Chromium-6, also called hexavalent chromium or chromium(VI), is a form of chromium that can occur in groundwater naturally or enter water through industrial contamination.
The contaminant became widely known through the Erin Brockovich case in California, but chromium-6 is not limited to one town or one type of source of contamination.
It can occur naturally as groundwater interacts with chromium-bearing rocks, while industrial activities such as metal finishing, stainless-steel production, pigments, leather processing, and historical waste disposal have contributed to contamination in some locations.
Quick answer: The federal drinking-water limit applies to total chromium, not chromium-6 alone, and is currently 100 parts per billion (ppb). California has a separate chromium-6 standard of 10 ppb. Chromium-6 cannot normally be identified by taste, smell, or appearance, so water-quality reports and laboratory testing are the reliable ways to determine whether it is present.
In This Guide
- What Is Chromium-6?
- Chromium-3 vs. Chromium-6
- How Chromium-6 Gets Into Water
- Can You Detect It Yourself?
- Health Concerns
- Federal & California Standards
- California Compliance Timeline
- Municipal Water
- Private Wells
- When to Test
- Understanding Test Results
- Treatment Technologies
- Does Boiling Help?
- Where Berkey® Filtration Fits
- Frequently Asked Questions
What Is Chromium-6?
Chromium is a naturally occurring element found in rocks, soil, water, plants, and other parts of the environment.
It exists in several chemical forms, or oxidation states.
The two most frequently discussed in drinking-water and health conversations are:
- Chromium-3, or trivalent chromium
- Chromium-6, or hexavalent chromium
These forms behave differently chemically and toxicologically.
Chromium-3 vs. Chromium-6
| Characteristic | Chromium-3 | Chromium-6 |
|---|---|---|
| Other name | Trivalent chromium, Cr(III) | Hexavalent chromium, Cr(VI) |
| Occurrence | Occurs naturally in foods and the environment | Can occur naturally and can also result from industrial activity |
| Mobility in water | Generally less mobile under many environmental conditions | Can be relatively mobile in groundwater |
| Health context | Historically treated as an essential trace nutrient, although whether it is truly essential remains scientifically debated | Toxicological concern; EPA considers it likely carcinogenic through oral exposure |
Chromium-3 should not simply be described as a proven essential nutrient. U.S. dietary recommendations still include an Adequate Intake for chromium, but more recent research has questioned whether chromium deficiency produces a clearly defined physiological disorder.
How Does Chromium-6 Get Into Drinking Water?
There is no single source of chromium-6 in drinking water.
Natural Geology
Chromium occurs naturally in certain rocks and soils.
As groundwater moves through chromium-bearing geological formations, chemical reactions can release chromium into the water. Under some environmental conditions, part of that chromium can occur as chromium-6.
Industrial Activity
Hexavalent chromium compounds have been used in or associated with activities such as:
- Chrome and metal plating
- Stainless-steel manufacturing
- Pigment production
- Leather tanning
- Wood preservation
- Textile and dye processes
- Industrial waste disposal
Leaks, spills, contaminated soil, and historical disposal practices can allow chromium to enter groundwater.
Finding chromium-6 does not tell you where it came from. Identifying the source may require groundwater studies, geological information, historical land-use records, and environmental investigation.
Can You Taste, Smell, or See Chromium-6?
No reliable sensory test exists.
At concentrations typically discussed in drinking water, chromium-6 does not normally create a recognizable:
- Taste
- Odor
- Color
Water can therefore look and taste completely ordinary while containing measurable chromium-6.
Laboratory analysis is required to determine the concentration.
Clear water is not proof that chromium-6 is absent. Appearance, taste, and smell should never replace actual water-quality data for this contaminant.
What Do Researchers Know About Chromium-6 and Health?
The health effects of chromium depend strongly on its chemical form and route of exposure.
Hexavalent chromium has long been established as a human carcinogen when inhaled in certain occupational settings.
For drinking-water exposure, the evidence has evolved substantially.
