If you have been considering purchasing a filter to convert your tap water into clean drinking water, be sure to compare home water purifiers before buying one. Each type uses a slightly different method of filtration, and each individual method of filtration eliminates different classes of contaminants. The best - but most expensive - home water purifiers use multiple methods of filtration, while less expensive home water purifiers use a single method and may do just fine for your purposes.

When you compare home water purifiers, start by looking at how they work: do they attach to your faucet or do you use them in a special pitcher? A few home water purifiers even attach to the main line of your home, but these are not common. In each case, you should consider how you need to use your home water filter: drinking only, or cooking as well? Do you want refrigerated water anyway? Do you need exceptionally easy-to-use filters? In some cases, you can even find home water purifiers that do special things, like add flavor to your water.

Compare home water purifiers by the method used in filtering your water. Start with the two most common: activated carbon filters and reverse osmosis filters. Other filter types are the KDF-55 or the greensand iron filter; a fifth, the ultraviolet filter, is used primarily in hospitals and industrial settings. For most home water filters, reverse osmosis and activated carbon are the most likely types of filter. Each filter type has a somewhat different action on water and generally removes different contaminants.

The most common is the activated carbon purification system. In this filter type, the extreme natural reactivity of carbon to most natural chemicals is the method used to eliminate contaminants in water. Because of the way water dissolves things, each contaminant has a slight negative charge, while activated carbon has a slight positive one. Positive carbon reacts with negative contaminants much the same way the different polarities of a magnet work, and impurities are attracted to and held by the carbon until most of the positive carbon charge is used up. This makes it a very effective purifier. The two primary types of carbon used in filters are the granular activated carbon (GAC) and powdered block carbon, with the powdered block being slightly more effective overall. Both types of activated carbon remove chlorine, radon, pesticides and other volatile organic compounds (VOCs), sediments, bad tastes, and a portion of hydrogen sulfide and some heavy metals.

While reverse osmosis purifiers are more involved to install, they also make much better purifiers, delivering water of bottled water grade. The osmotic barrier inside these purifiers is an ultrathin membrane that allows the passage of water, but not of contaminants, so that you wind up with pure water on one side and significantly more impure water on the other. Most reverse osmosis home purifiers consist of the purification system (with an activated carbon filter in addition to the osmotic filter) and a reservoir that delivers purified water directly to your tap. In addition to the contaminants removed by activated carbon, reverse osmosis purifiers remove bacteria, viruses, arsenic, chlorine, fluoride, nitrates, iron, and all heavy metals.

Base your choice of home water purifiers on a consideration of how the purifiers work, what they cost to install, how you plan to use your water, and what is removed during the purification process. You may find that, while the osmotic system removes more contaminants, the cheaper activated carbon filters work just fine for your needs.