Sediment Filters: Solid particles are strained out of the water. Fiber sediment filters contain cellulose, rayon or some other material spun into a mesh with small pores. Suspended sediment (or turbidity) is removed as water pressure forces water through tightly wrapped fibers. These filters come in a variety of sizes and meshes from fine to coarse, with the lower micron rating being the finer. Depth type sediment filters are constructed typically from melt blown polypropylene, and trap sediment in an ever-constricting matrix as the water flows through the filter structure. The finer the filter, the more particles are trapped and the more often the filter must be changed. Sediment filters will not remove contaminants that are dissolved in the water, like lead, mercury, trihalomethanes or other organic compounds.

Ceramic sediment filters are much like fiber filters using the process where water is forced through the pores of a ceramic filtration media. This type of filter can reduce some asbestos fibers, cysts (if the pores are one micron or smaller), some bacteria (with pore sizes in the - 1 micron range) and other particulate matter. Ceramic filters will not remove contaminants that are dissolved in the water, like lead, mercury, trihalomethanes or other organic compounds. These filters may be used as a back-end to an activated carbon filter to provide a more thorough removal of contaminants.

Activated carbon filters: particles of carbon that have been treated to increase their surface area and increase their ability to adsorb a wide range of contaminants. Coconut shell carbon and bituminous (coal) carbon are the most common sources of carbon in activated carbon filters. While bituminous carbon is the more cost effective type of carbon, coconut shell carbon is preferred in home applications due to the superior taste it imparts on the product water. The raw carbon source is slowly heated in the absence of air to produce a high carbon material. Passing oxidizing gases through the material at extremely high temperatures activates the carbon. The activation process produces the pores that result in such high adsorptive properties.

Activated carbon is particularly good at adsorbing organic compounds. You will find two basic kinds of carbon filters - Granular Activated (GAC) and Solid Block Activated. It is important to note - particularly when using counter-top carbon filtration systems - that hot water should NEVER be run through a carbon filter, because hot water will tend to release trapped contaminants into the water flow potentially making the water leaving the filter more contaminated than the water going in. The lone exception to this rule is carbon mixed with KDF 55.

Granular Activated (GAC): In this type of filter, water flows through a bed of activated carbon granules which trap some particulate matter and remove chlorine, organic contaminants, chemicals, and undesirable tastes and odors The main problems associated with GAC filters are: channeling, and dumping. Water flowing through the filter can "channel" around the carbon granules and avoid filtration. Pockets of contaminated water can form in a loose bed of carbon granules. With changes in water pressure and flow rates, these pockets can collapse, "dumping" the contaminated water through the filter. The GAC filters used in the Tap Master series, Value Line Chemical Fighter series, and the Tap Master Jr F2 water filters use spring loaded pressure disks to compress the granular activated carbon and prevent channeling and dumping. High quality GAC filters will expose each drop of water to more carbon surface area than in solid carbon block filters.

KDF Medium: KDF filter additive employs a matrix (generally small granules) of a zinc/copper alloy, which eliminates contaminants from water by utilizing electrochemical oxidation-reduction. Chemical properties of KDF include the ability to remove chlorine, kill algae and fungi, and control bacterial growth in the filter. KDF controls and inhibits microorganisms by setting up an electrolytic field and also by forming peroxide and hydroxyl radical by redox reactions. Types of KDF will also remove hydrogen sulfide, iron, lead, cadmium, aluminum, mercury, arsenic, and other inorganic compounds. Zinc and copper are the preferred metals used in the KDF alloy since both are relatively good reducing agents with respect to common inorganic contaminants (such as chlorine), and both can be tolerated in solution in moderate concentrations without adverse side effects. Zinc chloride is soluble, while cupric sulfide and ferric oxide are insoluble therefore, both copper sulfide and ferric oxide must be backwashed off the KDF granules so the insoluble contaminants will not inhibit the working efficiency of the KDF granules.

KDF is the only filter medium that removes contaminants from running hot water (unlike carbon filters where hot water can release trapped contaminants into the water stream). This makes them ideal for use in the shower. The filters change the chlorine some people are allergic to into a form (zinc chloride) that is much more easily tolerated. KDF filter media must be used in conjunction with other filtration technologies, such as GAC and/or reverse osmosis, in order to remove organic chemicals (pesticides, disinfection byproducts, MTBE, etc), or parasitic cysts (giardia and cryptosporidium).

Carbon Block: Activated carbon is the primary raw material in solid carbon block filters; but instead of carbon granules comprising the filtration medium, the carbon has been specially treated, compressed, and bonded to form a uniform matrix. The effective pore size can be very small, down to 1 micron. Carbon block filters provide a small pore size to physically trap particulates. In some cases bacteria that become trapped in the pores do not have enough room to multiply, eliminating the problem described above for GAC filters. By combining other specialized materials with carbon block, greater capacity ratings for certain contaminants like lead, mercury, etc can be achieved.

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