Home Water Treatment Introduction

Home water treatment systems can generally be divided into three categories:

  • Water softeners
  • Reverse osmosis treatment systems
  • Point of use filters

Water softeners typically are used to solve the problem of “hard water” which poses some problems but is generally viewed as a nuisance and not a health hazard.  Hard water is water that contains the dissolved solids of calcium carbonate and/or magnesium carbonate.   The most common problems occurring from hard water are diminished effectiveness of soaps, detergents and shampoos.  Hard water will also result in the carbonates solidifying on plumbing fittings and fixtures, often referred to as lime deposit.  In severe cases the lime deposits will interfere with water valves and appliances, especially water heaters and boilers. 

Reverse osmosis and point of use filters are used to remove impurities, chemicals, bacteria, etc. from water to improve water quality.

Water Softeners

water softenerParts of North America have what is often referred to as “hard water,” and people who live in these areas cope with the problems that hard water creates. It is worth noting that while most Americans believe they have hard water, less than half of homes are known actually have this problem.   In general, water above 7 grains of hardness (120 ppm) is considered moderately hard water.  Water quality greater than 10 grains (171 ppm) is considered very hard water; sometimes resulting in severe damage to water appliances and equipment over time.   Your water supplier or agency can tell you the typical hardness of the water it delivers, though the quality of the water varies somewhat throughout the year.   Hard water deposits in water heaters and boilers can cause significant energy inefficiencies, causing energy use to increase by 25% and more.  The most common defense against hard water is to install a home water softener.

Water softening involves exchanging calcium and magnesium minerals present in the water-which cause the hardness-with sodium or potassium (less common). As the water softener processes gallon after gallon of hard water on a daily basis, the treatment capability of the softener becomes depleted and must be recharged or regenerated.  This process uses water to purge and rinse salts.  Regenerating the unit uses a large quantity of sodium-rich water, called “brine,” that must be disposed of down the sewer or into a septic system.  

While water softeners offer a great solution to mitigate the effects of hard water, the disposal of the brine might have a negative effect on the quality of the wastewater effluent, especially where the wastewater agency treats and delivers reclaimed (or recycled) water as a means to offset potable water demand.  Some such agencies claim the brine from the water softeners impairs the quality of reclaimed water, making its use for irrigation less desireable; others dispute this claim so research continues.  In response to environmental concerns, potassium water softeners offer an alternative to salts, but potassium also has some detrimental environmental effects. 

In summary, calcium carbonate in the water could have some negative effects in your plumbing system and water appliances. The homeowner needs to evaluate the benfits and costs of purchasing and maintaining a water softener versus the benefits the softener provides.  Many homes benefit from water softening, while many home do not receive benefits greater than the costs.  It is important to consult with your water provider before making a decision on water treatment.

Reverse Osmosis Treatment Systems

reverse osmosisReverse osmosis (RO) is a separation and water treatment process that uses pressure to force water through a membrane that retains the solute on one side and allows the purified water to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions).  As the membranes get clogged with the matter filtered from the water, the system must go through a rinse cycle to clean the filter.  Water used in the rinse cycles can equal 25% to 75% of the amount of filtered water the system produces.  It is important to use the RO water judiciously to minimize water waste, as every gallon of water RO water produced can require input of 1.75 gallons potable water.

Point of Use Filters

point of use filterSmall water filters that attach to an individual faucet or filter water into a dispenser are called point of use filters.  These devices are primarily used to remove chemicals and metals such as chlorine and lead. Water filters can be used for preventative health reasons in the case of harmful substances, or for reasons of aesthetics, to improve the taste, color or odor of drinking water.

A number of different filter types are available for use in the home, including granular activated carbon filters, metallic alloy filters, microporous ceramic filters, and carbon block resin.

Water Use

The home water treatment systems that consume water in the treatment process are reverse osmosis systems and water softeners. Point-of-use water filters that attach to the kitchen sink faucet do not consume any water.

The amount of water consumed by a home water treatment system will vary depending upon the type and size of the system. The manufacturer should be able to provide water consumption values.

In a study of residential water use conducted for the American Water Works Association Research Foundation, 8% of the study homes were equipped with a home water treatment system that had some consumptive use. There was tremendous variability in these treatment systems. Consumptive use ranged between 1.0 gallon (3.8 L) and 74.0 gallons (280 L)of water per day. The average water use for homes equipped with a home water treatment system was 15.8 gallons per household per day (59.792)(Mayer, et. al. 1999). This provides a range of water use that might be expected from a home water treatment system.

