Chromium-6 -- hexavalent chromium -- is the contaminant that made Erin Brockovich famous when it poisoned the groundwater in Hinkley, California in the 1990s. More than 25 years later, it contaminates water supplies for an estimated 200+ million Americans across all 50 states. And the federal government still has no specific drinking water limit for it.
That regulatory gap is finally closing -- slowly. Here's where things actually stand.
What Is Chromium-6?
Chromium exists in several forms. The most common are trivalent chromium (chromium-3) -- a naturally occurring micronutrient essential in small amounts for human metabolism -- and hexavalent chromium (chromium-6), a very different compound that is a known carcinogen when inhaled and a probable carcinogen when ingested in drinking water.
The EPA's current federal standard -- 100 ppb, set in 1991 -- applies to total chromium combined. It doesn't separately limit hexavalent chromium at all. The 100 ppb standard was set based on concern about skin reactions, before the evidence for chromium-6's carcinogenicity when ingested was fully developed.
Where It Comes From
Natural geology. The mineral chromite is found throughout US rock formations, particularly in the Southwest, Pacific Coast states, and parts of the Midwest. In oxidizing, alkaline groundwater conditions, chromium dissolves and migrates as chromium-6. This is the dominant source in most US cities -- Phoenix, Chicago, Pittsburgh, and others all have chromium-6 primarily from geological sources.
Industrial contamination. Chromium-6 is widely used industrially -- metal plating, anti-corrosion coatings, wood preservation, textile dyeing, and historically in natural gas pipeline cooling systems. Improper disposal contaminated specific locations, most famously Hinkley, California, where PG&E discharged chromium-6 into unlined evaporation ponds from 1952 to 1966. The Hinkley plume reached 580 ppb at some measurement points.
The Health Evidence
A 2008 National Toxicology Program study found significant increases in stomach and intestinal tumors in rats and mice that consumed chromium-6 in drinking water. In August 2024, EPA finalized its comprehensive IRIS Toxicological Review of Hexavalent Chromium, concluding that chromium-6 via oral ingestion is associated with cancer risk and that there is no clearly identified safe threshold level.
The American Chemistry Council disputes this conclusion, citing other international regulatory bodies that have concluded chromium-6 may operate via a threshold mechanism at typical drinking water concentrations. This scientific disagreement is genuine -- but the weight of independent evidence supports treating chromium-6 as a probable carcinogen at low doses.
The risk at typical US drinking water concentrations is not acute -- it's a small incremental increase in cancer risk from decades of cumulative exposure. Infants, children, people who take antacids regularly, and people with liver problems are considered more sensitive.
Where Regulation Stands in 2026
Federal level: There is still no specific federal MCL for chromium-6. Under a legal settlement agreement, the EPA is required to make a regulatory determination on a chromium-6 MCL by 2027. Whether the current administration will follow through is uncertain, but the legal obligation exists.
California: The only US state with a specific chromium-6 standard. California's chromium-6 MCL of 10 ppb went into effect on October 1, 2024. California's public health goal -- the level aimed at no more than one additional cancer case per million people over a lifetime -- is 0.02 ppb, 500 times lower than the enforceable standard.
EWG health guideline: 0.02 ppb -- matching California's public health goal.
Where your water likely stands: Most US tap water systems test between 0 and several ppb for chromium-6. Phoenix has averaged around 7--8 ppb in some testing periods. Chicago's water has shown around 0.19 ppb. Pittsburgh has shown around 0.535 ppb. All below the 100 ppb federal total chromium MCL. Many exceed the EWG guideline of 0.02 ppb.
Check your ZIP's chromium-6 levels at PureCity -- the EWG data for your utility will show what was actually measured.
Want to Know Your Chromium-6 Level?
Your utility's Consumer Confidence Report reports total chromium, not chromium-6 separately. For a full picture -- including chromium-6 specifically alongside lead, PFAS, disinfection byproducts, and 45+ other parameters -- the Tap Score Essential City Water Test is the most comprehensive and clearly reported option for municipal water users. Results come from an EPA/NELAC certified lab with a plain-English digital report. See our complete water testing guide for more on what to expect.
