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Faucet water filters treat the water at one tap. Most use carbon to improve taste and smell, and what else a model removes depends on what it is certified for, so read the label before you buy.

I have not installed or tested any filter. This comes from the CDC, NSF, the EPA and the Brita and PUR support pages, named where each claim appears.

What a Faucet Filter Does, and What It Does Not

The CDC says water filters can improve the taste of water, its safety, or both, and that a filter removes things based on the size of its pores, the size of the substance and the substance’s electric charge. It also warns that filters remove beneficial chemicals too, such as the chlorine that kills germs and the fluoride that prevents cavities, so a filter is not automatically an upgrade. Source: CDC, About Choosing Home Water Filters.

The CDC adds that most home filters, such as pitcher and fridge filters, are not designed to remove germs. They typically use a carbon filter to make water taste better or to remove heavy metals such as lead. PUR says the same about its faucet systems: PUR does not filter microbes. If you have a weakened immune system, the CDC says to talk to your healthcare provider and a water disinfection specialist about whether to get a system, to look for one that removes Cryptosporidium if you do, and to avoid changing filters yourself.

Types of Faucet Water Filters

These are the technologies the CDC, NSF and EPA describe. Which of these a particular faucet model uses is not covered by the sources I read, so check the maker’s product page and performance data sheet before you rely on any of them.

I left out alkaline and ionizing faucet filters because I found no CDC, NSF or EPA source that describes them.

What the NSF Numbers Mean

NSF says no federal regulations exist for residential water treatment filters, purifiers and reverse osmosis systems, so voluntary standards fill the gap. It also says the numbers reflect the order the standards were developed and are not a ranking. Source: NSF Standards for Water Treatment Systems.

NSF’s warning is the useful part: certification to a standard does not mean a filter reduces all possible contaminants. Check that the filter is certified for the specific contaminant you care about, and look the product up in the NSF database the CDC points to.

For parasites, the CDC says to look for NSF standard 53 or 58 certification for cyst reduction or removal, or an absolute pore size of 1 micron or smaller. It explains that a filter with a nominal or mean pore size of 1 micron will let some larger particles through, which is why the label wording matters.

Do You Need a Filter?

The CDC says that if your tap water does not contain harmful germs or chemicals, you may not need a filter. It also says taste, smell and appearance are not reliable indicators, because harmful germs and chemicals often do not change them, while harmless substances such as some sulfur compounds can make water taste or smell bad.

• Public water: the CDC says your utility must provide a water quality report every year, and it shows whether harmful germs or chemicals are in your water. The EPA has a page to find your local Consumer Confidence Report.
• Private well or rain water: the CDC says to test at least once a year, and to contact your health department about what to test for and a state-certified lab.
• PFAS: the EPA says to ask your water provider first, and that a filter may not be useful if PFAS are absent or below federal limits. If you do want one, it points to NSF/ANSI 53 or 58 certification for PFAS reduction, and says that, as of April 2024, certification standards did not yet indicate that a filter would remove PFAS down to the levels the EPA has now set.

Faucet-Mount Filters: What the Makers Say

A faucet mount attaches to the end of the tap and, in the CDC’s terms, is a point-of-use filter that delivers filtered water to a single tap. Brita and PUR both publish support pages, and their numbers are the best guide to upkeep because they are the manufacturers’ own. Sources: Brita faucet setup, Brita faucet FAQ and PUR faucet FAQ. PUR’s support page lists both horizontal and vertical faucet systems and gives each its own installation video.

How to Install One

Brita says installation is easy and needs no tools, and its steps and PUR’s are close to the same. Neither set of steps I read mentions plumber’s tape or the shut-off valve under the sink.

• Remove the aerator from the faucet, and its washer. PUR suggests a rubber jar opener or a rubber band around it if it is stuck.
• Check the threading. Inside threads use an adapter; outside threads likely do not. Brita says you may need to try different adapter and washer pairings, and PUR says to try the unit first and then each adapter in turn, finger-tightening only.
• Mount the base on the faucet. No tools are needed.
• Click the filter in while supporting the base. Brita says not to force the cartridge.
• Switch to the filtered setting and flush with cold water for 5 minutes, per Brita. Brita says this removes carbon dust and activates the filter, and that the 100-gallon life begins after the flush. Brita suggests using the flush water on houseplants.

