Consumers can choose from a variety of home water treatment products. In response to recent public concern of water quality, the home water treatment industry now offers many products. When faced with so many choices, consumers wonder what, if any, water treatment system they need. The various methods for treating water and some of the advantages and disadvantages of those methods are described in this bulletin. This is not an endorsement of any particular method or product for treating water in the home.
If you are on a public drinking water supply it most likely meets national safety standards and home treatment should not be needed for health protection. Home owners using a private water supply are responsible for monitoring the quality of their own drinking water supply (refer to WQ 4). Water treatment devices can improve the quality of water by reducing health hazards such as bacteria, chemical pollutants and other toxic substances, or help remove nuisance problems such as odors or hardness.
Before considering any treatment devices, you should know the quality of your water supply. Odor and hardness problems can sometimes be detected by simple observation. Detection of bacteria, potentially toxic substances and other contaminants usually requires laboratory conducted tests. If any undesirable qualities are identified in the water, the problem can often be solved by repairing or replacing the existing water system or treating the home water supply.
Locating a safe water supply is usually the best solution to combat a health risk. When persistently contaminated water poses a health threat or makes the water unusable, consider the following options: correct well construction faults, eliminate sources of contamination, install a new private well, connect to a public water supply or develop a community water system. After considering all of the options, a home water treatment system may be the most economical choice.
Before purchasing a system you should know how the various systems work, what problems they address and the maintenance required. If more than one problem exists, treating water can become complicated.
Water treatment systems generally use one or a combination of these five basic categories:
Disinfection methods kill most of the harmful bacteria, viruses, cysts and worms found in water which can cause acute illness. Disinfection methods include chlorination, pasteurization, ultraviolet light and boiling.
The most common, oldest and relatively inexpensive method used to disinfect water is chlorination. A chemical feed pump continuously dispenses chlorine chemicals into the water supply (Figure 1). Chlorine, an oxidizing agent, kills most bacteria and some viruses. In the proper concentrations and under adequate exposure time, chlorine is an excellent disinfectant.
However, care must be taken to assure only clean, clear water is used. Chlorine reacts with certain metals and organic matter in the water. The major problem with chlorination is the potential formation of hazardous, chlorinated, organic chemicals (trihalomethanes) when the chlorine reacts with organic molecules in the water supply. Using an activated carbon filter after chlorination will remove excess chlorine and limited amounts of chlorinated chemicals formed. Chlorination may also oxidize and remove some color and odor-causing substances including some iron and hydrogen sulfide.
The chemical feed pump requires frequent maintenance. The chemical reservoir must be kept filled and the pump checked at regular intervals for worn parts.
With pasteurization, water is heated to kill bacteria, viruses, cysts and worms. The limited efficiency of the heat exchange makes pasteurization expensive. Pasteurization does not leave behind a residual product which continues to disinfect beyond the immediate treatment period.
Low-pressure mercury arc lamps produce ultraviolet light which has germicidal properties. The radiation kills or deactivates pathogens. Bacteria are killed with relatively low amounts of radiation, viruses are more resistant, and cysts and worms are unaffected.
The lamp's efficiency decreases with age and must be replaced annually. Color, turbidity and organic impurities in the water also interfere with transmission of ultraviolet energy and may reduce efficiency to unsafe levels. Also, radiation leaves no residual product that continues to disinfect beyond the treatment period. Boiling
Boiling water for 15-20 minutes can reduce the number of bacteria and other microorganisms. However, boiling concentrates inorganic impurities such as nitrate and sulfates. Boiled water also tastes flat because the carbon dioxide is removed.
Filter systems are a relatively simple and effective way to control a variety of contaminants. These include mechanical filters, activated carbon filters, oxidizing filters and neutralizing filters.
Mechanical filters (Figure 2) remove suspended material from water including sand, silt, clay or organic matter. They do not remove dissolved or very fine particles and are often used in combination with other treatment equipment. Filters are commonly of fabric, fiber, ceramic or other screening material. Mechanical filters can be cartridge units, mounted in a single waterline or on a tap, or tank units, which treat an entire household water supply. The filters must be serviced periodically.
Activated carbon filters (Figure 3) absorb impurities as they pass through a carbon cartridge. They are generally used to eliminate undesirable odors and tastes, organic compounds and remove residual chlorine. Most inorganic chemicals, metals, microorganisms and nitrate are not removed by the filters.
