In developing a dechlorinating shower filter, designers are basically limited to two media types acceptable for potable water use: GAC (granular-activated carbon) and KDF (atomized brass). Other media have been tried, most notably calcium sulfate, but were not deemed acceptable for shower filter use.

GAC is an effective dechlorinating medium, and many early manufacturers thought its properties were directly transferable to shower filter applications. Not so. First, carbon is not recommended for hot water use. Unlike drinking water units which, on average, operate at ambient temperatures, shower filters are continuously exposed to temperatures ranging from body temperature to 105 F. At these elevated temperatures, some of the contaminants absorbed by carbon can slough off and reenter the water stream.

Since GAC is also light in weight, it requires a much larger housing to achieve the same density as other filter media. The density of KDF allows for a more efficient use of space. For example, 16 ounces of KDF can be housed in a filter body with only 12–13 cubic inches of internal capacity. For GAC to achieve the same level of performance, you would need enough media to fill a bucket or more! GAC is also highly absorbent—like a cellulose sponge—and becomes saturated with contaminants after only hundreds of gallons of use versus thousands of gallons with KDF, requiring more frequent replacement.

Rainshow'r Mfg. Co., Inc. was the first shower filter manufacturer to use KDF in their shower filter and today, non-carbon shower filters are the norm, and KDF the preferred media among shower filter designers. This non-organic filtration media does not remove organic contaminants. Contrary to the claims of other shower filter manufacturers, KDF Fluid Treatment, Inc. states that heavy metals such as lead, cadmium, arsenic, and mercury cannot be removed with the amount of KDF used in a short filter body at a high flow rate, as exist in a shower filter. However, it is extremely effective at free chlorine removal. KDF is also bacteriostatic (inhibits reproduction), and tends to reduce or eliminate fungus and mildew build up in the shower.

KDF is comprised of 50% copper and 50% zinc. It removes free chlorine by reversing the electrochemical process that originally separated the chlorine from sodium in a brine solution. Here's how it works: Copper and zinc are dissimilar metals. The tension between these metals generates between 900 and 1100 millivolts of electricity in an aqueous state (i.e., as water passes through the media). This is enough electricity to generate a galvanic charge, which reestablishes the original electrolytic environment that liberated the free chlorine. The chlorine is able to recombine with the most prevalent metal in the water, usually calcium, to form a soluble chloride, which washes out of the filter and is harmless to humans.

KDF not only offers superior dechlorination capabilities, it lasts much longer than carbon media does. Depending upon the filter model and the amount of KDF, a KDF shower filter should last seven to nine months. However, it should be noted that KDF's effectiveness is measured by its ability to generate the electrochemical action described earlier - not in gallonage. The cathode-anode relationship between copper and zinc (which generates the galvanic charge) is disrupted by particulate contaminants in the water. As a result, the less particulate matter in the water entering the filter, the longer the KDF media will generate adequate levels of electricity to effectively remove free chlorine. So, a KDF shower filter in Bangor, Maine, where the particulate contaminants in the water are low, will last a lot longer than one in Albuquerque, New Mexico.