If the unit and all three adapters do not fit, PUR says to contact it for help rather than forcing anything.

Care and Replacement

PUR says to clean the outside of the housing with a damp sponge or soft cloth, and that a mild dishwashing liquid may also be used. It warns that using anything else could damage the unit, so I would not soak the housing in vinegar. Brita says that if the system has not been used for several days, run water through the filter for 30 seconds to wet and reactivate it.

To change a Brita cartridge, press the release button at the back of the filter cup, pull the cartridge up, align the groove with the indicator, push until it clicks, and flush for 5 minutes. The CDC adds that you should wear gloves when changing a filter and wash your hands afterwards, and that regular changes according to the maker’s instructions help prevent germs growing in the filter. The EPA says the same for PFAS filters: they only work when maintained according to the manufacturer’s instructions.

Other Ways to Filter

The CDC groups faucet-mounted filters and under-sink filters as point-of-use filters, good if you only need to filter water you drink and cook with. Whole-home filters, also called point-of-entry filters, treat all your water. The CDC cautions that a whole-home filter that removes chlorine or other disinfectants can let more germs grow in your plumbing. If your faucet is a pull-out or handheld type, a faucet mount may not fit, and an under-sink filter is the other point-of-use option.

NSF lists water softeners under their own standard, 44, separate from standards 42 and 53, which cover adsorption filters such as carbon. If scale from hard water is what you are fighting in a kettle or coffee maker, see how to descale an electric kettle and coffee maker descaling.

Frequently Asked Questions

Do faucet filters remove bacteria and viruses?

Usually not. The CDC says most home filters are not designed to remove germs, and PUR states that its filters do not filter microbes. The CDC says bacteria need an absolute pore size of 0.3 micron or smaller, ultrafiltration, nanofiltration or reverse osmosis, and viruses need nanofiltration or reverse osmosis.

How often should I replace a faucet filter?

Brita says every 100 gallons, about 4 months, for its FF-100 and SAFF-100 faucet systems, and more often with hard water. PUR says after 100 gallons or every 3 months. Both makers also build in a filter change light, so follow your model’s manual.

Can I use a faucet filter on any tap?

No. PUR says its systems fit most standard faucets but not pull-out or handheld faucets, and Brita says an adapter is needed for inside threads. If none of PUR’s supplied adapters fits, it says to contact its support. An under-sink filter is the alternative.

Do I need a water filter at all?

Maybe not. The CDC says that if your tap water has no harmful germs or chemicals you may not need one. Read your utility’s annual water quality report, or test a private well at least once a year, and choose a filter for the specific substance you find.

Does a filter remove PFAS?

Only if it is certified for it. The EPA says to look for NSF/ANSI 53 or 58 certification for PFAS reduction, but its page says that as of April 2024 certification standards did not yet show removal down to the levels it has now set. Ask your water provider first.

Does reverse osmosis remove fluoride?

The CDC says reverse osmosis may reduce fluoride, along with arsenic, nitrate and other substances, and that you should check the label for the specific chemicals a filter can remove. It also notes that fluoride prevents cavities, so removing it is a trade-off.

How This Guide Was Put Together

This is a research-based guide. I read the CDC page on choosing home water filters, NSF’s explanation of its standards, the EPA pages on PFAS filters and Consumer Confidence Reports, and the Brita and PUR faucet support pages. I could not read Brita’s printed user guide, so Brita’s numbers come from its support pages.

This guide does not say what Brita’s or PUR’s faucet models are certified to reduce; that is on each model’s performance data sheet, so check the sheet for your model. I did not find a neutral source for how much water reverse osmosis wastes, so this guide gives no figure.

If you are ready to pick a model, my best faucet water filter guide compares specific units by price, rating and owner complaints.