Granular Activated Carbon Filters
“Activated” carbon refers to charcoal that has been exposed to high temperatures and steam in the absence of oxygen. Vegetable charcoal, often derived from coconut hulls, is the most common material used. The result of activation is a honeycomb-like superstructure that is filled with millions of tiny tunnels. This granular activated carbon (GAC) contains a microscopic labyrinth with an enormous surface area on which carbon molecules can cling. This is the reason for carbon's fantastic adsorptive capacity. One pound of granular activated carbon provides a surface area equivalent to 125 acres!
Simple charcoal filters for treating tap water are widely available in department, kitchen, and housewares stores and even supermarkets. They range in price from $20 to $60. More sophisticated charcoal filters can cost in the $200 to $400 range. The wide span of prices reflects major differences in quantity of charcoal, design, durability, convenience, and most importantly, scope of pollutants treated. But the real cost of a filter is found in the expense of its replacement cartridges. These are like razor blades to the razor. Before you buy, check the cost of replacements. You will be replacing the filter cartridges as little as once per year to as much as twelve times per year and it will be your primary expense. If a cartridge costs $75 and lasts for 500 gallons, for example, your water cost is 15 cents per gallon.
On the low end of charcoal filters is the common carafe filter. Basically, this is a water pitcher that filters like a coffee maker. Tap water is poured into the top, runs down through a small filter, and the filtered water lands at the bottom. It significantly reduces chlorine, gases, odors, and tastes. The carafe is inexpensive (approximately $20), portable, and easy to use. But, the filters need to be changed one to two times per month to avoid bacterial growth. Based on the cost of a typical replacement filter, this amounts to approximately 30 cents per gallon. This frequent changing is also bothersome for most folks who slack off on their filter-changing responsibilities. This laziness can result in water that is more contaminated than what comes out of the tap!
Faucet mounted canisters are another inexpensive ($25-$60) type of charcoal filter. They contain small amounts of charcoal. In some brands, tap water may drill a hole through the center of the canister because the charcoal is loosely packed. This makes for a speedy flow rate but minimal contact time with the charcoal. These filters also need to be changed frequently to avoid bacterial growth. Their charcoal can also be damaged by the unintentional usage of hot water. High end faucet mounted filters may include micron strainers to effectively remove cysts such as giardia and cryptosporidium. Some even have bypasses for hot water and monitors to remind you to change the filter. They can remove chlorine, gases, odors, tastes and reduce volatile organic compounds (VOCs), trihalomethanes (THMs), and pesticides.
All simple charcoal filters should be replaced frequently. Dark, moist charcoal turns out to be an ideal breeding ground for bacteria. After a few weeks, the bacterial population is large enough to leak out of the filter. Old filters can only hold so much. Some units actually start to unload their pollutants when they reach their saturation point, recontaminating the water.
A better carbon filter is the tall column model. These range from 6 inches to 2 feet and contain large quantities of densely packed charcoal. The water moves down the long tube, getting cleaner and cleaner as it journeys to the bottom. These units can be installed at the point where the water enters the house, or under a sink, or on the countertop. Countertop units connect to the faucet via a tube and often have a spigot at their top to dispense the filtered water. They range in price from $50-$200 and effectively remove chlorine, gases, odors, tastes and reduce an even greater percentage of volatile organic compounds (VOCs), THMs, and pesticides.
Carbon Block Filters
So far the carbon filters we have discussed do an excellent job of reducing two categories of pollutants: aesthetic impurities such as those that affect water taste, odor, and turbidity; and health impurities such as pesticides, VOCs, THMs, gases, and many other organic compounds. Carbon block filters begin to work in a third area, that of inorganic, metals, and bacteria.
Carbon block filters contain great volumes of charcoal compressed into super-dense blocks. Most also include layers of other media that filter the water before and after the charcoal. The technology behind carbon blocks can get very sophisticated. Some use different activating processes that create new geometric lattices that increase the adsorptive area. They range in price from $200-$400. They effectively remove chlorine, toxic gases, odors, tastes, VOCs, THMs, pesticides, organic compounds, heavy metals such as lead, and bacteria and cysts such as E. coli, protozoa, giardia, and cryptosporidium.
These units are often mounted under the sink where they connect directly to the cold water pipe. On the sink top, all you see is a fountain spigot. Countertop models use the same filter cartridge but have a housing that attaches to the faucet end via a double tube. The faucet works normally for washing dishes and is easily diverted to the cartridge by turning a valve. Water travels through the filter in one tube and returns to the faucet via the second tube. The countertop models install easily by adding a diverter valve on the faucet tip. The under sink models require tapping into the cold water line and possibly drilling a hole for the new filter spigot, which could require a plumber. Both models last from 400 to 1,000 gallons which means replacing your filter one to three times per year.
