Chromium-6 (hexavalent chromium) is the form of chromium made famous by the “Erin Brockovich” case. There is no federal MCL specific to chromium-6 — it’s regulated only as part of total chromium, with a combined limit of 0.1 mg/L (100 ppb). California set its own state MCL for hexavalent chromium specifically (0.010 mg/L) in 2024. The absence of a dedicated federal limit is itself worth knowing, not something to gloss over.
What actually removes chromium-6
- Reverse osmosis (NSF/ANSI 58) — a membrane process effective against chromium-6 along with a wide range of other dissolved contaminants.
- Activated carbon (NSF/ANSI 53) — but only carbon media specifically certified for hexavalent chromium reduction, not general-purpose carbon filtration.
What doesn’t work
Most consumer carbon pitchers and faucet filters are certified only for chlorine taste and odor (NSF/ANSI 42) and have not been tested against hexavalent chromium at all. Because chromium-6 has no federal MCL, some products make vague “reduces heavy metals” claims without a specific certification backing them up for this contaminant — that phrasing is not the same as an NSF/ANSI 53 listing that names hexavalent chromium by name. Standard water softeners (cation exchange for hardness) are not designed to remove chromium-6.
How to choose
- Look specifically for “hexavalent chromium” or “chromium VI” named on the product’s NSF/ANSI 53 or 58 certification documentation — “chromium” alone can refer to the less-toxic trivalent form, which is a different removal target.
- If you’re in California, check your water system’s compliance status against the state’s own 10 ppb hexavalent chromium limit, since the federal total-chromium limit alone doesn’t reflect that stricter state standard.
- Chromium-6 in groundwater is often tied to industrial discharge (steel and pulp mills, electroplating, leather tanning) or natural geologic sources — knowing which is more likely in your area can help gauge whether ongoing monitoring, not just one-time filtration, makes sense.
Test before you buy
Chromium-6 has no color, taste, or odor at the concentrations of concern, and because it isn’t part of routine reporting everywhere (no federal MCL to test against outside states like California), a certified lab test that specifically analyzes for hexavalent chromium — not just total chromium — is the only way to know your actual exposure before buying a filter.