Filtering your own tap water is the most economical and long-term solution to your water needs. Knowing which type of filer or apparatus to use is more challenging.
There are 3 common types of water filters:
1. Absorbent Filters
Absorbent filters, made of charcoal, are designed to pick up and hold contaminates as water passes over them.
Carbon filtering devices use carbon cartridges that have a porous surface. This allows the cartridge to absorb a variety of substances, including THMs, odors and disagreeable tastes. A filter's effectiveness depends on the amount of carbon in the unit and how long the water stays in the unit. The longer the water is in contact with the filter medium, the more time the carbon has to remove impurities. Those packed with a large volume of charcoal generally remove more organic material at the beginning of the cartridge life. Performance tends to decrease less rapidly over time than it does for those containers with a small amount of charcoal.
Granular Activated Carbon
In this type of filter, water flows through a bed of charcoal granules, which traps the particulate matter, adsorbs some chlorine, and removes tastes and odors. It is possible for the water to channel around the carbon granules, thus avoiding filtration. If the granules are not impregnated with silver nitrate (which is considered to be a poison), the granular beds may become breeding grounds for bacterial growth. This type of filter is primarily used for aesthetic treatment, since it can reduce chlorine and particulate matter as well as improve the taste and odor of the water. Granular Activated Carbon filters are not effective in reducing contaminants of health concern (cysts, VOCs, THM, endocrine disrupters, mercury, lead, or asbestos) because the water can channel around the carbon granules.
Carbon Block Filter
In this type of filter, carbon comes in a solid block. More carbon is used compare to the granular form, and the filtration effectiveness is better since water cannot pass in between the carbon granules. As the water passes through the block, chorine, pesticides, toxic chemicals and vital organic chemicals are removed. Carbon block filter is preferred compare to granular carbon. dirt, sediment, rust, algae, cryptosporidia, asbestos and particulate matter.
Specific advantages of carbon block filters are:
Chemical bonding: Activated carbon bonds to thousands of chemicals. In fact, carbon will bond to most chemicals known to man! When water is forced through the solid carbon block, it is forced to slow down and increase the contact time with the carbon, allowing the carbon bonding to take place to reduce certain chemical pollutants like toxics, pesticides, THM's, chlorine, bad tastes, odors, etc. Health-providing trace minerals like dissolved calcium and magnesium do not bond to carbon and are allowed to pass through, thereby retaining the health quality and good taste of the water. Heavy metals like lead are adsorbed (or collected) by the carbon.
Prevention of bacterial growth: Bacteria are strained out and remain on the outside of the carbon block. Therefore, because of the density and lack of oxygen and space inside the block, bacteria cannot breed in the medium and come out in the finished water.
Silver-Charcoal Filters (Bacteriostatic)
These are the same as activated charcoal filters. However, they use silver to inhibit the growth of bacteria while water sits in the filter. Silver ingested in certain doses can be poisonous to the human body. Therefore, it must be registered with the EPA as containing a poisonous substance.
2. Ion-Exchange Filters
These filters can be made of a variety of materials. They all have tiny holes designed to catch and eliminate contaminants as water passes through them. De-ionization or de-mineralization is accomplished with such filters, which are designed to remove heavy metals, including lead. To remove parasites, such as potentially deadly cryptosporidia, a microfilter must have a guaranteed pore size of one micron or smaller, according to the National Sanitation Foundation (NSF)
Fiber Filters
Fiber filters are comprised of spun celluose or rayon and are designed to take out turbidity (suspended sediment). The tightly wrapped fibers form a cylinder around a tubular opening. Line pressure forces water through the wrappings to the inner opening that leads to the faucet. The fibers trap silt. Filtered water passes to the opening that leads to the faucet.
Ceramic Filters
Ceramic filters use a process whereby water is forced through the pores of the ceramic filtration media, providing mechanical filtration only. This type of filter can reduce asbestos, cysts (if the pores are one micron or smaller), and particulate matter. Ceramic filters cannot reduce VOCs, endocrine disrupters, THM, mercury, or lead.
3. Reverse Osmosis Filtration System
Unlike other types of devices that reduce impurities in the water, reverse osmosis removes water from the impurities. It does that by forcing water through a specially constructed, semi-permeable, nonporous synthetic membrane (usually cellulose acetate) that separates soluble and suspended particles from the water. The process removes a wide variety of substances from the water. More than 75 percent of minerals such as sodium, calcium and chloride may be removed from the water. Reverse osmosis also may be effective in removing fluoride, nitrate and some forms of arsenic. The membranes may last a year. Effective membrane life depends on quality of water entering the unit.
Reverse osmosis units are expensive because of the number of accessories needed to operate them. They require in-line installation and a pre-filter to remove dirt and sediment. If a backflush system is employed to prevent a buildup of contaminants on the membrane, the purchase price increases. The product water passes through to a holding tank. The process is slow and wastes 3 - 9 gallons for every one-gallon of drinking water produced. It is, however, one of the most efficient filtering systems available.
Before making the decision to purchase a water-filtering device, the water should be analyzed for impurities. The local health department or a private water-testing laboratory can perform these tests. Charges are based on the number and kinds of tests performed. If taste, odor, and THMs are the major contaminants, a device with a carbon filter could remove much of the objectionable odor and/or taste. Some carbon filter units remove more than 50 percent of the THMs. If sediment is present in high levels, a fiber filter may be needed. If a large number of impurities (excluding bacteria) or undesirable contaminants are present, a reverse osmosis unit may be the best type of filtering unit to purchase, although the cost of these units and the space needed for installation may preclude purchasing.