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Certified for What, Exactly
This is the single most useful idea on the subject and it takes one sentence: filters are certified against named claims, and the claims do not overlap the way people assume.
The takeaway
A water filter is certified against a named list of claims rather than against water in general. EPA names NSF/ANSI 53 for lead reduction, NSF/ANSI 42 Class 1 for the small particles that carry lead, and 53 or 58 for PFAS. A filter certified for one of those does nothing about the others.
Source: U.S. EPA, Choose the water filter that’s right for you; U.S. EPA, Identifying Drinking Water Filters Certified to Reduce PFAS.
What EPA names, and for what
EPA’s consumer guidance points at two marks on a box for lead: NSF/ANSI 53 for lead reduction, which it describes as reducing lead including dissolved lead, and NSF/ANSI 42 for particulate reduction at Class 1, which removes very small particles that may contain lead.
Its PFAS page names NSF/ANSI 53 for point-of-use systems claiming PFAS reduction and NSF/ANSI 58 for reverse osmosis systems.
Source: U.S. EPA, Choose the water filter that’s right for you; U.S. EPA, Identifying Drinking Water Filters Certified to Reduce PFAS.
Why the distinction is not pedantry
Because the failure mode is silent. A filter certified for something other than what you are worried about works perfectly, tastes fine, changes the water noticeably, and does not address the thing you bought it for.
There is no way to tell from the tap. The only place the answer exists is on the packaging and in the certification, which is why EPA points at the marks rather than at product categories.
Source: U.S. EPA, Choose the water filter that’s right for you.
What certification actually means
That the filter has been evaluated by an accredited third-party certification body against a published standard. For lead, EPA’s consumer tool covers filters meeting NSF/ANSI 53 and 42 that reduce lead to 5 parts per billion or less while achieving Class I particulate reduction.
An uncertified product making the same claim in marketing copy has had no such evaluation. The claim may be true. Nobody independent has checked it.
Source: U.S. EPA, Consumer Tool for Identifying Point-of-Use and Pitcher Filters Certified to Reduce Lead.
And one limit EPA states about its own standards
On PFAS specifically, EPA says current certification standards do not yet indicate that a filter will remove PFAS down to the levels EPA has now set for a drinking water standard, and that it is working to update certifications to match.
That sentence is from EPA rather than from us, and it is the most honest thing published on the subject. What follows from it.
Source: U.S. EPA, Identifying Drinking Water Filters Certified to Reduce PFAS.
Which is why the report comes first
You cannot match a certification to a problem you have not identified. The document that identifies it is published about your own system and costs nothing.
Read your report before you buy anything.It is published about your own system, it costs nothing, and it is the only thing that turns “I want a filter” into a question with an answer. If you do want something installed after that, we will route you to a contractor covering your area, matched on your ZIP code — you are never charged. Filtration is only our subject — every sort of plumbing job can be routed from here.
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