Chromium-6, also called hexavalent chromium or Cr(VI), is one of the most widespread heavy metal contaminants in US tap water. The Environmental Working Group estimates it’s detectable in the water of more than 200 million Americans, including residents of Phoenix, Los Angeles, Hialeah, Riverside, and most cities in the southwestern United States. If the name sounds familiar, it’s because chromium-6 is the contaminant at the center of the 2000 film Erin Brockovich — the real-world case involved Pacific Gas & Electric contaminating groundwater in Hinkley, California, leading to the largest direct-action lawsuit settlement in US history.
Despite the scale of the problem, the EPA has not set a federal Maximum Contaminant Level (MCL) for chromium-6 specifically. Federal law regulates total chromium (Cr(III) plus Cr(VI)) at 100 parts per billion, but does not require utilities to report chromium-6 separately. California is the only state with an enforceable chromium-6 standard, set at 10 ppb in 2014 (and later suspended in 2017).
What chromium-6 is and where it comes from
Chromium-6 is a heavy metal compound used industrially in chrome plating, stainless steel manufacturing, leather tanning, textile dyes, anti-corrosion coatings, and wood preservation. It enters drinking water through three main pathways:
Industrial contamination. Historic industrial sites, particularly in California, the Midwest, and the Rust Belt, leached chromium-6 into groundwater over decades. Cleanup at these sites is ongoing.
Natural geological deposits. Some bedrock formations naturally contain chromium that becomes mobile when groundwater conditions change. This is the primary source in the desert Southwest, where chromium-6 levels are highest.
Treatment plant chemistry. Water utilities that disinfect using chlorine can inadvertently convert chromium-3 (the less harmful trivalent form) to chromium-6 during treatment. This is a known mechanism but not the primary driver of contamination.
Why chromium-6 is dangerous
The National Toxicology Program classified chromium-6 as a “known human carcinogen” in 2008 based on extensive animal studies and human occupational exposure data. Long-term ingestion of chromium-6 in drinking water is associated with stomach cancer and gastrointestinal tumors. The California Office of Environmental Health Hazard Assessment set a Public Health Goal of 0.02 ppb — the level at which lifetime cancer risk is one in a million.
EWG’s health guideline matches this: 0.02 ppb. Detected levels in US tap water frequently exceed this guideline by 10-100x or more. For example:
- Phoenix, AZ: typical 0.5 ppb (25x EWG guideline)
- Los Angeles, CA: typical 0.18 ppb (9x EWG guideline)
- Tampa, FL: typical 0.08 ppb (4x EWG guideline)
- Norman, OK: among the highest US detections, occasionally above 10 ppb
These levels are below the now-suspended California limit of 10 ppb. They are not federally illegal, because there is no federal limit. But they are well above what cancer-risk modeling suggests is safe.
Why isn’t there an EPA limit on chromium-6?
The short answer: regulatory inertia, industry pushback, and cost. The EPA has been studying chromium-6 since 1991 and acknowledges its toxicity, but setting a federal MCL requires the EPA to demonstrate both a health benefit and feasibility of meeting the limit at reasonable cost. Industry stakeholders (particularly in the chrome plating, leather, and chemical industries) have argued the costs of compliance would be prohibitive.
A federal MCL for chromium-6 has been “under consideration” through multiple administrations. As of 2026, no firm rulemaking date has been announced.
How to know if chromium-6 is in your tap water
Three options:
Check your utility’s TapWaterSafety page. We pull EWG data on chromium-6 detection per utility and flag it as a Top Concern when present. If your utility shows chromium-6, you’ll see it on the contaminants table with its detected level versus EWG’s 0.02 ppb guideline.
Read your utility’s CCR. Some utilities voluntarily report chromium-6 alongside total chromium. Most do not. Lack of reporting in a CCR does not mean lack of contamination — it means the utility isn’t required to test for it.
Get your tap water tested. Mail-in lab tests from EPA-certified labs run $80-200 for a chromium-6 test. SimpleLab’s Tap Score and similar services include it in heavy metals panels.
How to filter chromium-6
Standard carbon filters do not remove chromium-6. This is a critical point. Brita, basic refrigerator filters, and most pitcher filters certified only for NSF/ANSI 42 (chlorine reduction) will not protect you from chromium-6.
Two technologies that do work:
Reverse Osmosis (most effective)
Reverse osmosis membranes physically block chromium-6 molecules. RO systems typically remove 95-99% of chromium-6. This is the gold standard for chromium-6 protection.
NSF/ANSI Standard 58 specifically tests for chromium reduction in RO systems. Look for this certification when buying.
Strong-base anion exchange resin (less common at home use)
Some specialized filtration cartridges use anion exchange resin to selectively capture chromium-6. These are less common in consumer products but are used in commercial water treatment.
Top filter recommendations for chromium-6
Best countertop option (no plumbing required): AquaTru Countertop Reverse Osmosis. NSF/ANSI 58 certified, removes chromium-6 along with arsenic, lead, PFAS, and 80+ other contaminants. Especially good for renters who can’t install a permanent system. $449-599.
Best under-sink option (permanent installation): Aquasana OptimH2O Reverse Osmosis + Claryum. Same NSF/ANSI 58 certification, plus an added carbon stage for taste. Dedicated drinking water faucet. $429-549.
Whole-house option (advanced): If you have specifically severe chromium-6 contamination, a whole-house RO system is possible but expensive ($2,000-5,000 installed). Almost always overkill — chromium-6 is dangerous through ingestion, not skin contact, so point-of-use filtration at the kitchen tap is sufficient.
What does NOT remove chromium-6
- Basic carbon pitcher filters
- Most refrigerator filters
- “Alkaline” or “ionized” water systems
- Water softeners (these address calcium and magnesium, not chromium)
- Boiling water (concentrates chromium-6 rather than removing it)
- Distillation works in theory but is impractical for daily home use
Who should be most concerned
Chromium-6 risk accumulates with exposure duration. The highest-priority populations to filter are:
- Families with young children (developing bodies are more sensitive to carcinogens)
- Pregnant residents
- Long-term residents of areas with documented contamination (Phoenix, LA, the Inland Empire of California, parts of Oklahoma)
- People with already-elevated cancer risk
For healthy adults in areas with low detection levels (less than 5x EWG guideline), the absolute risk is relatively small. The cost-effectiveness argument favors a reasonable filter regardless.
The bottom line
Chromium-6 is a known human carcinogen with no federal drinking water limit, present in the water of over 200 million Americans, and impossible to remove with standard carbon filters. If your water utility shows chromium-6 detection on its TapWaterSafety page, a reverse osmosis system at your kitchen tap is the practical solution.
Find your water by ZIP code to see if chromium-6 is detected in your utility and get a filter recommendation matched to your specific water.