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NSF/ANSI 244: Backup germ filtration

Official title: Supplemental Microbiological Water Treatment Systems - Filtration

Covers filters for water that is already treated or shown to be safe. They guard against occasional, accidental germ contamination, such as before a boil-water advisory.

What it can cover

  • Bacteria, with at least a 3-log (99.9%) reduction (WQA listing claim: "Bacteria")
  • Viruses, with at least a 3-log (99.9%) reduction (WQA listing claim: "Virus")
  • Cysts (WQA listing claim: "Cyst")

What it does not

  • Water that has not been treated or shown to be microbiologically safe
  • Chemical contaminants such as lead or PFAS

The usual mistake

Calling a 244 filter a purifier. It is a backup for water that is already safe. Products meant to make germ-contaminated water safe are certified under NSF/ANSI 55 Class A or NSF P231.

The fine print

  • Products must have an end-of-life indicator.
  • NSF's own listing search had no 244 category on Oct. 4, 2026, while WQA lists 244 products with Bacteria, Cyst and Virus claims.
  • NSF posted a 2026 edition of this standard.

Sources

  1. NSF Standards for Water Treatment Systems, NSF. Checked Oct. 4, 2026.
  2. NSF/ANSI 244 Technical Requirements, NSF. Checked Oct. 4, 2026.
  3. Search for NSF Certified Drinking Water Treatment Units (standards and reduction claims lists), NSF. Checked Oct. 4, 2026.
  4. Joint Committee on Drinking Water Treatment Units: recent documents (2026 editions of 44, 55, 62, 244, 401), NSF. Checked Oct. 4, 2026.
  5. Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.