Water Filter Comparison
...The Question of Filter Certification

Filter Certification

The American National Standards Institute (ANSI) has accredited three testing organizations to test water purifiers according to their standards: 1) The Water Quality Association (WQA), 2) The Underwriters Laboratories (UL), and 3) The National Sanitation Foundation International (NSF) These are independent organizations which test water filters to see if they do what they claim.

The National Sanitation Foundation International (NSF) is highly respected in the world of water filter certification. To have the NSF seal of approval is a great achievement for a water filter. But what does filter certification really mean? It's important to understand the standards and the meaning of the filter certification given. This seal of certification is one of the most valuable criteria for choosing a filter. If it doesn't have NSF certification, I personally wouldn't even consider it. It's possible it's a good filter, but how do I know?

What are the Standards of Certification?

NSF/ANSI Standard 42: Drinking Water Treatment Units - Aesthetic Effects (This certifies that the filter reduces the non-health related contaminants such as chlorine and other tastes and smells to a specific level.)

NSF/ANSI Standard 53: Drinking Water Treatment Units - Health Effects (This standard addresses the effective reduction of a long list of health related contaminants such as Cryptosporidium, Giardia, lead, volatile organic chemicals, etc.)

NSF/ANSI Standard 58: Reverse Osmosis Drinking Water Treatment Systems (Standard 58 is designed particularly for RO systems to verify reduction of the kinds of contaminants they remove such as fluoride, hexavalent and trivalent chromium, total dissolved solids, nitrates, etc.)

NSF/ANSI Standard 44: Cation Exchange Water Softeners (This standard verifies the filter's ability to reduce hardness in the water and can verify its ability to reduce radium and barium.)

NSF/ANSI Standard 55: Ultraviolet Microbiological Water Treatment Systems (This sets standards relates to the destruction of microorganisms in water. There are two classes of UV systems: Class A is designed to disinfect and remove microorganisms, such as bacteria and viruses, from contaminated water to a safe level. Class B is a system designed to supplement bactericidal treatment of public drinking water or other drinking water which has been deemed acceptable by a local health agency.)

NSF/ANSI Standard 62: Drinking Water Distillation Systems (This standard is designed specifically for distillation systems verifying the reduction of specific contaminants such as total arsenic, chromium, mercury, nitrate/nitrite, and microorganisms from public and private water.)

NSF/ANSI Standard 177: Shower Filtration System - Aesthetic Effects (This certifies the reduction through a shower filter of free available chlorine that may be present in the water.)

What is the Meaning of Certification?

A manufacturer claims that their filter can remove a list of specific contaminants. NSF is a neutral third party which uses rigorous standards and methods for testing that filter to see if it really does remove those specific impurities. For the impurities that pass the reduction test, it issues its NSF "seal of approval" saying, "This filter effectively reduces these contaminants."

If they've met the reduction standard for lead, for example, that means they have the "seal of approval" for reducing lead to an acceptable level. You can see that one filter might effectively reduce one health-related contaminant and another effectively reduces 15 health-related contaminants and both get to claim NSF seal of approval for Standard 53. So look closely at what has been tested and verified.

A second question that needs clarification is what does the term "reduced" mean? When NSF says a filter "reduces" lead in the water, what does that mean? Is it reduced to a specific level or is it "reduced" in a relative sense meaning "lowered the amount of"?

Let me try to clarify. The Environmental Protection Agency (EPA) has set two standards for each contaminant. One is called the MCL or the Maximum Contaminant Levels and the other is the MCLG or the Maximum Contaminant Levels Goal. The first is what is required of public water utilities and the second is the ideal level they should be aiming at. The public water utility is required to inform the public on each contaminant and if they don't reach the MCL for a contaminant they must point it out to the public in their annual water quality report.

It is this former standard, the MCL or Maximum Contaminant Levels standard that NSF International is testing water filters against for filter certification. They introduce high levels of that contaminant into the water and then test the filter to see if it reduces that contaminant to the MCL of that impurity. If the filter claims to work for 500 gallons before changing it, they run all 500 gallons, testing periodically to be sure that contaminant is reduced to the MCL level continuously up till the last of the 500 gallons.

All this is done for your benefit so you can be sure that the filter you are buying is effectively reducing the contaminants they claim to be reducing.

How to Use Certification in Choosing a Filter

1. Is the filter that you are looking at NSF Certified? (Check the NSF web site to see. Because of the complexities of finding information and understanding the information on the NSF site, I have prepared a page on NSF to simplify the process, if you need it. Go to "NSF.org Made Easy". Also beware of misleading advertising. One I read recently says, "Tested to Standard 53". It turns out that it is not a filter certification by NSF and it doesn't say who tested it.)

2. Which standard is it certified for? (See the different standards listed above.)

3. Which contaminant or contaminants has the filter been certified to reduce? (Note that Standard 42 has to do with taste and odor, not health related contaminants. Standard 53 relates to the reduction of health related contaminants.)

4. Are these the contaminants you are concerned about?

5. How many contaminants are effectively removed by this filter according to NSF? (In general, the more contaminants removed the more costly the filter. All filters are not created equal! Some give no health protection, others give a little health protection, and others give a lot of health protection and yet they all "filter" your water. The question is, are they filtering out what you need filtered out?)

For additional information on filter certification and other issues to consider in comparing filters check our discussion of "How to Choose a Water Filter".