Reviewed October 1993
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Concern about drinking water quality intensified in the early 1970s. Media accounts told of trace elements slipping through filters in municipal water treatment plants. Reports indicated toxic wastes had seeped into some wells. This concern prompted Congress to pass the Safe Drinking Water Act in 1974. The act mandated standards -- maximum contaminant levels (MCL) -- for inorganic chemicals such as arsenic, barium, chromium, coliform bacteria, nitrate and 12 secondary contaminants.
Secondary contaminants include foaming agents, chlorine, iron, manganese, odors and total dissolved solids. These substances in small quantities can impart a disagreeable odor and taste to water. One group of these contaminants, trihalomethanes (THMs) -- chloroform, for example -- has been found to be cancer-causing in some laboratory tests on rats. THMs form when the humic acid in organic matter reacts with chlorine used for disinfecting drinking water. This reaction occurs when the chlorine is added before the sedimentation stage in the water treatment process.
The Safe Drinking Water Act was amended in 1979 to require community water systems serving 10,000 or more persons to analyze for THMs when a disinfectant (chlorine) is added to the water. THMs are more likely to occur in areas using surface water because of the higher possibility of organic matter being found in surface water supplies than in deep ground wells.
Approximately 55,000 of the 61,000 public water facilities in the United States meet the standards mandated by the Safe Drinking Water Act and administered by the Environmental Protection Agency. Home treatment of water provided by these systems should not be needed unless the water is hard, has disagreeable odors and/or tastes or has other minerals not removed to a satisfactory level by the water treatment. People concerned about the quality of their drinking water, or who dislike their water, may wish to consider using one of the many home water treatment devices available.
Three major types of water treatment devices are available: filters, distillers and softeners. Filtering devices are discussed in this guide.
Three kinds of filtering devices are available. Carbon filters are found most frequently. The second most common uses fiber filters. The third and most expensive type is a reverse osmosis unit.
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.
Five carbon-filtering devices are summarized in Table 1.
Table 1
Water filtering devices using activated carbon.
| Type | Options | Installation1 | Uses2 | New3 | Replacement3 |
|---|---|---|---|---|---|
| Faucet mount | "Remote" filter on counter | To faucet head from which aerator has been removed | Removes odor, bad taste, some THMs and other chemicals | $20 to $190 | $4 to $50 or more |
| Portable (pour through) | Options: Pump, Single or multi-layered filters, Size of holding tank | If powered, to a 12 or 115 volt line, No plumbing | Removes odor, bad taste, some THMs, some bacteria if chlorine in filter or if oxygen is bubbled through water | $10 to $275 | $2 + |
| Specialty | Not applicable | In cold water line to refrigerator, standard ice maker, humidifier or water heater | Removes sediment, odor, bad taste | $12 to $90 | $12 to $16+ |
| Line by-pass | Two locations | In water line near where enters house, to cold water line with a pipe leading to a separate faucet at kitchen sink, Shut off valve | Removes odor, bad taste, some THMs and other chemicals, sediment | $35 to $150 or more | $8 to $30 |
| Stationary (under sink) | One or more cartridges, By-pass faucet kit for some models | Icemaker line | Removes odor, bad taste, some THMs and other Chemicals | $25 to $400 | $7.50 to $40 or more |
Fiber filters designed to take out turbidity (suspended sediment) contain spun cellulose or rayon. 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.
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 such minerals 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 prefilter to remove dirt and sediment. If a backflush system is employed to prevent a buildup of contaminants on the membrane, the purchase price increases.
Contaminants to be removed
Water from the tap is not "pure". Water can form solutions with many substances, and undissolved substances will remain suspended in the water. Water's distinctive taste comes from the impurities and can include contaminants with disagreeable tastes and odors. These contaminants may be harmful.
Before making the decision to purchase a water filtering device, the water should be analyzed for impurities. The local health department (usually located at the county seat) 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.
Location
Two choices are in-line (faucet-mounted, line by-pass, stationary) or portables. Installing in-line units may simply mean removing an aerator in a faucet and attaching the filtering device, or it can mean adding branch lines and valves. Some line by-pass and stationary models require installation by a licensed plumber. The reverse osmosis units should be installed by a plumber.
Space available
In-line devices vary in space needed. Faucet-mounted units require clearance for the unit above the sink or space on a counter. Units under the sink require clearance space for the unit, branch lines and valves. This space may not be available if a large disposer is installed under the sink. The reverse osmosis units require space for the prefilter, the units, a water reservoir, valves and additional line connections. One cubic foot or less is needed for portable units.
Maintenance
All except a few models of filtering units require replacement of the filtering medium. Except for specialty devices (see Table 1), the frequency of cartridge replacement is lower for the larger, more expensive units than for the smaller units. The effective life of a unit varies with amount of water filtered and quantity of impurities in the water. Some of the higher-priced units contain a back-washing system that manufacturers claim eliminates the need for replacement cartridges. Water at 145 degrees Fahrenheit (63 degrees Celsius) is necessary for the back-washing system to be effective.
Features
The number of cartridges in carbon filtering units varies from one in most faucet-mounted units to one or more in stationary, under-the-sink units. The form and quantity of carbon used also varies. Carbon types include granular, powder in block and powder in pad. A private testing organization found that the powder-in-a-pad type was less effective than other types. Granular is the most popular type of carbon. The cartridges in faucet-mounted units are smaller and contain less carbon than the under-the-sink units. The design of the cartridge for the under-the-sink units should force the water to travel the length of the cartridge for good filtration. Time for effective filtration varies.
The cartridges in faucet-mounted units may last from one to 12 months The larger amount of carbon in the under-the-sink units may effectively remove contaminants for six months to a year or longer. A few models feature a replacement indicator. Most filters come with manufacturer- suggested observations of how to determine the effectiveness of the cartridge. Look for color change in the cartridge, reduced water flow or return of bad taste or odor as depletion indicators. However, metering is seldom practical outside testing laboratories.
Integral or optional by-pass valves provide a means of obtaining unfiltered water for nondrinking and noncooking uses. An optional by-pass faucet kit may cost $35 or more. Allowing water to run through the filter for at least 30 seconds before filling a container helps to remove bacteria that may have accumulated within the filter.
Some filters may contain silver. Manufacturers claim that silver discourages the growth of bacteria within the filter. The Environmental Protection Agency, however, has concluded that silver compounds in water filters have little bacteriostatic effect.
Cost
Carbon filtering devices vary in price from $10 to $400 or more. Fees for a licensed plumber increases the initial cost of some models. Replacement cartridges range in price from $3 to $50 or more. Reverse osmosis units vary in price from $300 to $900. Installation cost may be included in the purchase price of reverse osmosis units.
GH4864, reviewed October 1993