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The many considerations in shower filter design
Shower filter dechlorination requires its own unique design approach to meet various health requirements.In less than 10 years, shower filters have grown from a non-industry to a significant niche market. Consumers, at first only concerned with the quality of their drinking water, are now more aware of the importance of removing chlorine, one of nature's most toxic elements, from their shower water, too.
Yet, the similarity between drinking water filters and shower filters stops there. Shower filter dechlorination requires its own unique design approach to meet the elevated temperatures, high flow rates and size limitations of shower installations, all while providing users with an enjoyable shower experience. With more manufacturers jumping into the market, a better understanding of how filtration media, filter body size, flow rates, and shower head quality factor into the design equation can guide you toward the best product selection.
The most important contribution shower filters make toward a healthier lifestyle is reducing the amount of free chlorine that comes into direct contact with your skin. Outrageous claims such as shower filters reducing the risk of heart attack and cancer are just that, outrageous. Any manufacturer touting unsubstantiated claims should be viewed with suspicion.
The primary benefit is the removal of free chlorine. Chlorine is an inorganic substance that chemically bonds to the protein in your hair and skin, destroying the natural ecological balance of the skin. A quality dechlorinating shower filter will consistently remove 90 percent of free chlorine, resulting in softer, more manageable hair and healthier, younger-looking skin. For chlorine-sensitive people, particularly small children, the elderly and sufferers of asthma or emphysema, chlorine removal also is a safeguard against negative allergic reactions.
In developing a dechlorinating shower filter, designers are basically limited to two media types acceptable for potable water use: granular activated carbon (GAC) and atomized brass (KDF). Other media have been tried-the most notable being calcium sulfate-but were not deemed acceptable for direct human contact.
GAC is an effective dechlorinating medium. Many early manufacturers thought its properties were directly transferrable 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 degrees F. At these elevated temperatures, some of the contaminants adsorbed by the carbon can slough off and re-enter the water stream.
GAC also is light in weight. Therefore, it requires a much larger housing to achieve the same density as other filter media. For example, 16 ounces of KDF can be housed in a filter body that is 3.2 ounces in weight and only a few inches long. For GAC to achieve the same level of performance, you would need enough media to fill a bucket. GAC is also highly adsorbent-like a cellulose sponge-and becomes saturated in hundreds of gallons versus thousands of gallons with KDF, requiring more frequent replacement.
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, despite some manufacturers' claims. However, it is extremely effective at free chlorine removal. KDF is also bacteriostatic and tends to reduce or eliminate fungus and mildew build-up in the shower.
KDF is composed of 50 percent copper and 50 percent 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 that re-establishes the original electrolytic environment that created the free chlorine. The chlorine is able to recombine with a metal ion, normally zinc, to form a soluble zinc chloride which washes out of the filter and is harmless to humans.
KDF not only offers dechlorination capabilities, but it lasts longer than carbon media. In general, a KDF shower filter will last one and-a-half years or more for a family of three. 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.
Because buyers are more familiar with the "gallonage" terminology, many KDF shower filter manufacturers list gallonage as a lifespan rating. However, this should be viewed as a warranty figure rather than a true representation of the actual life of the product.
If most of today's shower filter manufacturers use KDF, what's the difference from one filter to the next? The design and manufacture. There are several considerations when using KDF that need to be factored into the final shower filter design. One of the primary issues is contact time-the amount of time the media is in contact with the water before it exits the shower head. This determines the amount of media required and the most efficient housing size. The filter designer also should know how to manage the flow rate within the housing and through the shower head so the media has sufficient contact time to treat the water. The longer the water is in the presence of the media, the better the media performs. For optimum results, the flow rate should be no more than two gallons per minute (gpm).
The type of shower head sold with the filter is also an important factor. The shower head should provide the desired amount of water reduction, while giving the user an acceptable shower delivery. Inexpensive shower heads are often "water guzzlers" and may deliver water in excess of 2.25 gpm, exceeding federal regulations. To bring these heads into compliance, some manufacturers restrict the flow (much in the way you restrict flow in a garden hose by crimping the hose) to achieve a lower flow rate. This should not be an acceptable alternative to good design. Restricting flow in this manner can significantly compromise media contact time and, more importantly, shower delivery.
The best flow results are achieved with high quality, all-metal, flow reduction shower heads. Because shower delivery plays such an important-but often overlooked-role in the filtration process as well as the user's enjoyment of the shower, look for manufacturers who use name brand shower heads with guaranteed specifications.
You also should expect your manufacturer to offer a comprehensive line of shower filters to suit a range of needs. For example, KDF media is available in granular, filament or "fines" form. Your manufacturer should be able to guide you toward which type is best for a variety of low, medium and high pressure applications, and for domestic and international markets.
As the market heats up through growing public acceptance of the benefits of shower water dechlorination, expect to see improvements in media and the shower device itself. Enhancements to the feel of the water and improved soap and shampoo lathering will become more important, too, as the novelty of shower filtration wears off and the quality of the shower delivery becomes a bigger factor. Replacement cartridge filter units are also on the upswing. When considering a cartridge-type filter, be sure your manufacturer is knowledgeable in sizing the cartridge appropriately so that media effectiveness isn't compromised.
As the industry grows and consumers become more discerning, it will become more critical for distributors to select manufacturers who understand the technology, have broad product lines for import and export markets and who can assure them of quality products that consistently meet consumer expectations.