Water Filter Cartridges: How to Check Certification and When to Replace

Filter cartridges look alike, but they remove different things. This guide uses NSF International's consumer page on home water treatment.

Read the certification claim

NSF says the numbers such as 42 and 53 "refer to the standard to which the filter has been certified." It advises looking on the packaging for a claim of specific contaminant reduction, for example lead. NSF also states that manufacturers choose which contaminants their product will reduce, and that NSF verifies the filter will do what it says it will do. A filter that is not certified for a contaminant should not be assumed to remove it.

The page does not describe what each standard covers, so check the listing. Not verified: the scope of each numbered standard; look at the certified listing.

Verify the listing

NSF directs readers to its certified-product search for point-of-use and whole-house products. Search for the exact model of the cartridge, not just the housing.

Replacement

NSF says a treatment system needs regular maintenance, and filters must be replaced when required. Some have indicator lights, others list replacement time ranges. Budget for the ongoing cost of replacement cartridges when comparing models. An overdue cartridge may stop doing its job. Not verified: exact replacement intervals; follow the manufacturer's manual.

Know your water first

If you are on a private well, test the water first. Our Minnesota and Wisconsin articles list tests recommended by state agencies. A filter chosen without a test can miss the real problem.

Questions to ask a dealer

Which contaminants is this exact cartridge certified to reduce?
How do I confirm the listing?
What is the cartridge price and replacement schedule?
Does the housing fit other brands of cartridge?

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General information only. Not electrical, plumbing, legal or code advice. Confirm details with a licensed professional and your local authority.