| Filter/Filtration Types | Blocks | Does Not Block |
| Carbon/Activated Carbon Two types:
i. Carbon Block ( higher effectiveness, more surface area) ii. Granulated Activated Carbon (less effective, less surface area) |
Effectiveness greatly depends on the quality of the carbon. Some just remove chlorine and improve taste and odor. 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. |
| Ceramic | Blocks solid contaminants such as cysts and sediments. | Do not remove chemical contaminants. |
| Deionization | Removes mineral salts and other electrically charged molecules (ions) from water. | Cannot remove non-ionic contaminants (including trihalomethanes and other common volatile organic compounds) or microorganisms. |
| Distillation | Removes minerals, many bacteria and viruses, and chemicals that have a higher boiling point than water. | Cannot remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). |
| Ion Exchange | Replaces undesirable ions with others that are more desirable. The common application is water softening, which replaces calcium and magnesium with sodium. | Cannot remove non-ionic contaminants (including trihalomethanes and other common volatile organic compounds) or microorganisms. |
| Mechanical Filters | Removes contaminants such as cysts and sediments. | Cannot remove any chemical contaminants. |
| Ozone | Kills bacteria and other microorganisms. | Not effective in removing chemical contaminants. |
| Reverse Osmosis (Filters use 3-to-20 times more water than they produce) | Can remove many contaminants not removed by activated carbon, including arsenic, fluoride, hexavalent chromium, nitrates, and perchlorate. Quality can vary tremendously in both the membrane system and the carbon filter typically used with it. | Does not remove chlorine, trihalomethanes or volatile organic chemicals (VOCs).Systems include an activated carbon component than can remove these other contaminants. |
| UV (ultraviolet) | Ultraviolet light is used to kill bacteria and other microorganisms. | Cannot remove chemical contaminants. |
| Water Softeners(Treated water typically has high sodium content.) | Uses an ion exchange process to lower levels of calcium and magnesium (which can build up in plumbing and fixtures) as well as barium and certain forms of radium. | Do not remove most other contaminants |