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Water Filter Rating Guide
Here are the water filter -specific requirements for meeting each level on the scale. Read on below for more details about terminology and specific examples. Read more about why I rate water filters and other products and materials here.
This guide covers how I rate water filters. It explains what all the little symbols mean under Shower Filters (and soon under Kitchen and Bath Filters).
I take into account what the water filter states it can remove, and whether that claim has been verified or not by a respected third party, self testing, or none at all.
To stay organized and unbiased, I use the Standard Rating Scale. For water filters, I only use the first three categories — healthiest, healthy, and minimal health risk. This is because that while some water filters aren’t doing what they claim, none should actively add harm. Here’s a quick reminder about what each level on the scale means:
Healthiest option available.
Healthy, but doesn’t meet the strict standards of the blue dot.
Minimal health risk. Verified to be healthier than its standard counterpart.
Caution is warranted.
Well-known harmful effect on health and should be avoided whenever possible.
Click on bolded statements to see links to research.
What contaminants are in tap water?
You might be surprised to know that tap water containing chemicals harmful to human health is not just limited to places like Flint, Michigan, or Erin Brockovich’s town of Hinkley, California. Pesticides, metals, plastics, pharmaceuticals, and more, easily find their way into the water supply all across the US. And, the chemicals used to disinfect the water from viruses and bacteria can leave behind harmful disinfection byproducts. Understandably, the EPA regulations and city water treatment practices have to take cost and politics into account (not just human health) when deciding what limits to set on these contaminants.
What is NSF?
It’s so boring— it stands for the National Sanitation Foundation. But it’s good that it’s boring! It is an independent, third party testing company that protects you, making sure that the claims a water filter company makes are true. NSF Certification means that NSF has tested the product, verified that the claims match the results, and can pop by anytime for a surprise inspection to make sure the quality stays high.
For water quality, the NSF has strict criteria for certification— for example, a filter must be able to reduce chlorine by 90% at a certain flow rate, for a certain number of gallons (typically 3 months worth of showering) for it to qualify for NSF-177 certification. If the filter only reduces chlorine by 80%, or can’t do it at a typical shower flow rate, it doesn’t qualify.
What does “tested to NSF standards” mean?
If you see the phrase “tested to NSF standards,” rather than “tested and certified by NSF,” this means the company has either tested the product themselves, sent it to a private lab, or sent it to a verified third-party lab that isn’t NSF, for testing. This happens for a few reasons:
NSF testing and certification can be expensive to maintain, and a start-up company may not have funding for this, even though their product is truly able to do what they claim. In this case, they may test it themselves, or send it to a less expensive private lab to show that it performs well. This may be done in good faith, or it may be done irresponsibly, and at less high of a standard than NSF would. That distinction, and whether or not you trust them, is up to you!
If a company’s water filter cannot meet NSF standards, they may purposely send it to a verified third party lab like WQA or IAPMO to gain verification that it comes close to meeting NSF standards, isn’t quite there, but still want to show transparency. For example, it’s very hard for a shower filter to meet both flow rate requirements set by states and filter out the NSF standard for PFAS. So, a brand may take their filter to WQA or IAPMO to show that while it doesn’t meet the NSF level, it still meets the highest level possible at a regular flow rate. WQA and IAPMO are both reputable third party testing labs that use standards similar to NSF to guide their work.
What is WQA?
WQA stands for the Water Quality Association. Their “Gold Seal” certification is actually the oldest third-party testing and certification program in the water treatment industry.
What is IAPMO?
IAPMO stands for the International Association of Plumbing & Mechanical Officials. Like NSF or WQA, they are a trusted third party lab that have long been a national standard in legitimate third party testing for water quality and protecting consumers.