Chromium-6 in Tap Water: What the EPA Standard Actually Measures
If a headline or your utility’s water report mentioned chromium-6 in tap water, you may have looked for the EPA standard for it. You won’t find a separate federal number. EPA’s enforceable limit is 0.1 milligrams per liter (mg/L), or 100 parts per billion (ppb), for total chromium, and that limit includes all forms of chromium, including chromium-6.
Two forms of one metal
Chromium is an odorless and tasteless metallic element. It occurs naturally in rocks, plants, soil, volcanic dust, and animals. In natural waters, the most common forms are trivalent chromium (chromium-3) and hexavalent chromium (chromium-6).
The two forms are not equally harmful. Chromium-3 is an essential human dietary element, found in vegetables, fruits, meats, grains, and yeast. Chromium-6, which EPA calls the more toxic form, can come from the erosion of natural chromium deposits and from industrial processes. EPA notes demonstrated instances of chromium being released to the environment by leakage, poor storage, or inadequate industrial waste disposal practices. ATSDR lists industries such as electroplating, leather tanning, and textile production, along with the burning of natural gas, oil, or coal. EPA’s contaminant table names discharge from steel and pulp mills as a drinking-water source.
In its 2012 public health statement, ATSDR reported that chromium had turned up at at least 1,127 of the 1,699 current or former NPL sites, the federal list of priority hazardous waste sites. The agency adds a caveat: a release does not always lead to exposure. For a wider look at how metals get into daily life, see WellOfNess’s piece on everyday sources of heavy metals.
Why does the rule count total chromium instead of chromium-6?
EPA covers both forms under one standard because they can convert back and forth in water and in the human body, depending on environmental conditions. In EPA’s words, measuring just one form may not capture all of the chromium that is present.
EPA then adds a cautious assumption. Its regulation assumes that a measurement of total chromium is 100 percent chromium-6, the more toxic form. Water systems are required to test for total chromium, not chromium-6 alone.
A chromium-6 result is a different measurement from the one the federal rule enforces. Compliance is judged against the 100 ppb total-chromium limit, and that limit already treats every bit of chromium as the more toxic form.
Which health effect is the 100 ppb limit based on?
The basis is skin reactions. The total chromium limit was established in 1991 and rests on the best available science at the time which indicated that continued exposure to chromium-6 could result in allergic dermatitis (skin reactions). EPA describes the standard as based on potential adverse dermatological effects over many years.
EPA’s national drinking water table shows that the enforceable limit and the health goal are the same. Under the Safe Drinking Water Act, MCLGs are non-enforceable health goals, based on possible health risks from exposure over a lifetime. Bottled water follows a matching benchmark: the FDA has determined that its chromium concentration should not exceed 0.1 mg/L.
Keep one limitation in mind: this number reflects the science available in 1991. ATSDR also stresses that whether chromium causes harm depends on the dose, the duration, the form (chromium VI as opposed to chromium III), and how you come in contact with it.
Is EPA revisiting the standard?
EPA says it began a rigorous and comprehensive review of chromium-6 health effects in 2008, based on new science. The agency is developing an Integrated Risk Information System (IRIS) assessment. That assessment will cover health effects from both breathing in and swallowing hexavalent chromium. A 2008 study by the National Toxicology Program will be part of that evaluation. When the review is done, EPA will decide whether the drinking water standard for total chromium needs to be revised.
In September 2010, EPA released a draft of the scientific human health assessment, the Toxicological Review of Hexavalent Chromium, for public comment and external peer review (19january2017snapshot.epa.gov). EPA said that once this human health assessment is finalized, it will carefully review the conclusions and consider all relevant information to determine if the current chromium standard should be revised (19january2017snapshot.epa.gov).
To learn how much chromium-6 is actually present in water systems, EPA required monitoring under the third Unregulated Contaminant Monitoring Regulation (UCMR 3). That rule required many but not all public water systems to monitor chromium-6 for a one-year period. As a result, your utility may or may not have chromium-6 data to share.
| Date | Event | Impact |
|---|---|---|
| 1991 | Total chromium MCL set | 100 ppb standard covers all forms of chromium, including chromium-6 and chromium-3 (epa.gov) |
| 2008 | EPA chromium-6 health review began | Could lead to a revised standard |
| 2008 | National Toxicology Program study | Included in EPA’s evaluation |
| Sept. 2010 | Draft Toxicological Review of Hexavalent Chromium released | Opened for public comment and external peer review |
| Sept. 2012 | ATSDR public health statement | Said EPA sought voluntary chromium-6 monitoring by municipalities |
Rules change, so ATSDR advises checking with the federal agency or organization that provides it for the latest status.
What happens if a water system goes over the limit?
EPA states plainly that if tap water from a public water system exceeds the federal standard, consumers will be notified. ATSDR also notes that you may have your water tested if you want to confirm you’re not exposed to high chromium levels.
If you’re new to home water testing, WellOfNess’s guide to testing tap water for lead covers how to work with your utility and certified labs for a related metal.
The federal rule caps total chromium at 100 ppb, treats all of it as chromium-6, and was originally set to prevent skin reactions. EPA’s review is meant to decide whether that 1991 limit still holds up against newer science.
Sources
- atsdr.cdc.gov – “Public Health Statement: Chromium” (2012)
- epa.gov – “Chromium in Drinking Water | US EPA” (2026)
- epa.gov – “National Primary Drinking Water Regulations | US EPA”
- wellofness.com – “Lead in Tap Water: How to Test It, and Why the Number to Beat Is Zero, Not 15 ppb” (2026)
- wellofness.com – “Where Heavy Metals Come From: Everyday Sources of Lead, Cadmium, Arsenic and Mercury” (2026)
- 19january2017snapshot.epa.gov – “Chromium in Drinking Water | Drinking Water Contaminants – Standards and Regulations | US EPA”