Under-Sink Water Filters and Reverse Osmosis: Prices and Certifications

An under-sink filter treats the water you drink and cook with, usually through its own faucet at the kitchen sink. Its line can also run to the refrigerator’s water dispenser and ice maker, or to more than one fridge. That’s where filtering pays off most: the U.S. Environmental Protection Agency’s (EPA’s) drinking water limits are built around the water people drink, and filtering it costs far less than filtering the whole house.

Three kinds

Under-sink carbon filters use one to three cartridges on the cold water line, feeding your kitchen faucet or a small separate one. They keep the minerals in the water and don’t waste any.

Under-sink reverse osmosis systems add a membrane to the cartridges, usually with a storage tank, their own faucet and a line to the drain. They remove far more, hardness included, and their line can also feed a refrigerator.

Countertop reverse osmosis units plug in and you fill them by hand. There’s no plumbing, so they suit renters, at the cost of counter space.

How reverse osmosis works

Water passes through a sediment filter and a carbon filter, then gets pushed through a membrane fine enough to hold back most dissolved minerals and contaminants. Clean water goes to a small tank or straight to the faucet; the water that carried away what the membrane held back goes down the drain. That’s the trade-off with RO: it removes more than carbon alone, and it uses more water to do it. Makers list how much in their specifications.

What they sell for

Store prices, read on November 4, 2026. Most of these show as sales against a higher list price.

Countertop units, for comparison:

Replacement filters are the running cost. Check their price and how often the maker says to change them before you compare systems.

Certifications to look for

A certification means an independent lab tested that model for a specific claim. The standards that matter here:

• NSF/ANSI 42: taste, odor and chlorine.
• NSF/ANSI 53: health contaminants such as lead, and PFOA and PFOS when the listing names them.
• NSF/ANSI 58: reverse osmosis systems.
• NSF/ANSI 401: a set of emerging contaminants, such as some medicines.

PFAS

11 of the 40 water systems we cover had at least one PFOA or PFOS sample above EPA’s limit in its 2023–25 testing. Those are samples, not compliance results, and utilities have until 2029 to meet the limit. If your city is one of them, a filter certified for PFOA and PFOS on the tap you drink from is where most households start. Our PFAS guide explains the limits, and each city page shows its results.

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Questions

Is an under-sink filter or reverse osmosis better?

They do different jobs. A certified carbon filter handles taste, chlorine and whatever it’s listed for, keeps the minerals and wastes no water. Reverse osmosis removes far more, including hardness, but sends some water down the drain and usually needs its own faucet. Pick by what’s in your water and what the filter is certified to remove.

Do under-sink filters remove PFAS?

Only models certified for it. In the NSF, WQA and IAPMO listings we checked, under-sink systems from Aquasana, Culligan, Kinetico and RainSoft are listed for PFOA and PFOS (two PFAS “forever chemicals”) reduction. Check the listing for your exact model number.

How much does an under-sink reverse osmosis system cost?

Online stores list them from $230 to $1,999, depending on brand, stages and whether there’s a storage tank. Replacement filters are an ongoing cost; check their price and schedule before you buy.

Can I install an under-sink filter myself?

Often, yes. Most connect to the cold water line under the sink, and many reverse osmosis (RO) systems need a hole for their own faucet and a connection to the drain. AquaTru, for one, says its under-sink unit involves drilling into pipes and recommends a professional. Countertop RO units need no plumbing at all.