"NSF/ANSI Standard 42 is for aesthetics, such as taste, smell and appearance (people often want to filter out traces of the disinfectant chlorine). Standard 53 focuses on safety, ensuring levels of lead or mercury, as well as some pesticides and industrial chemicals, are below the accepted limit. The certifications are for individual contaminants, and the product should specify all the contaminants it is approved to reduce." (Do Home Water Filters Work for PFAS and Other Contaminants? - NYT)
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Even though they are not federally enforced standards, it would be a good idea to get filters that are approved by them because it adds a layer of comfort knowing your drinking cleaner water.