EPA's current Integrated Risk Information System assessment concludes that chromium-6 is likely carcinogenic to humans through oral exposure, based primarily on human-relevant animal evidence.
Research has also evaluated potential effects involving:
- The gastrointestinal tract
- Liver
- Kidneys
- Blood
- Immune function
- Reproductive and developmental systems
The health significance of an individual water result depends on:
- Concentration
- Duration of exposure
- Water consumption
- Age and health
- Other exposure sources
Detection does not mean a particular person will develop disease. Risk assessment evaluates probability over time and across populations; it is not a prediction of an individual's outcome.
What Are the Current Drinking-Water Standards for Chromium?
The federal and California standards are different.
| Jurisdiction | Contaminant Regulated | MCL |
|---|---|---|
| Federal EPA | Total chromium | 100 ppb (0.1 mg/L) |
| California | Hexavalent chromium / Chromium-6 | 10 ppb (0.010 mg/L) |
Federal Standard
The U.S. Environmental Protection Agency currently regulates total chromium in public drinking-water systems at a Maximum Contaminant Level of 100 ppb.
Total chromium includes multiple chromium forms rather than measuring chromium-6 alone.
A total chromium result cannot tell you exactly how much chromium-6 is present. A separate chromium-6 analysis is needed if that specific form is the concern.
California Standard
California has a separate Maximum Contaminant Level for chromium-6 of 10 ppb.
The regulation became effective October 1, 2024.
California's Chromium-6 Compliance Timeline
An important detail missing from many summaries is that California did not require every public water system to comply on the same date.
| System Size | Compliance Date |
|---|---|
| 10,000 or more service connections | October 1, 2026 |
| 1,000–9,999 service connections | October 1, 2027 |
| Fewer than 1,000 service connections | October 1, 2028 |
California residents should distinguish between the rule's effective date and their utility's compliance deadline. The 10-ppb MCL became effective in 2024, but implementation is phased according to water-system size.
Chromium-6 and Municipal Drinking Water
If you receive water from a community water system, your utility monitors contaminants in accordance with federal and state drinking-water requirements.
Community water systems also provide customers with a Consumer Confidence Report, commonly called a drinking-water quality report.
Your report can help you understand:
- Your water source
- Detected regulated contaminants
- Measured levels
- Applicable standards
- Compliance information
However, chromium-6 may not always appear as a separate line item because federal regulation currently focuses on total chromium.
If you want chromium-6-specific information, contact your water utility or state drinking-water agency and ask whether separate monitoring data are available.
What About Private Wells?
Private wells are different because the homeowner is generally responsible for water testing and maintenance.
Chromium-6 testing may deserve consideration when:
- Local geology contains chromium-bearing formations.
- Nearby groundwater has previously shown chromium contamination.
- The property is near a historical metal-plating or industrial facility.
- A state or local agency identifies chromium as a regional concern.
- Previous testing detected total chromium.
For a broader testing strategy, see our Well Water Testing & Treatment Guide.
When Does Chromium-6 Testing Make Sense?
1. Review Existing Water Data
If you receive public water, start with your Consumer Confidence Report and your utility's published monitoring data.
2. Look at Regional Conditions
Check whether state agencies have identified naturally occurring chromium or industrial contamination in your area.
3. Determine Which Chromium Test You Need
Ask whether the laboratory is measuring total chromium, chromium-6 specifically, or both.
4. Use an Appropriate Laboratory
Chromium-6 testing requires laboratory methods capable of accurately measuring very low concentrations.
5. Interpret the Result in Context
Compare the results with applicable federal and state standards and discuss any unexpected results with the laboratory, utility, or the appropriate health or environmental agency.
Total Chromium vs. Chromium-6 Test Results
These measurements are not interchangeable.
Total Chromium
Total chromium measures the combined amount of chromium present in multiple chemical forms.
Chromium-6
A chromium-6-specific analysis measures hexavalent chromium separately.
If your question is specifically “How much chromium-6 is in my water?” a total chromium result alone cannot answer it.
