Filter Guides
NSF/ANSI 42, 53 and 401: What Fridge Filter Certifications Mean
Look at almost any refrigerator filter box and you will see “NSF certified” followed by a few numbers, usually 42, 53 and sometimes 401. Those numbers are not marketing fluff. Each one is a separate standard with its own test, and together they tell you what the filter has been independently proven to reduce.
Here is what each one means in plain English.
Who is NSF?
NSF is an independent organization that writes public health standards and tests products against them. For water filters, the standards are written with ANSI, the American National Standards Institute, which is why you see them written as NSF/ANSI.
A certified filter has been tested by an independent lab. Being certified is different from a brand saying its filter was “tested to” a standard, which can mean the company ran its own tests.
NSF/ANSI 42: taste, odor and appearance
Standard 42 covers what are called aesthetic effects, things that change how your water looks, smells and tastes but are not health related. The most common claim under Standard 42 is chlorine taste and odor reduction. Cities add chlorine to keep tap water safe as it travels through pipes, but many people do not like the taste.
It can also cover particulates, the tiny bits of sediment that make water look less clear.
NSF/ANSI 53: health-related contaminants
Standard 53 is the important one for health. It covers contaminants linked to health effects, and a filter has to prove it reduces each specific contaminant it claims. Depending on the filter, that can include:
- Lead, which can enter water from older pipes and fixtures
- Cysts such as Giardia and Cryptosporidium
- Some pesticides and herbicides
- Volatile organic compounds (VOCs) such as benzene
- Mercury and asbestos
One thing to remember: Standard 53 certification does not mean a filter removes everything on the list. It means the filter is certified for the specific contaminants named on its performance data sheet.
NSF/ANSI 401: emerging contaminants
Standard 401 covers what are often called emerging contaminants or incidental compounds. These are substances that show up in some water supplies at low levels and that people are increasingly concerned about. NSF lists up to 15 of them, including:
- Some prescription and over-the-counter drugs, such as ibuprofen and naproxen
- Certain herbicides and pesticides
- Flame retardants
- Chemicals like bisphenol A (BPA)
A filter certified to 401 has shown it reduces the specific compounds it lists from this group.
Why the contaminant count varies
You may see one filter advertised as reducing 28 contaminants and another 73. The number is simply how many specific substances that filter was certified for across all its standards. It changes from filter to filter, and even between versions of the same filter as new testing is done. For example, the packaging on everydrop Filter 1 and Filter 2 says 28 contaminants, Filter 3 says 73 and Filter 4 says 31.
A bigger number is not automatically better for you. What matters is whether the filter is certified for the contaminants you actually care about.
How to check a filter’s claims
- Read the performance data sheet. This document lists every contaminant the filter is certified to reduce and by how much.
- Search the NSF listings. NSF publishes a public database of certified products on its website.
- Look for the word “certified”. Be careful with phrases like “meets” or “tested to” without certification.
Where everydrop filters fit
everydrop Filters 1, 2, 3 and 4 are certified by NSF International under NSF/ANSI Standards 42, 53 and 401 for specific contaminant reduction. You can see the details for each on its product page: Filter 1, Filter 2, Filter 3 and Filter 4.
A certification only holds for the filter’s rated life, so keep an eye on the calendar too. Our guide on how often to change your filter explains why.