The Basics of Common Water Filter Technologies
Carbon/Activated Carbon: Activated carbon chemically bonds with and removes some contaminants in water filtered through it. Carbon filters vary greatly in effectiveness: Some just remove chlorine and improve taste and odor, while others remove a wide range of contaminants including asbestos, lead, mercury and volatile organic compounds (VOCs). However, activated carbon cannot effectively remove common “inorganic” pollutants such as arsenic, fluoride, hexavalent chromium, nitrate and perchlorate. Generally, carbon filters come in two forms, carbon block and granulated activated carbon.
Carbon Block: Carbon block filters contain pulverized activated carbon that is shaped into blocks under high pressure. They are typically more effective than granulated activated carbon filters because they have more surface area. Their effectiveness depends in part on how quickly water flows through.
Granulated Activated Carbon: These filters contain fine grains of activated carbon. They are typically less effective than carbon block filters because they have a smaller surface area of activated carbon. Their effectiveness also depends on how quickly water flows through.
Ceramic: Ceramic filters have very small holes throughout the material that block solid contaminants such as cysts and sediments. They do not remove chemical contaminants.
Deionization: These filters use an ion exchange process that removes mineral salts and other electrically charged molecules (ions) from water. The process cannot remove non-ionic contaminants (including trihalomethanes and other common volatile organic compounds) or microorganisms.
Distillation: This technology heats water enough to vaporize it and then condenses the steam back into water. The process removes minerals, many bacteria and viruses and chemicals that have a higher boiling point than water. It cannot remove chlorine, trihalomethanes or volatile organic chemicals (VOCs).
Mechanical Filters: Like ceramic filters, these filters are riddled with small holes that remove contaminants such as cysts and sediments. They are often used in conjunction with other kinds of technologies, but sometimes are used alone. They cannot remove chemical contaminants.
Ozone: Ozone kills bacteria and other microorganisms and is often used in conjunction with other filtering technologies. It is not effective in removing chemical contaminants.
Reverse Osmosis: This process pushes water through a semi-permeable membrane that blocks particles larger than water molecules. Reverse osmosis can remove many contaminants not removed by activated carbon, including arsenic, fluoride, hexavalent chromium, nitrates and perchlorate. However, reverse osmosis does not remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). Many reverse osmosis systems include an activated carbon component that can remove these other contaminants. Quality can vary tremendously in both the membrane system and the carbon filter typically used with it. [Note - many reverse osmosis systems use 3-to-20 times more water than they produce. However, Liquos uses a permeate pump on all systems allowing the recovery rate to be stabilized at three gallons waste water for each gallon of filtered water produced.]
UV (ultraviolet): These systems use ultraviolet light to kill bacteria and other microorganisms. They cannot remove chemical contaminants.
Water Softeners (ion exchange): These devices typically use an ion exchange process to lower levels of calcium and magnesium (which can build up in plumbing and fixtures) as well barium and certain forms of radium. They do not remove most other contaminants. Since water softeners usually replace calcium and magnesium with sodium, treated water typically has high sodium content. Some people may be advised by their physicians to avoid softened water. For the same reason, it is also not recommended for watering plants and gardens.
Source: Environmental Working Group, 2013
http://www.ewg.org/report/ewgs-water-filter-buying-guide/filter-technology