Which Treatment Technologies Can Reduce Chromium-6?
Chromium-6 can be challenging because it occurs as a dissolved inorganic contaminant.
Treatment technologies used for chromium-6 can include:
- Ion exchange
- Reverse osmosis
- Specialized adsorptive media
- Reduction followed by precipitation or filtration in larger treatment systems
- Other engineered treatment processes
Performance depends on:
- Chromium concentration
- pH
- Water chemistry
- Competing ions
- Treatment-media capacity
- Flow rate
- System maintenance
Do not assume every carbon filter removes chromium-6. If chromium-6 is your concern, look for test data or certification covering the exact filter and contaminant.
For a broader comparison, see our Types of Drinking Water Filtration Systems Guide.
Does Boiling Water Remove Chromium-6?
No.
Boiling disinfects water but does not remove dissolved chromium-6.
As water evaporates, chromium remains behind, so prolonged boiling can increase its concentration in the remaining water.
See our Does Boiling Water Purify It? Guide.
Does a Standard TDS Meter Detect Chromium-6?
No.
A household TDS meter estimates the overall concentration of dissolved ionic substances by measuring electrical conductivity.
It cannot identify individual contaminants such as chromium-6.
A low TDS reading therefore does not prove that chromium-6 is absent.
Can Berkey® Filters Reduce Chromium-6?
Black Berkey® Elements have independent laboratory evidence specifically for Chromium VI (hexavalent chromium) reduction. The Black Berkey® test library identifies a County of Los Angeles Environmental Toxicology Laboratory test for Chromium VI, with reported reduction greater than 99.8% under the documented test conditions.
Phoenix Gravity New Millennium Edition™ Filter Elements also have current independent heavy-metal testing, but the published Phoenix summaries identify the tested analyte as chromium rather than specifically Chromium VI. In the April 2026 Atom Testing Laboratory report, chromium was challenged at 200 µg/L and measured at 7.2 µg/L after filtration, a calculated reduction of 96.4%.
| Filter element | What the current documentation supports | Important distinction |
|---|---|---|
| Black Berkey® Elements | Independent testing specifically identifies Chromium VI (hexavalent chromium), with a>99.8% reported reduction. | This is contaminant-specific independent laboratory evidence, not an NSF chromium-6 certification. |
| Phoenix Gravity New Millennium Edition™ | April 2026 independent testing reports chromium at 200 µg/L in influent and 7.2 µg/L in effluent, for a calculated reduction of 96.4%. | The published result is labeled chromium, so it should not automatically be represented as a chromium-6-specific result. |
Why the distinction matters: this article is specifically about hexavalent chromium. A laboratory result labeled only “chromium” does not establish how much of the challenge was Cr(VI) unless the underlying method or report explicitly identifies that species.
These results are independent laboratory evidence. They should not be described as NSF chromium-6 reduction certifications. Phoenix's current NSF listings concern NSF/ANSI 42 chlorine/taste-and-odor claims and NSF/ANSI/CAN 372 lead-content requirements, which are separate from chromium-6 reduction.
For the original laboratory documentation and current element-specific evidence, review our Berkey® Filter Test Results. If your system currently uses Black Berkey® Elements, use the Black-specific evidence for those elements. When replacement is needed, compare current Berkey® replacement filter options and evaluate the evidence for the exact element you plan to use.
If laboratory testing has confirmed elevated chromium-6 in your water, verify treatment with chromium-6-specific performance data whenever possible. Do not substitute a total-chromium result, a generic heavy-metal claim, or an unrelated NSF certification for contaminant-specific evidence.
Review the evidence before choosing a filter
Start with your chromium-6 test result, then compare it with the documented performance and test conditions for the exact filter element you use or plan to purchase.
Review Berkey® Filter Test Results | Compare Replacement Filters
Frequently Asked Questions About Chromium-6
What is chromium-6?
Chromium-6, or hexavalent chromium, is a chemical form of the element chromium. It can occur naturally in certain geological environments and can also result from industrial activity.
