Under-Sink Water Filters: How to Choose

Short answer: Find out what is in your water first, then choose an under-sink unit that is certified to reduce that specific contaminant.^{Source [1]Source [3]} Carbon units are cheaper and are often certified for chlorine taste, lead and some chemicals. Reverse osmosis (RO) units reduce a wider range, including nitrate, arsenic and fluoride, but cost more, need more upkeep and send some water down the drain.^{Source [2]Source [5]} Whatever you buy, change cartridges on schedule, because a neglected filter can stop working or make water worse.^{Source [1]}

An under-sink filter treats water at one faucet, usually the kitchen tap, where you drink and cook. The Minnesota Department of Health (MDH) calls these point-of-use units a good option for drinking and cooking water.^{Source [1]} This guide covers how to decide whether you need one, which certifications to look for and what upkeep costs.

Step 1: Find out whether you need one

MDH says most Minnesotans don't need home water treatment, and that you should test your water before buying a unit.^{Source [1]} If you're on public water, your utility publishes an annual Consumer Confidence Report that lists what was detected.^{Source [8]} If you're on a private well, a lab test is the only way to know what is there. Our guide to reading your water report walks through those reports, and the lead testing guide covers lead in particular.

Testing first matters because no single unit removes every contaminant.^{Source [1]} A filter that improves chlorine taste may do nothing for nitrate, and a unit sold for "purer" water may not be certified for the one problem you have.

Step 2: Match the certification to your contaminant

There are no federal regulations for home water filters, so certification is how you check a claim.^{Source [3]} NSF's standards are numbered in the order they were written, not by quality.^{Source [3]} The ones that matter most for under-sink units:

Source: NSF.^{Source [3]}

A standard number on the box isn't enough. Certification covers specific contaminants, so check the model's listing to see exactly which reductions it is certified for.^{Source [3]Source [4]} MDH says to look for certification from NSF, UL or the Water Quality Association, and EPA also lists CSA and IAPMO as certifiers.^{Source [1]Source [5]}

For lead

EPA's advice is to use a filter certified to remove lead and to replace the cartridge on time.^{Source [6]} Its consumer tool says to look for a point-of-use filter certified to reduce lead to 5 parts per billion or less, with Class I particulate reduction, under both NSF/ANSI 53 and NSF/ANSI 42.^{Source [7]} Run only cold water through the filter, and don't count on boiling, which doesn't remove lead.^{Source [6]}

For PFAS

EPA lists activated carbon, ion exchange and reverse osmosis as filter types that can reduce PFAS, and under-sink systems as one point-of-use option.^{Source [5]} Look for certification under NSF/ANSI 53 or 58 for PFAS.^{Source [5]} EPA also notes a limit: certifications as of April 2024 don't yet show reduction to the levels in its newer PFAS drinking water standards.^{Source [5]} MDH says its own study found granular activated carbon removes PFAS.^{Source [2]}

Step 3: Choose between carbon and reverse osmosis

Most under-sink units are either carbon filters or RO systems. Here is how they compare, using MDH and EPA figures.

Sources: MDH (2017 quotes and 2018 research) and EPA (last updated November 2025).^{Source [2]Source [5]}

The cost ranges are wide because they span very different products, and the MDH figures are several years old. Use them for scale, not as current prices.

Carbon is the simpler choice when your concern is chlorine taste or a contaminant the specific model is certified for, such as lead.^{Source [2]Source [7]} MDH warns that bacteria can grow in carbon filters and that a saturated filter can release contaminants back into the water.^{Source [2]}

Reverse osmosis makes sense when your test shows something carbon isn't certified for, such as nitrate or arsenic.^{Source [2]} The tradeoffs are higher cost, wastewater, regular membrane and cartridge changes, and sometimes a pretreatment step to keep the membrane from clogging.^{Source [2]Source [5]} Our reverse osmosis pros and cons guide goes into more detail.

Step 4: Compare under-sink with other options

An under-sink unit sits between a pitcher and a whole-house system:

• Pitchers are also point-of-use treatment and need no plumbing.^{Source [2]} See how to choose a water filter pitcher.
• Under-sink units treat water at one tap, usually the kitchen faucet. MDH lists them as point-of-use treatment.^{Source [1]}
• Whole-house (point-of-entry) systems treat the water entering the home, and MDH's cost estimates for them run much higher than for point-of-use units.^{Source [2]} See the whole-house water filter guide.

If your concern is only drinking and cooking water, MDH suggests a point-of-use unit is a good fit.^{Source [1]}

Step 5: Install, test and maintain

• Test after installing. MDH recommends testing the treated water to confirm the unit is working.^{Source [1]}
• Change cartridges on schedule. EPA says filters only work if they are maintained.^{Source [5]} MDH warns that unmaintained units lose effectiveness and can make water quality worse.^{Source [1]}
• Use cold water. EPA advises against running hot water through a filter.^{Source [6]}
• Budget for replacements. MDH estimates carbon replacement filters at $10 to $100 every few months, about the same range as the unit itself, and RO upkeep at $100 to $200 every one to two years.^{Source [2]}

Write the install date on the housing or set a phone reminder, because cartridge life depends on how much water you use.

What under-sink filters can't do

• One unit won't fix everything. MDH says no single treatment removes all contaminants.^{Source [1]}
• Certification has limits. A certified model is only certified for the contaminants on its listing.^{Source [3]Source [4]}
• PFAS certification lags the newest limits. EPA says certifications as of April 2024 don't yet show reduction to its newer standard levels.^{Source [5]}
• It treats one tap. Bathroom faucets and showers stay untreated.

Frequently asked questions

Do I need an under-sink water filter?

Not always. The Minnesota Department of Health says most people on public water don't need home treatment. Read your water utility's annual report or test a private well first, then filter if a contaminant you care about shows up.

Is reverse osmosis better than a carbon under-sink filter?

It depends on the contaminant. Reverse osmosis reduces a wider range, including nitrate, arsenic and fluoride, but costs more and sends some water down the drain. Carbon filters cost less and can be certified for chlorine, lead and some chemicals. Match the certification to your problem.

What certification should an under-sink filter have for lead?

EPA says to look for a filter certified to reduce lead to 5 ppb or less under NSF/ANSI 53, plus Class I particulate reduction under NSF/ANSI 42. Check the specific model in the certifier's listing.

Do under-sink filters remove PFAS?

Some are certified to. EPA points to activated carbon, ion exchange and reverse osmosis units certified under NSF/ANSI 53 or 58. EPA notes that certifications as of April 2024 don't yet show reduction to its newest PFAS limits.

How often should I change an under-sink filter cartridge?

Follow the manufacturer's schedule. Carbon cartridges are often changed every few months, and reverse osmosis membranes and cartridges on longer cycles. An overdue filter can stop working and may let bacteria grow.