Carbon filters also remove some potentially hazardous contaminants such as radon gas, many dissolved organic chemicals and trihalomethanes. If low levels of these contaminants exist, a whole-house unit can be used. However, these filters are not designed to remove persistently high levels of these contaminants. When contamination cannot be eliminated, an alternative water supply may be the safest solution.
The carbon filter loses its effectiveness as it becomes saturated with contaminants and must be replaced on a regular basis. Using the filter longer than its rated lifetime may cause contaminants to be flushed into the drinking water. Before purchasing the unit, ask the dealer if the filter can be replaced, the frequency of replacement, where replacement filters may be purchased and their price.
The material in an activated carbon filter provides a growth surface for certain bacteria. Although current research indicates the bacteria do not cause disease, buildup can occur over time. If the filter has not been used for five or more days, simply run water through the filter for at least 30 seconds before use.
Some manufacturers claim the addition of silver in their carbon filters will reduce or prevent bacteria growth. These carbon filters are registered as bacteriostatic by the Environmental Protection Agency (USEPA) due to a requirement by the Federal Insecticide, Fungicide and Rodenticide Act. The required registration indicates the filter does not release excessive amounts of silver. The EPA has not endorsed these methods for reducing bacteria in the filter or in the water. Furthermore, a bacteriostatic carbon filter is not adequate to treat water that is microbially unsafe.
Oxidizing filters remove iron, manganese and hydrogen sulfide (rotten egg odor). A manganese zeolite-coated filter causes dissolved iron and manganese to form particles the filter then traps. These filters are useful in removing iron if a water softener is not wanted. The filter usually treats the entire household water supply. Periodically the filter must be rinsed with a chemical solution to remove the accumulated iron and manganese.
Neutralizing filters treat acidic water. The filter treats all of the home water supply by passing it through limestone chips or other neutralizing agent. Although acidic water is uncommon in Indiana, where it does occur it can leach lead, copper or other toxic metals from household pipes into the water supply.
Two potential problems occur with the filter. First, it may increase water hardness. Secondly, acidic water may intensify any iron problems already present in the water supply. The filter requires little maintenance except the need to occasionally replace the limestone chips.
Reverse Osmosis (Figure 4) pressurizes and passes impure water through a semi-permeable membrane and removes many of the impurities (approximately 90 percent free of mineral and biological contaminants). The quality of the membrane and pressure of the water help determine how effective the water separates the contaminants.
Reverse Osmosis (RO) units remove substantial amounts of most inorganic chem- icals (such as salts, metals, minerals), most microorganisms and many organic chemicals. They do not effectively remove some organic compounds.
Mechanical filters and activated carbon filters are most always used with a RO unit. First, the mechanical filter removes dirt, sediment and other impurities which clog the reverse osmosis membrane. The RO unit is installed next. An activated carbon filter then removes organic compounds which pass through the RO unit.
Reverse Osmosis units use large amounts of water. Typically, about 75 per- cent or more of the water put into RO units is discarded with the contam- inants. These units are expensive to purchase. Usually they are connected to a cooking and drinking line only and installed under the kitchen sink. Regular testing of the water supply is necessary to make sure the membrane is intact.
Distillation (Figure 5) heats water until it vaporizes as steam. Minerals, bacteria and other substances are left behind when the steam recondenses into relatively pure water. Distillers remove bacteria, minerals, trace amounts of metals, many organic chemicals and nitrate. Some stills allow contam- inants with boiling points lower than water (some pesticides and volatile solvents) to vaporize with the water and recondense with the distilled water. A fractional distiller avoids this problem. Distillers also remove benefi- cial minerals and make water taste flat or bland.
The distillation process is very slow (daily capacity is usually between two and five gallons). Approximately five gallons of tap water is required to produce one gallon of distilled water. Stills are relatively expensive. They require frequent cleaning and may be difficult to keep clean. The maintenance requirements and electricity consumption should be major con- siderations when purchasing a distiller.
A common problem of water supplies in Indiana is hardness, mainly caused by excess calcium and magnesium. Ion exchange systems soften hard water by removing the minerals causing hardness. These hardness minerals may inter- fere with the cleaning action of soaps and detergents and cause scale buildup in hot water pipes, water heaters and fixtures. The system also effectively removes some iron, manganese and many heavy metals.