Water Treatment and Drought Response

Many home water treatment systems such as point-of-use filters do not consume any water and hence are really not the subject of best use practices and drought actions. The information below pertains only to home water treatment systems that consume water such as reverse osmosis systems and some water softeners.

If you have a water softener or reverse osmosis system that consumes water in the treatment process you have only 2 choices during a drought:

  1. Leave the system on; or
  2. Shut the system off.

On most systems you will not be able to reduce the amount of water consumed in the treatment process.

If you opt to leave the system on, make sure that the regeneration and cleaning processes (the water consuming elements of the treatment system) are programmed to occur overnight between 2:00 and 5:00 a.m. when there is very little other water use occurring inside the house.

If you turn the system off there may be complications for starting it back up again. Consult your instruction manual or contact the system dealer if you have any questions about this process.

Water Treatment and Energy Use

Strange as it may seem, some home water treatment systems use energy. The home water treatment systems that use energy in the treatment process are reverse osmosis systems and water softeners. Point-of-use water filters that attach to the kitchen sink faucet do not consume any energy.

Water softeners and reverse osmosis systems vary in their use of energy. In both types of systems, energy is used for pumping water for flushing and regeneration. The amount of energy used depends upon the system, the quality of the water being treated, and the amount of water used in the home. Be sure to request energy consumption information from the dealer before purchasing any water treatment system or water softener.

In severe hard water environments, water softeners can improve the long-term energy efficiency of water heaters and boilers by preventing the build-up of scale or lime, which impairs heat transfer from the burner to the water. 

Purchase Tips

Information here is provided to guide individuals in evaluating the need for treatment and equipment prior to purchase. The extent to which manufacturers and dealers are willing to answer questions in a way consumers can understand will help them make informed choices and decisions.

Reports of water contamination have raised consumer awareness and concern about the safety of all water sources, both public and private. Manufacturers and dealers of home water treatment equipment are responding to the perception of unsafe water. An increasing number of manufacturers offer an ever-expanding array of products that promise to make water safe, or "pure." The consumer is left to sift through the claims and supporting data when selecting treatment methods and products.

Public water suppliers, such as cities, utilities, or rural water districts, must meet federal and state safe drinking water criteria and must notify consumers if a contaminant affecting health is found to exceed the standard. In some cases, the supplier may be required to provide an alternate water supply.

Private water supplies, on the other hand, are not regulated or tested. Individuals with private wells are responsible for protecting the water supply from contamination, testing to be sure of its safety, and selecting treatment when needed.

What should treatment equipment remove from water?

Be specific about what you want to accomplish with home water treatment equipment. Rely on independent water tests to identify and evaluate specific contaminants. There is no single device or method that removes everything or solves every water problem, regardless of the claims. In any case, it is generally not necessary to remove everything.

Triple distilled or deionized water, which is about as pure as is commonly possible, is aggressive at dissolving materials and has a flat, flavorless taste. Also, deionized or distilled water must be contained in glass or high-quality stainless steel to avoid picking up flavors from plastic, rubber and other materials.

What water tests should be done to evaluate the need for treatment?

Tests can be done for hundreds of contaminants, but they are expensive and there is no routine test for everything that may affect health.

For private water supplies, an annual test for bacteria and nitrate is the minimum advised. You, the user, must decide if other contaminants are a concern, and seek appropriate tests. It is wise to confine tests to contaminants used in the vicinity of the supply, those found locally, or other contaminants you believe may be in the water.

Public water supplies are tested regularly, and test results should be available from the supplier. These tests are excellent sources of information because they are repeated regularly. A single test may not be representative of the average water quality over the useful life of the equipment so it is important to determine a record over time.

For private water supplies, the owner or user is responsible for water testing. Owners are advised to verify all tests used for selecting and sizing equipment by having a second test from another qualified laboratory.

Are the free water tests provided by equipment dealers accurate?

There is no single test to determine if water is safe. Though most water treatment dealers can provide free in-home or laboratory tests, the tests normally are for nuisance contaminants such as hardness, pH, iron, manganese, sulfur and total dissolved solids. Occasionally a dealer also may test for nitrate. Seldom does any test include all the contaminants covered by the Safe Drinking Water Act (SDWA) standards.

As an example, testing for pesticides or volatile organic chemicals requires special laboratory procedures and is infrequently provided by equipment dealers. The free tests are okay for selecting treatment for many nuisance problems, but they don't provide all the information needed to tell if the water is safe to drink. Even in the case of nuisance problems you may want to make a second verifying test.

