People have become increasingly concerned about the quality of their water, including the possibility of contamination with hazardous substances. Sources of this contamination are solvents, pesticides, household cleaners, industrial wastes, and underground storage tanks. Chemical compounds, including methylene chloride, trichloroethylene (TCE), lindane, benzene, chlorobenzenes, carbon tetrachloride, and vinyl chloride have also been found in water supplies. Chlorination of drinking water can produce trihalomethans (THMs), which may be a cancer causing substance, according to some research. Radon, a radioactive decay product of natural uranium, is found in groundwater as well as in the air of buildings and have been correlated with an increase in lung cancer.
Private well owners are particularly vulnerable to drinking water contamination. It has been thought that groundwater was not easily contaminated because soil could effectively purify water moving through it. Recent evidence shows that soil is not the buffer for chemicals it was assumed to be.
Under certain circumstances, toxic compounds can leach through soil into groundwater and eventually enter household well water.
Well-closings of municipal and rural systems with disease-causing source waters, as shown by the news media, indicate they are carefully monitored. However, individuals on private systems have the responsibility to determine independently whether their drinking water needs treatment.
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. Water quality involves the degree of acceptability for household uses such as drinking, cooking, bathing and laundering. Water conditioning equipment improves quality by reducing turbidity (suspended sediment), reducing hardness, removing disagreeable odors and/or tastes, reducing minerals and possible contaminants.
Four common types of water treatment systems to improve water for household uses are: filters, reverse osmosis units, distillers, and softeners. Filters and reverse osmosis systems are discussed below.
Dirt, sediment, and odors can be removed from water by using filters. Adsorption and mechanical filters are available. Carbon filters are the most common adsorption filters. Fiber filters are the most common mechanical filters.
Carbon filtering devices use activated carbon (cartridges) with a porous surface to collect dissolved organic compounds including TMHs, odors and disagreeable tastes.
A filter’s effectiveness depends on 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 decreases less rapidly over time that it does for those containers with a small amount charcoal.
A typical activated carbon cartridge is a cylinder holding approximately one cubic foot of carbon. The form and quantity of carbon used varies; they can be granular, powder in block or powder in pad. Tests by a private testing organization indicated the powder-in-a-pad type was less effective than other types. Granular is most frequently used. The cartridge sides should be rigid (hard plastic or stainless steel) to force water through the length of the column bed. Cartridges with sides of mesh or wound string allow water to bypass extensive contact with the carbon.
Location of the treatment unit in the home depends upon its intended function. Users may choose from six models: 1) pour through, 2) faucet mount, 3) in line, 4) line bypass, 5) specialty, 6) point of entry (POE). (See Figure 1).
Pour through is similar in design to a drip coffee maker, and is the simplest type of activated carbon filter. A quantity of untreated water is poured through the carbon and treated water is collected in a receptacle. The units are not connected to the water supply and usually sit on the counter. They are portable, require no installation, and are convenient for camping and picnicking. Pour-through devices will treat only small quantities of water at a time and are not as effective as larger, automatic units.
Faucet mount units are attached to the faucet (usually in the kitchen) or placed on the counter with connections to the faucet. There are two basic designs. One is the bypass option which has a valve to filter water used for cooking and drinking, and prolongs the life of the carbon cartridge. In contrast, the nonbypass option filters all water passing through the faucet. Because the quantity of carbon contained in a faucet-mount unit is not large enough to provide extensive contact with the water, these devices are not recommended for removal of toxic organics.
The in-line device is installed beneath the kitchen sink in the cold water supply line; bypassing the unit for uses other than drinking or cooking is not an option. If both hot and cold water come from a single spigot, the treated (cold) water can mix with the untreated (hot) water. Treated water is assured only when using cold water for drinking and cooking.
The line-bypass unit is also attached to the cold water pipe, but a separate faucet installed at the sink provides treated water for cooking and drinking. The regular tap delivers untreated water. This design increases the life of the carbon by allowing a choice of treated or untreated water, depending on the intended use.
Specialty filters such as ice maker and scale filters are placed on the cold water supply line to appliances. Ice maker filters are attached to the cold water line to refrigerators or standard ice makers. Scale filters are connected to the supply line to water heaters or humidifiers.
A point of entry (POE) device treats all water coming into the residence. There is no bypass option although water can be tapped prior to filtration to provide for outdoor, nonconsumptive uses. The POE device is recommended for treatment of volatile organic compounds (VOCs) in concentrations above established standards. Since VOCs easily vaporize from water into the air, POE treatment prevents inhalation of hazardous vapors from the shower, dishwasher or washing machine or exposure through skin contact. This device should meet certain guidelines concerning the application rate of water to the carbon, contact time between the water and the carbon, the type of carbon used, and the wastewater discharge. Specific recommendations are obtained from local health departments.
Cost: Carbon filtering devices vary in price from $10 to $400 or more. For some models, cost of installation by a licensed plumber must be added to the purchase price. Replacement cartridges range in price from $3 to $50 or more.
Fiber filters contain spun cellulose or rayon and are designed to take out turbidity (suspended sediment). The tightly wrapped fibers form a cylinder around a tubular opening and line pressure forces water through the wrappings to the inner opening that leads to the faucet. After the fibers tap silt, filtered water passes to the opening that leads to the faucet. Fiber filters come in various meshes from fine to course with the lower micron rating being the finer. The finer the filter, the more particles will be trapped, requiring more frequent filter change.
Cost: Fiber filter systems run about $25 to $1400, depending on whether they are a simple faucet attachment or connected directly to the plumbing for whole house treatment.
