What Water Filter Caps Filter PFAS? How to check
It’s boom time with water filters, since the EPA announced that nearly 10 percent of US water systems may have unsafe levels of PFAS, also known as “permanent chemicals,” in the water. Lead pipes are everywhere, even if they’re gone in Flint, Michigan, as of July 2025. Heck, there’s probably heavy metals in the groundwater, depending on where you are, and bottled water carries a lot of microplastics.
I’m not saying this to scare you. Your drinking water likely meets federal standards, and only about 4 percent of water systems end up with unsafe levels of contaminants, according to a 2020 EPA study. This means, local water systems will not have to comply with the new federal PFAS and PFOA standards for drinking water until 2031.
In response to concerns about the water supply, a whole new generation of water filters make amazing promises about reducing pollutants: chlorine, PFAS, heavy metals, pharmaceutical drugs like acetaminophen, fluoride if that worries you. Some of them are whole-home or under-sink reverse osmosis systems. Some simple countertop systems, gravity is installed with mesh or carbon or other filters.
So how do you decide which water claims are reliable? I have been testing water filters since 2024, often using chemical indicators and equipment, and I can attest that it is not always easy. Here’s a quick guide to checking out that water filter that caught your eye.
What are the NSF/ANSI Water Filtration Standards?
The first main sources of comfort for me when testing water filters are certifications and independent tests. Vague claims of 99 percent reduction in chlorine or PFAS or arsenic are hard to trust when the testing is in-house. To be credible, any third-party testing claims must clearly identify the lab that performed the testing.
The most reliable, high-quality method of certification is testing against NSF/ANSI standards. NSF, formerly the National Sanitation Foundation, is a Michigan-based non-profit, non-governmental organization founded in 1944 that develops and ensures compliance with a number of different testing standards—including those for water filtration. ANSI, or the American National Standards Institute, is an independent non-profit organization that accredits accrediting and testing organizations such as the NSF.
There are three main NSF/ANSI standards that apply to domestic drinking water filters.
- NSF-ANSI 42: Drinking Water Treatment Units—Effects of Aesthetics.
This ensures the removal of substances that are not considered harmful but may affect the makeup or taste of the water. This includes chlorine and chloramine used by cities to disinfect drinking water. - NSF/ANSI 53: Drinking Water Treatment Units—Health Effects
This ensures the removal of any number of compounds thought to be harmful, including lead, arsenic, PFAS, and others. Each compound is tested individually, among more than 50 pollutants. - NSF/ANSI 401: Emerging Compounds/Hazardous Contaminants
This ensures the screening of “emerging” compounds of potential concern, including pharmaceuticals, herbicides, and pesticides.
If you have an item in hand, these can be marked in a box. But don’t think that a certificate is a normal thing. Among shower water filters in particular, only one filter has received certification from the NSF for free chlorine removal: the Weddell Duo.