What Removes Chromium-6
Reverse osmosis removes chromium-6 with very high efficiency -- typically 85--97% rejection. It's the method EPA specifically identifies as most effective for chromium-6 removal.
What doesn't work: Standard activated carbon filters (Brita, PUR Standard, most pitcher filters), KDF/zinc-copper media, standard water softeners, and boiling (which actually concentrates chromium-6 slightly by evaporating water volume).
Some pitcher filters claim chromium-6 removal -- but verify with third-party certification. The Clearly Filtered pitcher independently certifies chromium-6 reduction. Most Brita filters do not.
Filters That Remove Chromium-6
- ✓NSF 58 certified -- 85-97% chromium-6 rejection plus lead, PFAS, arsenic, and DBPs
- ✓WQA Gold Seal; made in USA; proven decade-long track record
- ✓Most recommended under-sink RO across major review sites
- ✓~$50-70/year in replacement filters
- Requires one drilled faucet hole and basic plumbing connection
- 4:1 waste water ratio
- Not suitable for renters without landlord approval
The benchmark for chromium-6 removal at home. Addresses chromium-6 alongside every other major drinking water concern in one certified system.
- ✓Same chromium-6 rejection as standard RO -- 85-97%
- ✓6th alkaline stage restores minerals after RO removes them -- noticeably better taste
- ✓WQA certified; good for households who find flat RO water unappealing
- ✓Transparent filter housings for easy monitoring
- Slightly larger footprint than the APEC
- Higher price than the APEC ROES-50
- 4:1 waste water ratio
The upgrade pick if you want remineralized water alongside comprehensive chromium-6 removal. A good choice for Pittsburgh, Phoenix, or Atlanta residents who drink a lot of water at home.
- ✓Tankless design -- fits where traditional RO systems won't
- ✓NSF 42, 53, 58, and 372 certified -- high chromium-6 rejection
- ✓600 GPD flow rate; smart LED faucet shows filter life and TDS
- ✓2:1 pure-to-drain ratio -- more efficient than traditional RO
- Proprietary filter cartridges -- locked into Waterdrop replacements
- Higher upfront and annual filter cost than APEC
- Thinner long-term track record than APEC
The right pick if under-sink space is the constraint. Comparable chromium-6 removal in a significantly smaller footprint -- factor in the filter lock-in before committing.
- ✓Independently certified for chromium-6 reduction -- one of the only pitchers with this certification
- ✓Also certified for PFAS, lead, chloramine, fluoride, and 360+ contaminants
- ✓No installation required -- good for renters in affected cities
- ✓NSF 42, 53, 244, 401, and 473 certified
- Does not achieve the same chromium-6 reduction levels as RO
- Slower than a Brita -- around 10 minutes to filter a full pitcher
- Higher ongoing cost than standard pitchers
The best option for renters or anyone who can't install under-sink. Certified chromium-6 reduction plus comprehensive coverage -- far better than any standard carbon pitcher.
The Bottom Line
Chromium-6 is the "Erin Brockovich chemical" that affects far more Americans than most realize. The federal regulatory framework has been slow -- 30+ years after the problem was identified, a specific federal limit is still pending. California's 10 ppb standard (effective October 2024) is the leading-edge precedent.
In the meantime, if your utility's water shows chromium-6 above a few ppb and you want to reduce exposure -- especially if you have children, are pregnant, or have other risk factors -- an NSF-certified reverse osmosis filter at your kitchen tap is the most effective practical solution.
Related Articles
- How to Test Your Home's Drinking Water
- Pittsburgh, PA Water Quality 2026
- Phoenix, Arizona Water Quality 2026
- PFAS in Drinking Water
Sources: EWG: What Is Chromium-6? · EPA Chromium in Drinking Water · California State Water Board: Hexavalent Chromium MCL · EPA Final IRIS Toxicological Review of Hexavalent Chromium, August 2024 · NSF Certified Products Database