Reverse Osmosis Units
A reverse osmosis unit is effective in removing a wide variety of inorganic chemicals, such as nitrates, calcium, and magnesium. A reverse osmosis unit is up to 95 percent effective in removing inorganic contaminants. However, reverse osmosis units also remove beneficial chemicals such as fluoride. Typically, a reverse osmosis unit is used to treat water only for drinking and cooking.
A reverse osmosis system typically includes: a pre-filter to remove sediment; an activated carbon filter to remove odors and taste; a semi-permeable membrane through which water flows under pressure; a tank to hold the treated water; and a drain connection for discharging concentrated contaminants. Different size reverse osmosis units are available. They may be located under the sink, counter top or in a remote location, depending on the size of the water holding tank. The capacity of the reverse osmosis system, in gallons per day, would need to be matched to household water needs. Most households find five gallons per day adequate.
Cost: A reverse osmosis unit ranges in price from $200 to $400 for counter top and $600 to $1,000 for under-counter unit, but renting can be an option. The cost of a reverse osmosis unit needs to be weighted against the type and quantity of contaminants in the water, and the concern for safety. Further, the cost of a reverse osmosis unit should be compared to other alternatives such as bottled water.
Choosing a Treatment System
Tap water is not “pure” water. Water can form solutions with many substances and these undissolved substances may remain suspended in the water. Impurities give water its distinctive taste, but impurities can include contaminants which impart disagreeable tastes and odors to water and are harmful as well.
Before making the decision to purchase a water filtering device, the water should be analyzed for impurities that affect health. The local Health Department (usually located at the county seat) or the Texas A&M AgriLife Extension Service water-testing laboratory can perform these tests. Charges are based on the number and type of tests performed.
When purchasing a water-treatment system, the individual should consider the following:
- amount of carbon or fiber contained in the unit
- construction of reverse osmosis membrane
- initial and replacement filter or membrane costs
- frequency of filter or membrane change
- operating convenience.
Other important consideration are the potential water pressure drop in the home system after installation of a unit and the daily quantity of treated water supplied by the device.
Kind of contaminants to be removed
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. It will remove limited quantities of rust, but particulate matter or high iron levels cause frequent fouling of the unit. If sediment is present in high levels, a fiber filter may be needed.
Filters have limitations. They will not soften water or remove bacteria, viruses, dissolved metals, hydrogen sulfide, chloride, fluoride, or nitrate. Neither activated carbon nor fiber filters are recognized methods for bacteria removal.
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.
In-line devices vary in space needed. Faucet-mounted units require clearance for the unit above the sink or space on the counter. Undersink mounted units require clearance space for the unit, branch lines and valves that may not be available if a large disposer is installed under the sink. The reverse osmosis units require space for the pre- and post-filter, the R.O. membrane, a water reservoir, valves and additional line connections. One square foot (.3m2) or less space (area and clearance) is needed for portable units.
All except a few models of water treatment systems require replacement for the filtering medium to avoid a build-up of deposits. Except for specialty devices, the frequency of cartridge replacement is lower for the larger, more expensive units than for the smaller units. Effective life of the filtering medium or R.O. membrane varies with the amount of water filtered and quantity of impurities in the water. Effective use for filters range from one to 12 months; for R.O. membrane, 1 to 2 years. Some of the higher priced units contain a back-washing system that manufacturers claim eliminates the need for replacement cartridges. Water at 145 degrees F (63 degrees C) is necessary for the back-washing system to be effective.
The material in some filters provide a growth surface for bacteria. Regular use and maintenance is necessary to help prevent bacterial growth on the filter. To reduce bacterial count in the treated water, run the water for 30 seconds before water use each day, or until 1 to 2 quarts have passed through.
Water treatment can produce a clearer, better tasting and smelling water and increase its function for household use. Some water conditioning treatments also reduce other contaminants, such as nitrates, arsenic or lead, that are known or suspected health hazards. The kind of device you choose will depend on your water quality problem and budget.
- Clean Water at Your Tap. Rodale’s New Shelter. Oct. 1983, pp. 82-86.
- Hallaway, J. Drinking Water Treatment Devices: Filters. Colorado State University Extension Service: Service in Action. Nov. 1, 1983.
- Lalezary, S., M. Pirbazari and M. McGuire. “Evaluating Activated Carbons for Removing Low Concentrations of Taste and Odor-producing Organics.” Journal of American Water Works Association. Nov. 1986, pp. 76–82.
- Lykins, B.W., E.E. Geldreich, J.Q. Adams, J.C. Ireland, and R.M. Clark. “Granular Activated Carbon for Removing Nontrihalomethane Organics from Drinking Water, Project Summary.” USEPA, No. EPA-600/S2-84-165. Dec. 1984.
- Oulman C.S., V.L. Snoeyink, J.T. O’Connor, M.J. Taras. “Removing Trace Organics from Drinking Water Using Activated Carbon and Polymeric Absorbents.” EPA Project Summary. EPA-600/S2-81-977, 078, 079. Jul. 1981. Cincinnati. OH.
- Reasoner, P. Journal of American Water Works Association, 79 (10): 60, 1987.
- Ruzelle, R. Journal of American Water Works Association, 79 (10): 53, 1987.
- Wagenet, Linda, Ann Lemley. Activated Carbon Treatment of Drinking Water. Cornell Cooperative Extension, New York State College of Human Ecology. Dec. 1987.
Appreciation to Bill Bathelor, professor, civil engineering, and Ann V. Beard, Extension Clothing and Textiles Specialist, Texas A&M System, for reviewing this publication.
Written by Susan M. Quiring, Ph.D., former Extension Housing Specialist, Texas A&M AgriLife Extension Service, Texas A&M System, College Station, Texas. 1991. L-2280
Last updated: July 4, 2015