Beware of unscrupulous salespeople. Some salespeople conduct on-site demonstrations they may refer to as “tests”. These demonstrations typically cause precipitates to form in the water, or cause color changes to occur. Though dramatic with hard water or iron, they are generally meaningless in quantifying how much contaminant is present. But salespeople may try to convince potential buyers these are good reasons to purchase their water treatment equipment. Buyers should insist upon confirmation from an independent source before investing in equipment or water treatment services.

Does this water quality problem require whole house or only single-tap treatment?

Most nuisance problems such as iron, manganese, hardness, pH, and odor, suggest whole house or point-of-entry solutions. Some contaminants that affect health, such as nitrate and lead, are a concern only for water used for drinking or cooking, so point-of-use equipment at a separate tap that treats a few gallons daily is adequate.

Other contaminants such as bacteria and some organic contaminants will require point-of-entry equipment to prevent exposure during bathing or other water uses.

Is a second opinion on treatment procedures and equipment necessary?

Consider a second opinion on recommended water treatment equipment. Check with at least one additional dealer to see what treatment procedure and equipment is recommended, and ask questions. Compare at least two brands, and consult other references such as Consumer Reports Buying Guides.

Are products and manufacturers rated by independent tests?

The National Sanitation Foundation (NSF), a non-profit organization, has established the following standards affecting drinking water treatment equipment.

STD 42   Drinking Water Treatment Units -- Aesthetic Effects
STD 44   Ion Exchange Water Softeners
STD 53   Drinking Water Treatment Units -- Health Effects
STD 58   Reverse Osmosis Drinking Water Treatment Systems
STD 62   Distillation Units

Products that have been tested or evaluated by NSF to meet the minimum requirements are entitled to display the NSF listing mark on the products or in advertising literature for products. Manufacturers and models that meet the applicable standard are included in a listing published twice a year.

NSF listing is similar to Underwriters Laboratory (UL) for electrical product safety. Current NSF certification listings can be obtained by visiting the NSF website.

Water Quality Association (WQA) is a non-for-profit, non-governmental organization that evaluates and certifies drinking water treatment units to the appropriate standards. For education on different technologies and for a certified product listing consumers can go to WQA website

The EPA requires products containing active ingredients controlled under the Federal Insecticide, Fungicide Rodenticide Act (FIFRA) to display an EPA manufacturing facility number and product registration number. These EPA numbers mean the active ingredient added to the equipment complies with FIFRA regulations. EPA does not test or evaluate the performance of the equipment so do not interpret the EPA registration as a product test.

Ask the sales representative which standards the product meets. Ask also for test results showing removal of the specific contaminant(s) you need or want to remove. Tests by third party organizations (those neutral to and trusted by all interests served) should provide extra confidence.

Some companies may make unsubstantiated statements and claims about their products. If it sounds too good to be true, there is a strong possibility it is not true.

What should I look for in a manufacturer or dealer?

Always try to purchase water treatment equipment from a reputable local company that will be available to provide service and repair or replacement parts, and from manufacturers that stand by their products. Avoid dealers or manufacturers who may be out of business later, when repairs or services are needed.

Avoid the high-pressure salesperson with "today's special." If you must sign up that day to obtain the special, you are being pressured. Local merchants who expect to be around do not mind consumers taking time to decide. They intend to be there when you need help, so whether you buy today, next week or next month, makes little difference.

Should I rent the equipment before buying?

Renting or leasing equipment before purchasing has several advantages. You will gain experience with the responsibility of owning, operating and maintaining the water treatment equipment before you make the purchase. Renting is also an ideal solution for a temporary or short-term need to improve water quality.

Be sure you understand the terms of the rental or lease agreement. Questions to ask when renting or leasing equipment include: Who is responsible for maintenance? What is the minimum rental term? Does rent apply to the purchase price if I decide to buy? Who is responsible for insurance?

Is bottled water a preferable option?

Bottled water from the store or from a known safe source offers the benefits of no equipment to buy, operate and maintain, and no lengthy commitment for improved quality. It is an excellent temporary option when guests come, when an infant needs water that meets the nitrate standard, or other situations. It may be more cost-effective than owning and maintaining equipment, even over a long term when water use is low.

What is involved in operating and maintaining treatment equipment?

Virtually all water treatment equipment requires maintenance and service. The more treatment equipment you have, the greater the responsibility.

In recent years, manufacturers have been offering more automated and self-monitoring features to help the busy owner with the responsibility of operating and maintaining the equipment. Unless you are unusually dedicated, the automated and self-monitoring features or dealer's service agreement are recommended to ensure good operation. Many systems require periodic cleaning or replacement of components, such as filter cartridges.

What testing or monitoring equipment is needed to ensure proper operation?