Is chromium-6 the same as chromium?
Chromium is the element. Chromium-6 is one chemical form of chromium. Other forms include chromium-3.
Is chromium-6 the same as total chromium?
No. Total chromium measures multiple forms of chromium together, while a chromium-6 test measures hexavalent chromium specifically.
What is the federal drinking-water limit for chromium-6?
EPA currently does not have a separate federal MCL specifically for chromium-6. The federal MCL for total chromium is 100 ppb.
What is California's chromium-6 limit?
California has established a chromium-6 Maximum Contaminant Level of 10 ppb, or 0.010 mg/L.
When does California's 10-ppb chromium-6 rule take effect?
The regulation became effective October 1, 2024, but compliance deadlines are phased by system size through October 2028.
Does chromium-6 cause cancer?
EPA's current toxicological assessment concludes that chromium-6 is likely carcinogenic through oral exposure, based primarily on animal evidence relevant to humans. Individual risk depends on dose and duration of exposure.
Can chromium-6 occur naturally?
Yes. Groundwater can acquire chromium through interactions with chromium-bearing rocks and soil. Industrial contamination is therefore not the only possible source.
Can I taste chromium-6 in water?
No reliable taste, odor, or visual clue identifies chromium-6 at typical drinking-water concentrations.
How do I test water for chromium-6?
Use a laboratory that offers hexavalent-chromium analysis. Be clear that you want chromium-6 specifically rather than only total chromium.
Should I test my private well for chromium-6?
Testing is particularly warranted where local geology, historical industrial activity, nearby contamination, or previous water tests indicate that chromium could be a concern.
Does boiling remove chromium-6?
No. Boiling does not remove dissolved chromium-6 and can concentrate dissolved substances as water evaporates.
Does activated carbon remove chromium-6?
Ordinary activated carbon should not automatically be assumed to reduce chromium-6. Some finished filters combine carbon with other media and may have chromium-specific test results. Evaluate the exact product.
Can reverse osmosis reduce chromium-6?
Reverse osmosis can reduce dissolved chromium when the system is appropriately designed and maintained. Verify chromium-specific performance for the exact product.
Can a TDS meter tell me if chromium-6 is present?
No. TDS meters cannot identify individual contaminants such as chromium-6.
Does a Consumer Confidence Report show chromium-6?
It may show total chromium because that is federally regulated. Separate chromium-6 data may or may not appear, so contact your utility if you need contaminant-specific monitoring information.
Is chromium-3 a beneficial mineral?
Chromium-3 has historically been treated as an essential trace nutrient in U.S. dietary guidance, but more recent research has questioned whether chromium is truly essential because a clearly defined deficiency state has not been established.
Can Black Berkey® Elements reduce chromium-6?
Yes. Independent laboratory documentation for Black Berkey® Elements specifically identifies Chromium VI and reports greater than 99.8% reduction under the evaluated test conditions. This is independent laboratory evidence, not an NSF chromium-6 certification.
Do Phoenix Gravity elements have chromium-6-specific test data?
Current published Phoenix testing documents chromium reduction, including a 2026 result of 200 µg/L influent to 7.2 µg/L effluent. Because the published analyte is identified as chromium rather than specifically Chromium VI, this article does not present that result as chromium-6-specific evidence.
Final Thoughts
Chromium-6 is a good example of why drinking-water questions often require more detail than simply asking whether a contaminant is “present.”
You need to know:
- Which form of chromium was measured
- The concentration
- Which federal or state standard applies
- Whether your water source is municipal or private
- Whether treatment has been tested for chromium-6 specifically
For public-water customers, the best starting point is the local Consumer Confidence Report and utility monitoring information. For private-well households, laboratory testing may be useful when local geology or land-use history raises concerns.
The key principle is simple: chromium-6 cannot be diagnosed by taste or appearance, and a generic “water filter” claim is not enough. Use actual water data and contaminant-specific filter performance when deciding what, if anything, your household needs.