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Consumer’s Guide to Showerhead Filters

Many people regard a long, hot shower as one of life’s unalloyed pleasures. The gentle liquid pelting…the soothing hot steam…the billowing cloud of toxic chlorine gas—whoa! Something’s wrong with this picture, but fortunately it can be made right with a relatively simple technical fix.

The fix is a filter for your showerhead. Shower filters have become much more popular in recent years as evidence continues to mount that the chlorine added as a disinfectant to public water systems is a health hazard, and that many people may be getting much more exposure to chlorine and its toxic byproducts by inhaling it in the shower than by drinking it in their tap water. Chlorine and other chemicals are evaporated from hot shower water and easily inhaled, not only in the close confines of the shower but also in the bathroom, where other members of your family can be exposed as well. The pores of your skin also open up from the steam and allow increased absorption of waterborne pollutants. One estimate is that you can be exposed to as much water pollution during a twenty-minute hot shower as by drinking two quarts of tap water per day.  

Is Chlorine a Hidden Menace in Your Shower?

Even if you can’t smell its pungent odor, chlorine may be a hidden menace in your shower, causing ailments ranging from headaches to neurotoxic reactions. In the digestive tract chlorine can upset the balance of intestinal flora and promote candida or other infections. Researchers have suggested that chlorine and its toxic byproducts may be responsible for an increased risk of heart disease, allergic reactions, and spontaneous abortions. Studies indicate that consumption of chlorinated water is linked to significantly increased rates of bladder, colon, and rectal cancer. One recent researcher has even noted that chlorine-related toxins may be proven in the future to be "the most important environmental carcinogens in terms of the number of attributable cancers per year."

In addition to its adverse effects on health, chlorine has unwanted topical and cosmetic actions on hair and skin. Anyone who has spent too much time in an overly chlorinated pool can attest to chlorine’s ability to irritate the eyes and aggravate mucous membranes in the nose and throat. Chlorine bonds with proteins in the hair, making it dry and brittle and causing color to be washed out. Chlorine strips skin of its natural oils, leaving it dry, itchy, and prematurely aged.

Chlorine has its place, as we’ll see, but that place should not be in your shower. 

Chlorine: A Versatile Germ-Killer

A greenish-yellow gaseous element that readily dissolves in water, chlorine may seem to be an unlikely health hazard—after all, water treatment officials routinely add it to the public drinking supply throughout the United States. They do this for a good reason: since it began to be used as a disinfectant almost two centuries ago, chlorine has probably saved hundreds of thousands of lives because of its ability to destroy harmful bacteria, viruses, and other pathogens.

Chlorine disinfection was recognized as a potential lifesaver as early as the 1820s by European physicians who were concerned about the extremely high rates of post-birth deaths in hospital maternity wards. Well before Pasteur’s work in the early 1860s convincingly established the germ theory for transmitting disease, a number of pioneering physicians had begun to use chlorine to disinfect hospital rooms. Some concerned physicians also had doctors wash their hands in a chlorine solution before they examined patients. Such practices dramatically reduced maternal mortality from puerperal fever, a highly contagious streptococcus infection of the uterus after birth, which was killing as many as one in six recently delivered mothers in some hospitals. In hindsight we know that many if not most of these deaths were from bacterial infections induced by "the examining finger"—doctors and medical students at the time routinely went directly from dissecting cadavers to probing the genitals of women.

Chlorine began to be used in U.S. water systems in the early 1900s because it killed the salmonella bacteria that were causing outbreaks of typhoid fever, and the vibrio bacteria responsible for cholera. Chlorine is now used in approximately 75 percent of public water systems in the U.S. to prevent waterborne diseases. It is added routinely in many areas to prevent bacterial growth in water mains. Water systems with leaky and aging pipes and other infrastructure are especially prone to contamination by microorganisms, such as from fecal matter from leaky septic systems. Water officials often add chlorine in higher amounts during the summer, when the risk of bacterial contamination of water increases. If a routine water test suggests a potential bacterial contamination, public water may be spiked with higher-than-average levels of chlorine, in some instances up to 8 parts per million (ppm).

Most people can smell residual chlorine at a concentration of about 3-4 ppm. If you’re not sure whether your drinking water is being treated with chlorine, check with your local water officials.

A Double-Edged Tool

Although chlorine has no doubt saved many lives by preventing deadly diseases, its toxicity toward microorganisms is a double-edged tool. Although relatively small amounts are used to disinfect water supplies, even low concentrations of chlorine are clearly detrimental to human and animal health. It is widely considered an air pollutant at a mere 1 ppm. Inhaling high levels, like 600 ppm, for 10 minutes can be fatal, a fact that militaries recognized back in World War One, when chlorine was used to make poisonous gas weapons. Chlorine is also toxic and irritating to the skin.