Almost all water treatment devices require some monitoring or testing to evaluate and ensure proper operation. As the owner or user of a home water treatment device, monitoring to ensure proper operation is your responsibility. This usually requires special equipment. Manufacturers frequently offer monitoring equipment either as part of the package or as an option. Ask questions about what test you need to do, what test equipment you need, and if it is part of the treatment package.

What service intervals and costs are involved with this equipment?

Regardless of whether you or your dealer provides the service, there is a cost. Filters must be changed, materials added as needed, and the water checked regularly to be sure things are working. Unserviced equipment may contribute to increased levels of some contaminants. Find out what supplies and equipment are needed, and the expected costs.

Will the unit produce enough treated water for my daily needs?

Carefully consider manufacturer and dealer claims for capacity. If one brand seems to offer unusually high capacity for the size and price, it may be overstated. If the units do not function as claimed, is there a refund or exchange policy? If the dealer makes a promise, ask for it in writing! Ask others who are using the equipment about their satisfaction with it.

What is the expected life for the equipment? What does the warranty cover?

Be certain you understand the warranty and what comments it covers. If your water has contaminants that may shorten equipment life, is that covered by the warranty? Has the dealer had experience with this equipment or are you relying on the manufacturer's promise? Does the warranty cover the cost of installation?


The purchase of water treatment equipment is a decision that must be carefully considered. Whether the purchase is being made to improve the aesthetic characteristics of the water or to address health considerations, many factors must be determined.

The following are some key steps to use in selecting equipment.

  1. Correctly identify the problem to be addressed using appropriate tests.
  2. Identify options for correcting the problem.
  3. Decide whether whole house or single-tap treatment is needed.
  4. Select a reputable dealer.
  5. Obtain a second opinion.
  6. Check to see if proposed equipment has been tested or validated by independent organizations such as the National Sanitation Foundation or Water Quality Association.
  7. Talk with others who have the same equipment you may purchase.
  8. Be sure to know all the costs of the equipment: purchase price, installation, operating, and routine required maintenance,
  9. Understand what maintenance will be required
  10. Understand how to determine if the equipment is operating satisfactorily.
  11. Determine if the system has adequate capacity for your needs.
  12. Determine the expected life of the equipment and components.
  13. Understand any warranty provided with the equipment.

Available Water Treatment Processes

Activated Carbon

Activated carbon (AC) is commonly used to remove organic contaminants from water. Common organic contaminants are pesticides, industrial solvents such as trichloroethylene, and components of gasoline such as benzene. The contaminants interact with the large surface area of the AC by a process called adsorption. AC has also proven effective for removal of radon and many natural organic compounds that can cause unpleasant tastes and odors.

AC treatment systems use replaceable cartridges containing granular or powdered block carbon. Cartridges with the most carbon remove the most contaminants and last the longest, thus increasing the time between cartridge replacement. Tests show that under-the-sink models have more carbon, greater convenience and better performance than faucet and countertop models. Cartridge life expectancy can be maximized, and replacement costs minimized, with systems that allow dispensing of unfiltered water at the tap for purposes other than drinking or cooking.

The following considerations are important when purchasing AC filters; 1) contaminant removal efficiency, 2) ease of cartridge replacement, 3) effectiveness of attached sediment filters, which prevent cartridge clogging, 4) amount of pressure loss at the faucet caused by the filter, and 5) risks associated with possible bacterial growth on AC.

Ion Exchange

Ion exchange works by exchanging a compound in the water for a chemical on the filter resin. It is effective for treatment of ions or charged contaminants. Most inorganic compounds can be removed by ion exchange, however, most common organic compounds cannot effectively be removed. Ion exchange is most commonly used to remove compounds which are of esthetic rather than health concern.

Water softeners are the best known examples of ion exchange systems. Water softeners soften water by removal of calcium and magnesium which make water hard. These hardness ions in water are exchanged for the sodium ions attached to the resin surface. The water softener will no longer be effective when all sodium ions on the resin have been replaced by hardness ions. At this time, it is necessary to recharge the resin with sodium. This is accomplished by flushing the resin with high concentrations of salt (sodium chloride).

There may be some health risks associated with consuming the exchanged sodium ions from home water softeners for people with high blood pressure and heart disease. These people should check with health care professionals to determine if their maximum allowable intake of sodium will be exceeded by using a home water softener.

Ion exchange systems have also been developed for removing nonhardness chemical ions, such as nitrate and metals. Recharging the resins, in these cases, can only be done at special facilities, making this form of treatment expensive.

Reverse Osmosis 

Reverse osmosis (RO) is a membrane separation process, employing a very thin membrane which allows water through but not various undesirable chemicals. RO membranes can remove all major types of contaminants including bacteria, metals, nitrate, and organics. However, there are some organic chemicals that may not be removed very efficiently.