The hard water is pumped through a tank containing an exchange resin. Sodium on the exchange resin replaces the hardness minerals. The sodium remains in soluble form in the softened water.
To function properly, the resin tank must be periodically flushed (or recharged) with a solution of sodium chloride (salt). Some softeners automatically recharge the tank either on a regular schedule, or when an electronic sensor detects the resin needs to be recharged. With automatic recharge you only need to keep the sodium storage container filled. Other softeners must be recharged manually and are usually serviced by water treat- ment companies.
Before buying a water treatment system know the quality of your water supply and if treatment is needed. Consider the simplest and more economical solu- tion to the problem. Removing the source of contamination, obtaining a new source of drinking water or treating the water with a water treatment system may be appropriate solutions.
When purchasing a treatment system ask the following questions:
- Will the system address the specific water quality problem?
- How many gallons of treated water does the unit produce per day? Is the amount sufficient for your household needs?
- Is there a sufficient water supply for the treatment unit to work properly?
- How do you know if the unit is not working properly?
- What maintenance is required?
- What routine servicing is offered? Is a service contract available?
- Is there a warranty? What does it cover? Make sure any claims about the performance of the treatment unit are clearly identified in writing.
- What is the total cost? Consider the purchase price, installation cost, maintenance cost and operation cost. Every treatment system has its own advantages and disadvantages.
- If you rent the equipment, does your agreement include an option-to-buy provision?
The following table lists some of the more common treatment methods used to handle certain contaminants. This is a general guide and does not contain all of the potential treatment techniques or contaminants. The concentration of the contaminant and combination of various contaminants can have a major impact on the effectiveness of the treatment method.
________________________________________________________________________________ | TREATMENT OPTIONS | |______________________________________________________________________________| |Contaminant | Chlori | UV | Mech | Act | Oxi |Neut |Rev |Dist | Ion | Aer- | | | nation | | Filt | Carb | Filt |Filt |Osmo | | Exc | ation| |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Bacteria | o | o | | | | | | o | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Calcium and | | | | | | | | | o | | |Magnesium | | | | | | | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Hydrogen | | | | o | o | | | | | o | |Sulfide | | | | | | | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Iron and | | | | | o | | | | o | | |Manganese | | | | | | | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Lead | | | | | | | o | o | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Nitrate | | | | | | |  | o | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |pH-Acidity | | | | | | o | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Radon in | | | | o | | | | | | o | |water | | | | | | | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Sediment | | | o | | | | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Sodium | | | | | | | | | | | |Chloride | | | | | | | o | o | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| |Many | | | | | | | | | | | |Pesticides | | | | o | | | o | o | | | |and Organics| | | | | | | | | | | |____________|________|____|______|______|______|_____|_____|_____|_____|______| | | |** Activated carbon filters vary in their effectiveness to remove | | contaminants depending upon the size of the unit and | | the type and amount of contamination. | | | | Reverse Osmosis units generally remove less than half of the nitrates | | in water. | |______________________________________________________________________________| | | | Note: Mech Filt = Mechanical Filter | | Act Carb = Activated Carbon | | Oxi Filt = Oxidizing Filters | | Neut Filt = Neutralizing Filters | | Rev Osmo = Reverse Osmosis | | Distil = Distillation | | Ion Exc = Ion Exchange | |______________________________________________________________________________|
For further information on water testing or suspected contamination in your area, contact your local Health Department or county Cooperative Extension office. The following bulletins in the WQ series may also be helpful:
WQ 4 "Why Test Your Water?"
WQ 5 "Interpreting Water Test Reports Part One: Inorganic Materials"
WQ Bulletin "Interpreting Water Test Reports Part Two: Organic Materials"
Private Water Systems Handbook. MWPS-14. Midwest Plan Service.
Shaw, Byron H. and James O. Peterson. "Improving Your Drinking Water Quality". Cooperative Extension Service, University of Wisconsin-Madison, Madison, Wisconsin.
"Water Treatment Fundamentals". 1983. Water Quality Association Educational Services.
This material is based upon work supported by the U.S. Department of Agriculture, Extension Service, under special project number 89-EWQI-1-9202.
Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University, and U.S. Department of Agriculture cooperating; H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an affirmative action/equal opportunity institution.