and AT140 on the Carafe sheet; AORO-50 on the listing | The model names as the document prints them |
| Replacement parts and schedule | Part numbers and intervals | Module S1448RS with the AORO-50; for the Carafe, membrane 10AT100RF01 every 24 months or 600 gallons, whichever comes first | Part number and the date or gallon count it falls due |
The tolerance row is easy to misread. "Plus or minus 10%" describes the range the challenge water was allowed to fall in, from 0.27 to 0.33 mg/L for the Carafe's hexavalent row. It is a description of the test setup, so a report value goes in its own cell beside it rather than being treated as inside or outside the test.
What a Matched Chromium Claim Tells You
A matched claim shows that the filter document and the utility are describing the same chromium: the same form by name, set in the same unit, tied to a named model and its replacement part. For a hexavalent chromium line, that means a document that names the hexavalent form on its own line. Everything else in the record, from the challenge water to the pass line and the maintenance schedule, adds detail to that match without changing it.
FAQ
Do chromium-6, Cr(VI) and hexavalent chromium mean the same thing?
All three name the same form of chromium. Trivalent chromium, Cr(III), is the other form, and total chromium counts both together, so a report or a filter document that names one of these is answering that question specifically.
Why is the pass line in a chromium claim higher than California's limit?
On the Carafe sheet, 0.1 mg/L is the maximum product water allowed in the hexavalent chromium challenge at a nominal 0.3 mg/L, plus or minus 10%. California's 10 µg/L is a regulatory limit for public water systems. They describe different things, which is why they are recorded on separate lines.
What does "plus or minus 10%" next to the challenge concentration mean?
It is the permitted range of the test water. For the Carafe's hexavalent chromium row, that range runs from 0.27 to 0.33 mg/L, and the trivalent row allows plus or minus 30%, from 0.21 to 0.39 mg/L.
How does a replacement module relate to an NSF listing?
The directory names the replacement module on the same line as the listed model, as S1448RS appears beside the AORO-50, and notes that replacement modules are components. That pairing identifies which part belongs to the listed system.
Which unit should a chromium comparison use?
Either unit works as long as every figure uses the same one. Converting µg/L to mg/L means dividing by 1,000, so California's 10 µg/L hexavalent chromium MCL becomes 0.010 mg/L, the unit the Carafe sheet uses.
Where does a household find the chromium figures for its own water?
The EPA requires community water systems to deliver an annual drinking water quality report, the Consumer Confidence Report, which covers the regulated contaminants found in local drinking water. In California, the hexavalent chromium MCL of 10 µg/L has applied since October 1, 2024, alongside the state's 50 µg/L total chromium MCL, so both kinds of line can appear on a California system's report.
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