A RO system works by applying a high pressure to the contaminated water, forcing pure water through the membrane. Pure water collects on one side of the membrane while pollutants accumulate on the other side. The pollutants are periodically flushed to the sewer or septic system. RO membranes should last at least one year before replacement is needed.

The typical RO system consists of a sediment filter which protects the RO membrane, the RO module, activated carbon (AC) prefilters to remove chlorine for chlorine sensitive membranes, AC postfilters to remove some organics, a tank for water storage, and provisions for waste flow to drains. RO units are generally located at the point of use because of the small volume of water treated. They are typically located under the sink or on the countertop. Pretreatment with water softeners is often recommended for extremely hard water. Regular replacement of pre and postfilters is required.

An important factor to consider regarding RO is the large volume of water that is wasted. This can be on the order of 25-60 gallons per day (94.6 L to 227.1 L), depending on the amount of treated water needed and the pressure drop across the membrane.


Distillation relies on evaporation to accomplish water purification. It removes inorganic compounds, such as lead and nitrate, and some organics that do not easily evaporate and so are left behind in the distillation process. During distillation the water is heated to form steam. The steam is cooled and condenses to form purified water. Unevaporated contaminants are left behind and periodically flushed to the septic or sewer system.

Distillers are point-of-use (POU) systems and may be countertop, wall mounted, or placed on carts. Systems can be manual or automated, either, partially or fully. Some models can separate volatile organic compounds before distillation. An advantage of distillation for use on water supplies that have not been chlorinated is that disinfection occurs during boiling. Care must be taken to avoid recontamination of the condensed purified water in the storage container by bacteria.

Problems associated with distillation include loss of beneficial minerals from water and water that may taste flat. Operating costs may be higher than other forms of home treatment. Production of heat from a distiller may be beneficial in the winter but a disadvantage in the summer.

Chemical Oxidation

Chemical oxidation works by chemically changing the pollutant to a compound that is less objectionable. Chemical oxidants also act as disinfectants by killing bacteria and viruses. Chlorine is a common oxidant that is added to most public water supplies for disinfection purposes.

There are several strong oxidizers that may be practical for home water treatment of a bacteria contaminated water supply. These include hypochlorite or hypochlorous acid and hypobromite or hypobromous acid. They are available in powder or liquid form. Automatic feeders are used to add the chemicals directly to water in the pipes. They can be either point-of-use or point-of-entry systems. Adequate contact time is essential to ensure disinfection.

Chlorinated oxidants can impart an unpleasant taste to the water and may produce potentially harmful chlorinated organics (trihalomethanes) by reacting with natural organic materials present in the water.

Ozone is another chemical oxidant. It can destroy bacteria in drinking water without creating the taste and odor problems common with chlorine. In addition, many organic compounds can be partially or completely oxidixed by ozone with no formation of chlorinated compounds.

The effectiveness of an oxidant can be influenced by water temperature, acidity, concentration of oxidant, contact time with the oxidant prior to water use, and other factors. Pretreatment may be required for turbid water.

Ultraviolet Radiation

Ultraviolet (UV) radiation disinfects drinking water by killing microorganisms. Sufficient levels of UV radiation must be applied or it may merely retard growth or impede reproduction of bacteria and viruses, rather than destroy these organisms.

UV systems are placed directly into water lines at convenient locations for POU or POE treatment. UV should be the final treatment if it is combined with other technologies. The other devices can remove dissolved and undissolved materials which inhibit the disinfection process and UV can kill any bacteria left in the system.

A UV disinfection system consists of a prefilter for sediment removal in addition to a UV-emitting lamp. Good designs should provide 1) maintenance with easy tube and lamp removal, 2) flow rates that provide adequate contact time between radiation and bacteria and 3) easy visual inspection of the lamp and tube.

The primary advantage of UV treatment is that no disinfecting chemicals are added. Taste and odor problems are less likely to arise when chlorine is not added. However, chlorine provides residual disinfecting power downstream of the application point while UV provides no such residual.

Information presented here was adapted from "Buying A Home Water Treatment Unit" FACTS For Consumers From, Bureau of Consumer Protection (accessed 6/8/01), the Kansas State University Cooperative Extension Service Fact Sheet "Questions to Ask Before Buying Water Treatment Equipment" (accessed 6/8/01), the University of Nebraska Institute for Agricultural and Natural Resources, and Michigan State University Extension (accessed 6/8/01), MSU Extension Water Quality Bulletins (accessed 6/8/01).