Compare Water Filter Technologies

Carbon / KDF / Distillation / RO / Bottled Water

Carbon Filters

Carbon has a long history of being used to absorb impurities and is perhaps the most powerful absorbent known to man. One pound of carbon contains a surface area of roughly 125 acres and can absorb literally thousands of different chemicals. Activated carbon is carbon which has a slight electro-positive charge added to it, making it even more attractive to chemicals and impurities. As the water passes over the positively charged carbon surface, the negative ions of the contaminants are drawn to the surface of the carbon granules. Activated carbon filters are usually rated by the size of the particles they are able to remove, measured in microns, and generally range from 50 microns (least effective) down to 0.5 microns (most effective).

Carbon filters are NOT generally successful at removing dissolved inorganic contaminants or metals such as minerals/salts (hardness or scale-causing contaminants), antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, copper, fluoride, mercury, nickel, nitrates/nitrites, selenium, sulfate, thallium and certain radio nuclides. Removing these contaminants requires either a reverse osmosis water filter system or a distiller (some can also be removed by KDF-55 or manganese greensand).

Carbon filters comes in many options and the percentage removal of particulates, chlorine, cysts, etc. depends on the porosity of filter and additional "add ons."  Carbon does not kill bacteria or viruses (microbials), and, in fact, can become a breeding ground for microbials

Simplistic, single technology filters are not a true solution to water problems.The most common carbon types used in water filtration are bituminous, wood, and coconut shell carbons. While the coconut shell carbon typically costs 20% more, it is generally regarded as the best of the three.

GAC (Granular Activated Carbon) Verses Carbon Block

Activated carbon filters used for home water treatment typically contain either granular activated carbon (GAC) or powdered block carbon. Although both are effective, carbon block filters generally have a higher contaminant removal ratio. The two most important factors affecting the efficiency of activated carbon filtration are the amount of carbon in the unit and the amount of time the contaminant spends in contact with it. The more carbon the better. Similarly, the lower the flow rate of the water, the more time that contaminants will be in contact with the carbon, and the more absorption that will take place. Particle size also affects removal rates.

Any granular activated carbon filter has three inherent problems.

1. It can provide a base for the growth of bacteria. When the carbon is fresh, virtually all organic impurities (not organic chemicals) and even some bacteria are removed. Accumulated impurities, though, can become food for bacteria, enabling them to multiply within the filter.

2. Chemical recontamination of granular activated carbon filters can occur in a similar way. If the filter is used beyond the point at which it becomes saturated with the impurities it has absorbed, the trapped impurities can release from the surface and re-contaminate the water, with even higher concentrations of impurities than in the untreated water. This saturation point is impossible to predict.

3. Granular carbon filters are susceptible to channeling. Because the carbon grains are held (relatively) loosely in a bed, open paths can result from the buildup of impurities in the filter and rapid water movement under pressure through the unit. In this situation, contact time between the carbon and the water is reduced, and filtration is less effective.

Solid Block Carbon is created by compressing very fine pulverized activated carbon with a binding medium and fusing them into a solid block. The intricate maze developed within the block ensures complete contact with organic impurities and, therefore, effective removal. Solid block carbon filters avoid the problems just discussed with granular carbon filters.

Block filters can be fabricated to have such a fine porous structure that they filter out coliform and associated disease bacteria, pathogenic cysts such as giardia, and lighter-weight VOCs. Block filters eliminate the problem of channeling. Also, they are so dense that they do not allow the growth of bacteria within the filter.

