NSF/ANSI 42 vs. 53 vs. 401: what the numbers actually mean

The rule that prevents most mistakes

A filter certified to a standard is not automatically certified for every possible claim within that standard. Always match the exact filter model to its performance data sheet or certification-directory listing.

NSF/ANSI 42: aesthetic effects

Standard 42 covers non-health-related effects such as chlorine taste and odor and particulate claims. It can be useful for taste and clarity, but the exact claim still varies by product.

NSF/ANSI 53: health-effect claims

Standard 53 covers specific health-effect reduction claims. Common examples include lead, cysts, VOCs and chromium, but a product must be listed for the particular claim.

NSF/ANSI 401: emerging or incidental compounds

Standard 401 addresses selected emerging compounds detected at trace levels, including certain medications, herbicides and chemical compounds. It does not mean every product reduces every compound covered by the standard.

How WaterFilterSpecs reports certification

We separate manufacturer statements from direct certification-directory or performance-sheet verification. Missing data is labeled as missing; it is never filled by inference.

• Exact part number
• Named standard
• Named contaminant claim where available
• Source and review date
• Evidence grade