A filter jug on the counter. A blue light on the lid. What did it just remove? This guide is for people choosing a home water filter who want to know what the labels mean.

The CDC (page dated 10 April 2024) says most home filters, like pitcher or fridge filters, are not designed to remove germs and typically use a carbon filter to make water taste better or remove heavy metals like lead. It says pitcher and fridge filters often use activated carbon, mainly to improve taste and smell rather than safety, and that many filters do not remove germs. What a filter removes depends on pore size and electric charge, and some germ-removing filters do not remove chemicals, and the reverse.

Quick answer

  • Per the CDC, most pitcher and fridge filters are not designed to remove germs.
  • What a filter removes depends on its pore size and the substance; check the label for specific substances.
  • NSF Standard 42 is taste and odor, 53 cyst reduction, 58 reverse osmosis and 62 distillation.
  • Test your water first: you may not need a filter.

Germs, by filter type (CDC)

  • Parasites (Giardia, Cryptosporidium; also the ameba Naegleria fowleri): certified to NSF Standard 53 or 58 for cyst reduction or removal, an absolute pore size of 1 micron or smaller, or microfiltration, nanofiltration, ultrafiltration or reverse osmosis.
  • Bacteria (Salmonella, E. coli): an absolute pore size of 0.3 micron or smaller, or ultrafiltration, nanofiltration or reverse osmosis.
  • Viruses (norovirus, hepatitis A): nanofiltration or reverse osmosis.

"Absolute" means every pore is at or below the stated size. "Nominal" or "mean" is only an average.

The marks

The CDC describes NSF International as an independent organization that develops public health standards for products. Look for its certification on the label: Standard 42 (taste and odor), 53 (cyst reduction), 58 (reverse osmosis) and 62 (distillation). The CDC says you can look up specific products in the NSF database to see what they are certified to remove.

Lead and chemicals

The CDC says reverse osmosis filters remove some types of chemicals, including lead, copper, chromium, chloride and sodium, and may also reduce others such as arsenic and fluoride. It says filters that remove germs often do not remove chemicals, and vice versa, so check the label for the specific substances a filter removes. It also says taste, smell and appearance are not always good indicators of water safety.

Do you need one?

The CDC says to test your water and choose a filter that removes the germs or chemicals you are concerned about, and that if your tap water has no harmful germs or chemicals you may not need a filter. For tap water from a public system it points to the annual water quality report; for a private well or rainwater system it advises testing at least once a year. It also notes that some filters remove beneficial chemicals such as chlorine or fluoride. If you have a weakened immune system, it advises talking to a healthcare provider and not changing filters yourself.

Upkeep

The CDC says to maintain any filter, changing it on the manufacturer's schedule, wearing gloves and washing your hands afterward. We make no claim that any filter makes water "safe". These are US sources.

What to check before you buy

  • The specific germs or chemicals the label says it removes.
  • An NSF certification, looked up in the NSF database.
  • Whether pore size is 'absolute' or only 'nominal' or 'mean'.
  • The maker's schedule for changing the filter.

Last checked: 21 October 2026. General information, not legal, medical or financial advice. Sources: CDC, About choosing home water filters (page dated 10 April 2024; read 21 October 2026).