Coconut Shell Carbon

Coconut shell carbon has a superior level of hardness that makes them cleaner than most other carbons and gives them longer life expectancy. This, combined with their high activity level, makes them well suited for use in any kind of carbon-based filtration system

Acid Washed Granular Coconut Shell Activated Carbon comes from coconut shell that has undergone a steam activation process to create its activated carbon form. During activation, it creates millions of pores at the surface of the carbon thus increasing the total surface area. Coconut shell carbon is rated by the iondine level which mesure how well it absorbs contaminats, ranging from a low of 400 to a high of 1200. (NOTE: CuZn Water Filters use acid washed coconut shell activated carbon rated at 1100)

Activated carbon pores can be divided into three general micron sizes: 1) Micro-pores (diameter in the range of less than 2 nm), 2) Meso-pores (diameter in the range of 2 - 25 nm), and 3) Macro-pores (diameter in the range of above 25 nm). Coconut shell carbon has mainly micro-pores to meso-pores, and due to its unique distribution of pores diameter, coconut shell activated carbon are very popular in the gas phase purification and potable water purification industries.

KDF 55 and 85 Filters

The KDF55 redox media is a patented, high purity alloy of copper and zinc. It eliminates contaminants from water by utilizing the principle of electrochemical oxidation-reduction, known as redox potential. Redox is simply the principle of opposites at work. Some substances are positively charged and are attracted to the negative charge of the zinc. Others are negatively charged and attracted to the positive charge of the copper. KDF55 media uses the redox principle in the presence of dissolved oxygen to effectively remove chlorine, chlorinated hydrocarbons, hydrogen sulfide, iron, and metals like lead, arsenic, aluminum, mercury, and cadmium from water. As water containing dissolved substances enters a bed of high purity copper-zinc granules, copper becomes a cathode and zinc an anode. The tiny space between each granule becomes an electrolytic cell, with the water and its contents acting as the electrolyte.

KDF 55 Medium was designed specifically for removing or reducing chlorine and water-soluble heavy metals. KDF 85 Medium removes or reduces chloramines, iron and hydrogen sulfide from municipal or other water supplies. KDF 55 and KDF 85 Process Media can remove up to 99% of water-soluble lead, mercury, nickel, chromium, and other dissolved metals. All KDF Process Media forms are effective in controlling the buildup of bacteria, algae, fungi and scale, even in hot water, making them ideal for use in GAC beds, ion exchange resins, carbon block filters and inline carbon filters.

NOTE: CuZn Water's patented KDF copper-zinc disks have several advantages over granular KDF. Their disks eliminate the need for backwashing, conserve water, reduce compaction, eliminate the need for cartridges and plastic waste and are even recycleable. The disks are easier to use, maintain and refill than cartridge systems, plus they offer greater surface area for better performance. See How CuZn Water Filtration Works


Energy input required for distillation involves a higher operating expense than other methods and the maintenance factor is extremely high. Impurities remain in the boiling chamber and are either automatically or manually flushed out depending on the system. Air cooled distillers produce one gallon of distilled water for every gallon of tap water. Water cooled units produce one gallon of water from eight to 15 gallons of tap water.

The costs of producing a gallon of distilled water ranges anywhere from 20 - 40 cents per gallon because they use about 3 kilowatt hours of electricity for one gallon. Distillation also produces "flat" tasting water.

Reverse Osmosis (RO)

Water is passed through a pre-filter (5 microns) to remove particulates and sediment, then applied under pressure to a semipermeable membrane. The membrane will remove up to 98% of TDS including bacteria and cysts, but allows small molecules of water and soluble chemicals to pass. The impurities collected on the membrane must be flushed from the system. Water then goes through an absorption filter to improve taste, odor and color and to reduce chemical contaminants. A residential system can produce anywhere from one to 20 gallons per day. Water is stored in a sealed container. A final filter is used to reduce tastes and odors which can be introduced by the storage unit.

Other facts about reverse osmosis systems:

  • American Water Works warns that RO systems do not remove tiny microorganisms without the use of UV light.
  • Most RO systems waste 50 - 75% of the water it processes. "Waste water" is the drawback: 2 - 4 gallons or more of water is wasted for every 1 gallon of product water.
  • Membranes only last for 5000 -10000 gallons.
  • Systems are large and bulky.
  • Water tastes flat.

Bottled Water

Source and purity are questionable. No guarantee water is any better than tap water. Can cost more than gasoline. The ideal is to fill your own bottles from filtered water. Also, when traveling, try a filtered water bottle.

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