When shopping for this kind of filter, consider flow rate. Some filters are so densely packed, it can get rather tedious waiting for a glass of water. However, this is preferred to the kind that “gushes” forth. Filters with slow flow rates of less than one half gallon per minute, generally provide good quality water by increasing the contact time of the water and charcoal. Flow rate also depends, of course, on your water pressure.
Charcoal filters are most effective early in their life and decrease their efficiency as the carbon's available surface area is filled up. Thus, if you have very dirty water with lots of large particle matter, it will make sense to use a pre-filter so that the adsorptive capacity of the carbon is not wasted on fibers, rust, dirt, etc. In better models, you will know when to change the filter because they have monitors that signal you by checking for decreasing flow rate.
Pros and Cons of Charcoal Filters
Bacteria is probably the greatest problem with basic charcoal filters because they can actually promote the propagation of bacteria, yeasts, molds, cysts, and other micro-organisms. Microorganisms love the dark, wet environment of a filter. The chlorine in your tap cannot get rid of all bacteria; it only keeps their counts low. Once your filter removes the chlorine, the bacteria multiply and feed off the trapped organic pollutants in it. This is a major disadvantage of charcoal filters. If you do not change the filter, you run the risk of breeding more bacteria than was in the original water!
The big question is then, how do you know when to change the filter? Most manufacturers will recommend a change period. But there are other variables such as your rate of usage or the age of your plumbing. Bacteria may build up to harmful levels in as little as 2-3 weeks. But how would you know? After all, bacteria don't come out and whistle!
What to Look for When Buying a Charcoal Filter Large amounts of densely packed charcoal Long filter life, preferably 400-1000 gallons Pre-filter to prolong the main filter's life Maximum contact time and reasonable flow rate Countertop unit connects directly to the faucet Under the sink unit saves space and is out of sight Hard side walls to maintain the integrity of the solid carbon block and prevent breakdown or contaminant feedback.
Pros & Cons of Charcoal Filtration
Advantages
• Best method for extracting toxic gases, odors, and tastes
• Best method for extracting all organic, hydrocarbon based pollutants such as pesticides, chlorine, THMs, and PCBs Most economical filtration method
• Some models have ability to reduce heavy metals such as lead, cadmium, and chromium. Some carbon block models can prevent entry of bacteria and pathogens such as giardia and E. coli.
Disadvantages
• Does not remove inorganic mineral salts such as sodium, fluoride, and nitrates
• Has little affect on soluble minerals, or asbestos fibers
• Provides a breeding ground for bacteria Has a limited life
• Difficult to determine when filter's effectiveness is used up
• Destroyed by hot water
• Carbon in some filters can break down and return contaminants to the drinking water
How do you know when to change your filter? Look for: a change in taste, odor, or color; a reduction in the flow rate; or the appearance of cloudiness or small particles. More sophisticated charcoal filters include monitors that signal you when they register a slower flow rate, indicating an aging filter, and others contain micro-strainers that prevent bacteria from exiting or entering the unit.
Another problem for charcoal is stagnation. If you use a filter for one week, and go on vacation the second week, you will likely return to a house with a million guests - bacteria! Manufacturers generally do not warn you about bacteria, for fear of scaring their audience. Nor would it be good business to suggest that you change your filters every couple of weeks. Others neglect to tell you not to use hot water. The adsorptive properties of charcoal are damaged by hot water and worse, it may liberate the contaminants held within. Submicron-Straining Carbon Purifiers
Some high-end carbon block filters are designed with submicron-strainers that wrap around the carbon core and prevent bacteria from either entering or leaving the filter cartridge. These units physically strain out ninety-nine percent of bacteria. Bacteria are generally larger than one micron in size, but micro-straining carbon filters can strain down to half that size, 0.5 microns, or better. To give you an idea of how small this is, a human hair is 100 microns thick and a red blood cell is 0.9 microns! This effectively eliminates cysts like cryptosporidium and giardia, pathogenic bacteria such as E. coli, salmonella, fungi, yeasts, and parasites, as well as tiny asbestos fibers that pass through ordinary carbon filters.
Bacteria are either prevented from entering the media or are trapped and never make it out. The technology for this kind of superfine straining was developed for the Gemini Space Program so astronauts could purify their own water in space. Micro-straining carbon block filters, however, do not remove viruses. Viruses are between 20 and 100 times smaller than bacteria. Nor do they eliminate inorganic chemicals, salts, or ions like fluoride, nitrates, and sodium. Only distillation and reverse osmosis treatment can reduce these.
