KDF (copper-zinc media)

KDF is a trade name for granules of high-purity copper and zinc. Its maker says KDF 55 reduces chlorine and water-soluble heavy metals, and KDF 85 reduces iron and hydrogen sulfide.

In home systems KDF is almost always a layer next to activated carbon, not a treatment on its own. Its best-supported role is chlorine reduction, and it is common in shower filters. Most other claims made for it are uncertified at the system level.

How it works

The maker describes KDF as a redox (oxidation-reduction) medium: as water passes over the copper-zinc granules, free chlorine is chemically converted to chloride rather than simply trapped. It says KDF 55 works “even in hot water.”

KDF’s own materials describe it as targeting inorganic contaminants, while activated carbon targets organic ones. That split is the reason KDF is “often used in combination with other filtration systems, such as carbon filters,” in the maker’s words. You will find it:

• As the top layer of a whole-house tank, as in Aquasana’s Rhino and SpringWell’s CF1.
• As a separate cartridge, as in Express Water’s WH300SCKS, which pairs KDF with catalytic carbon.
• Inside shower filters.

What it removes and what it does not

• Chlorine: the claim with the most support. The maker says KDF 55 carries an NSF certification to NSF/ANSI 42.
• Iron and hydrogen sulfide: maker claims for KDF 85. None of the whole-house KDF systems we track is certified for either. For real iron or sulfur problems, see air injection oxidation.
• Heavy metals such as lead: a maker claim. SpringWell lists heavy metals for its CF1’s KDF layer without certification. For lead, choose a filter certified to NSF/ANSI 53 for lead.

It does not remove:

• PFAS and VOCs. These are organic chemicals, which is the carbon’s job, not the KDF’s.
• Nitrate. No KDF maker claim covers it.
• Bacteria, in the sense that matters for safety. The maker says KDF “controls” bacteria and algae, and Aquasana describes the KDF in its Rhino as bacteriostatic. That limits growth inside the filter. It is not disinfection of contaminated water.

The maker also claims KDF controls scale. That is not the same as removing hardness.

Certifications to look for

The maker lists NSF certifications for its media: KDF 55 to NSF/ANSI 42, and KDF 85 to NSF/ANSI/CAN 61, the materials safety standard. These cover the raw media, not the finished filter you buy. A brand saying it “uses NSF-certified KDF” has not told you anything certified about its own system.

What to look for instead:

• NSF/ANSI 42 on the finished system, naming chlorine reduction.
• NSF/ANSI 177 for shower filters. It covers free available chlorine only, and NSF notes certified shower filters have not been evaluated in the presence of chloramine.
• NSF/ANSI 53 for any health claim, such as lead.

Check the model number in the NSF, IAPMO or WQA listings.

Installation and upkeep

KDF layers inside a whole-house carbon tank need no drain or power and are replaced along with the carbon. As a cartridge, Express Water replaces its three-filter set, including the KDF stage, every 6 to 12 months or 100,000 gallons. Shower filters attach to the pipe just in front of the showerhead and are replaced on the maker’s schedule.

Costs

KDF is rarely priced on its own. Prices checked September 2026:

System	Where the KDF is	Price
Express Water WH300SCKS	KDF and catalytic carbon cartridge	$548 system; $99.99 KDF cartridge; $186.99 three-filter set every 6 to 12 months
Aquasana Rhino	Top tank	$999
SpringWell CF1	Layer above catalytic carbon	$1,160

Paying extra for a KDF stage makes sense mainly for chlorine taste or smell, especially in the shower. It is not a substitute for a certified filter if you are treating a health contaminant. Compare systems in the product finder and best filters for city water.

Pros and limits

Pros

• Reduces chlorine, including in hot water.
• Needs no drain, power or chemicals.
• Pairs well with carbon, which handles organic chemicals.

Limits

• Iron, sulfur, metal and bacteria claims are maker claims, not system certifications.
• Does nothing for PFAS, VOCs or nitrate on its own.
• Media certifications are often presented as if they covered the whole filter.