Chlorine is an effective bacteria-killer in part because it is so reactive. Free chlorine in water oxidizes and kills microorganisms, and it also readily combines with other chemicals, such as carbon, to form toxic compounds such as carbon tetrachloride. When organic matter such as leaves fall into a reservoir, they decay and release organic compounds into the water. As chlorine combines with these, it forms water pollutants known as trihalomethanes (THMs). These highly toxic chlorination byproducts include chloroform and trichloroethylene (TCE). If chlorine is present in water, in all likelihood the volatile chemicals chloroform and TCE are as well. 

Don’t Underestimate Shower Exposure

Until the mid-1980s, most studies that looked at adverse effects from waterborne contaminants considered people’s exposure through only one route: drinking. Research conducted since then, however, has demonstrated that this was a very one-dimensional approach to the issue. Trichloroethylene and chloroform in particular may be much more worrisome as water toxins that are inhaled or absorbed through the skin. Both TCE and chloroform are readily absorbed from the lungs into the blood. A number of recent studies have added to the weight of concern:

According to a 1999 study conducted by researchers at the Environmental and Occupational Health Sciences Institute in Piscataway, N.J., "Strong relationships were identified between the THM breath concentrations collected after a shower and both the THM water concentration and the THM exposure from a shower."

A 1998 study conducted in Taiwan compared the cancer risk at three major metropolitan areas with chloroform exposure during showering. The researchers considered exposure from all three major routes: ingestion, inhalation, and skin absorption. They concluded that a ten-minute shower would result in chloroform exposure with a 3:4:3 ratio (ingestion, inhalation, skin absorption); for a 20-minute shower the ratio was 1:7:2. In other words, those who were taking 20-minute showers were getting 90 percent of their exposure to chloroform from the shower. The researchers also determined that the cancer risk was almost thirteen times as high for a person who took a 20-minute shower in the area with the highest chloroform concentrations in the water compared to the risk for a person who took a ten-minute shower in the area with the lowest concentration.

According to the authors of a 1996 study, "The volatilization of volatile organic chemicals during domestic water usage can result in significant indoor air concentrations, and the subsequent inhalation of these contaminants is an important route of exposure….The simulated daily exposure is well described by a simplified equation that is a function of the amount of time the individual spends in the shower, the bath, and the bathroom; the total water usage in the home; and the fraction of time the individual is at home."

The authors of another 1996 study set up an experimental shower to measure the release of toxins. At 104 degrees F., a common shower temperature, volatilization was found to be approximately 80 percent for TCE and 60 percent for chloroform. According to the researchers, "The temperature of the water typically had a dominant effect on the total release of each of the three chemicals from the shower water to the air."

The National Academy of Sciences estimated in 1986 that up to 1,000 Americans die each year from cancers resulting from drinking water; but the figure may be many times higher when you consider people’s exposure to these chemicals from inhaling them while taking showers. 

New Shower Filter Technology Limits Chlorine

Chlorine’s adverse health effects has caused the administrators of public water systems, and the owners of private and public swimming pools, to explore alternative, less toxic methods of germ control. New technologies such as the use of ozone may eventually replace chlorine, but in the meantime consumers can rely on water filters. Whole-house systems can remove chlorine in shower water, as well as various other contaminants, but the simplest and most cost-effective solution for many people is to install a filter for the showerhead.

In recent years a new type of showerhead filter, dubbed KDF, has become available. The filter medium is made from a copper zinc alloy, which works by attracting chloride ions and converting them to zinc chloride. Effective showerhead filters can remove chlorine to less than 0.1 ppm and reduce dirt, rust, and bad odors, leaving your shower water looking and smelling fresh and clean. High-output showerhead filters are available with replaceable and reversible (that is, able to operate in either direction) filter cartridges. (Periodic reversing of the filter ensures balanced filtration and back-flushes the cartridge as it is filtering.)

Adding a filter to your showerhead can make that long, hot shower the unalloyed pleasure it ought to be. 

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Girodino, N.J, and J.B. Andelman, "Characterization of the emission of trichloroethylene, chloroform, and 1,2-dibromo-3-chloropropane in a full-size, experimental shower," J Expo Anal Environ Epidemiol, 6(4):413-23, 1996 Oct-Dec

Kuo, H.W., et al., "Estimates of cancer risk from chloroform exposure during showering in Taiwan," Sci Total Environ, 218(1):1-7, 1998 Jul 11

Weisel, C.P., et al., "Exposure estimates to disinfection by-products of chlorinated drinking water," Environ Health Perspect, 107(2):103-10, 1999 Feb

Wilkes, C.R., et al., "Modeling the effects of water usage and co-behavior on inhalation exposures to contaminants volatilized from household water," J Expo Anal Environ Epidemiol, 6(4):393-412, 1996 Oct-Dec