Some of these carbon block strainers enhance their filtration with other technologies such as electrostatically charged layers. This could be a blend of cotton or cellulose that has been given a positive molecular charge. Since most colloidal pollutants, bacteria, and inorganic compounds exhibit a negative charge in solution, this filter layer absorbs the charged particles by electro-kinetic attraction. The effect is similar to the way lint is attracted to wool. This provides reduction of some contaminants that are not picked by micro-straining. The components of these purifiers are insoluble and chemically inactive themselves. They work by exerting a catalytic effect, inducing molecular changes in many chemicals contained within the water. It is in this manner that some of these devices can even extract a small percentage of negatively charged fluoride ions and even some dissolved minerals.
All these devices have their limits and their capacity to reduce contaminants deteriorates over time. Advertising claims about endurance can be misleading. Everyone's water is different and different conditions affect the life and performance of your filter. A conscientious manufacturer should test his unit at the maximum age limit of the device. In any event, it behooves you, as a lay person, to change your filter regularly and at the first suspicion of deterioration. One marker is a change in odor and taste. Although the filter may still be effective for other contaminants, these two changes are easy to detect and are indications of an aging filter. As an alternative, simply mark your calendar with filter-change dates and stick to it.
Pros and Cons of Micro-Straining Carbon Filters
The major advantage of a good micro-straining carbon filter is convenience, plus the elimination of bacteria. They provide water on demand, use no electricity, have easy maintenance, and easy installation. They waste no water, and effectively remove a wide range of pollutants including submicron size microorganisms. With all these features and affordable prices, they make a superb choice for many homes. You turn the knob and you get water. Isn't that the way it should be?
Disadvantages: hard carbon block micro-strainers still cannot remove inorganic chemicals such as fluoride, nitrates, sulfates, sodium, inorganic minerals, and any below submicron size organisms such as viruses.
Ceramic Filters
Ceramic filters are made out of clay or volcanic sand or magnetite stone. They are actually old technology. Henry Doulton developed the first ceramic water filters in the mid 19th century to provide safe water during a cholera epidemic in London. Doulton filters still exist today and deal with a wide range of contamination problems. They have two main advantages: Long filter life and the ability to extract inorganic chemicals and bacteria. Filter life of these units are all 1,000 + gallons. When they become clogged with particulates, just take them out and scrub them with a brush under cold water. Ceramic filters can efficiently purge inorganic chemicals, such as fluoride and nitrates, along with heavy metals, and bacteria. They can also control cysts such as cryptosporidium because the ultra fine ceramic screens down to 0.8 microns. Models are usually designed to work with charcoal to enhance their range of effectiveness to include parasites, lead, chlorine, dirt, turbidity, bad taste, and odor. Prices range from $200-$400.
KDF and Shower Filters
While the purity of our drinking water is of primary importance, contaminants and chlorine byproducts also enter our bodies through the skin via the water in which we bathe. Also, our lungs absorb toxic fumes from the gaseous chlorine byproducts that are released in a steamy shower. A report in Science News estimated we inhale enough pollutants in a ten minute shower to equal drinking a gallon of polluted water. Chlorine in shower water can strip protein from our hair and skin causing dry, irritated eyes, itchy skin, and dandruff. Hair can become dull and carry a chlorine smell. This is why people wear swimming caps. Filtering shower water also helps control bacteria and fight bathroom mold and mildew.
Shower filters attach directly to the showerhead or replace the showerhead itself. While charcoal is supremely effective for removing chlorine, the volume of water used in a shower is a thousand times more than for drinking. The frequency of refills that would be required makes it unsuitable. A new ion binding medium, known as KDF significantly reduces chlorine and heavy metals, and has a much longer life.
Advantages of KDF Filtration Eliminates Chlorine: Converts free chlorine to harmless chloride Reduces Heavy Metals: Redox principle changes lead ions in water to lead atoms which electroplate onto KDF surface Reduces Scale: Alters the nature of lime scale, changes crystalline structure so that scale turns into powder Kills Bacteria: KDF possesses inherent toxicity to bacteria; KDF is a patented copper-zinc alloy that filters by a process called reduction oxidation. Here is how it works. Since water is neutral, neither positively nor negatively charged, any particle that has a charge will be attracted to the filter. Pollutants actually bond to the zinc and copper. When a charged particle loses or gains electrons, it changes its composition. This changeover is known as reduction oxidation or redox for short.
Through this redox process, potentially harmful chemicals become harmless. Zinc reduces chlorine to soluble zinc chloride. Copper reacts with hydrogen sulfide to form cupric sulfide and scale changes from glass to powder. KDF is also effective in reducing lead, iron, arsenic, mercury, and hydrogen sulfide. After water has been in contact with KDF, oxygen-depleting bacteria cannot grow. And unlike charcoal, KDF functions in both hot and cold water conditions without any deterioration.
Most shower filters can also be backwashed to optimize their performance. Life of a good KDF filter is above 10,000 gallons, far superior to charcoal and about a years worth of showers and baths. KDF filters generally range in price from $50-$ 125. When buying a shower filter, check the ease of removal, installation, and reversal for backwashing.
Water Filters do their job.