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Water Treatment

A wide variety of water treatment systems and devices exist that remove or reduce unwanted chemicals and/or microorganisms through disinfection, physical filtration, adsorptive filtration, oxidation/reduction and chemical exchange reactions in order to make water potable or improve the aesthetics of the water.

Best available technologies (BATs) describe water treatment methods that are consider best at removing different kinds of specific chemicals and contaminants from water being used for potable purposes. Some chemicals can be removed or reduced by several water treatment methods that are all considered BATs. Many treatment methods and devices are used in combinations to improve the over-all treatment capability. Some water quality issues will require that different treatment methods be used in combination to get adequate contaminant reduction. 

Permit Requirements

Whole-house water treatment devices installed on an existing private water system for continuous disinfection and to treat for health related contaminants such as arsenic, nitrates and VOCs are required to be installed under an alteration permit obtained from the local health department. These treatment systems must also be installed by a private water system contractor registered with the Ohio Department of Health (see link).

Water treatment systems installed to treat aesthetic conditions such as hardness, high sulfur, or high iron do not require a permit to be installed and are not required to be installed by a registered private water systems contractor. 

Any treatment system installed at the point of use (POU) (such as at one sink), do not require a permit or a registered private water system contractor for the installation. 

Below are very brief descriptions of some of the more common water treatment methods. This list is not all-inclusive of all possible types of home water treatment.  There are also new products continually being developed for home water treatment. 

Information on technologies which are effective at removing specific contaminants:

Water Treatment Products Standards

The following ANSI Standards are required for water treatment products used in private water systems in Ohio.

ANSI standard 61

This standard establishes the minimum health effects requirements for the chemical contaminants and impurities that are indirectly imparted to drinking water from products, components, and materials used in drinking water systems.  The products and materials of focus:

  • Process media (e.g., carbon, sand),
  • Protective materials (e.g., coatings, linings, liners),
  • Joining and sealing materials (e.g., solvent cements, welding materials, gaskets),
  • Pipes and related products (e.g., pipes, tanks, fittings),
  • Mechanical devices used in treatment/transmission/distribution systems (e.g., valves, chlorinators, separation membranes, point-of-entry drinking water treatment systems), and
  • Mechanical plumbing devices (e.g., faucets, endpoint control valves).

ANSI standard 60

This Standard establishes minimum health effects requirements for the chemicals, the chemical contaminants, and the impurities that are directly added to drinking water from drinking water treatment chemicals.

This Standard also contains health effects requirements for chemical products that are directly added to water but are not intended to be present in the finished water.

Chemicals covered, but not limited to:

  • Coagulation and flocculation chemicals
  • Softening
  • Precipitation
  • Sequestering
  • pH adjustment
  • Corrosion/scale control
  • Disinfection and oxidation
  • Miscellaneous treatment chemical and water supply chemicals

ANSI standard 53

This Standard establishes minimum requirements for materials, design and construction, and performance of point-of-use and point-of-entry drinking water treatment systems that are designed to reduce specific health-related contaminants in public or private water supplies.

These substances are considered established or potential health hazards that may be

  • Microbiological,
  • Chemical, or
  • Particulate (including filterable cysts) by nature.

ANSI standard 55 Class A

Standard establishes the minimum requirements for the reduction of microorganisms using ultraviolet radiation (UV).

Standard covers UV microbiological water treatments systems and components for point-of-use and point-of-entry applications.

Systems certified to meet the ANSI/NSF Standard 55 Class A must be used in private water systems.  Class A systems are certified to inactivate pathogenic microorganisms, including bacteria, viruses, Cryptosporidium oocysts, and Giardia cysts from contaminated water. Class B systems are not certified to treat water from private water systems.

Organizations and Associations accredited by ANSI to certify and test water treatment products

The following organizations or associations are accredited with the American National Standards Institute (ANSI) to certify and test water treatment products under ANSI product standards 53 (filters), 55 (UV devices), 60 (chemicals for use in water) and 61 (water device components and process media).

NSF International (NSF)

Home Page - http://www.nsf.org/

Water Quality Association (WQA)

Home Page -http://wqa.org/


Home Page -https://www.ul.com/

American Water Works Association

Home Page – https://www.awwa.org/

Point of Entry or Point of Use

Water treatment can be whole-house, also called point of entry (POE) or at the point-of-use (POU) depending on the needs of the household. Whole-house (POE) treatment is installed at the pressure tank and treated water goes to all spigots and water outlets in the house. POU treatment is providing treatment to only one particular spigot location. 




Filtration  X X
Chlorine Continuous Disinfection X  
Iodine Continuous Disinfection  X  
UV Continuous Disinfection  X  
Ozone Continuous Disinfection  X  
Granular Activated Carbon (GAC)  X X
Reverse Osmosis  X X
Ion Exchange X  
Aeration  X  

Types of Water Treatment

Consult with the Local Health District and Private Water Systems Contractor about the appropriate treatment for your water.  

Continuous Disinfection - Chlorine, Iodine, Ozone, and Ultraviolet Light

  • Click here to go to the Continuous Disinfection web page.

Granular Activated Carbon

Granular Activated Carbon (GAC) is made of organic materials high in carbon such as coconut shells, nutshells, wood, or coal.  GAC filters have a tremendous surface area resulting from its highly porous structure. Its effectiveness depends on the flow rate of the water and the contact time.  GAC allows water to pass through it while adsorbing other organic materials and certain dissolved chemicals, such as: 

  • Chlorine and other halogens 
  • Volatile organic compounds (VOCs) which include:  
  • Trihalomethanes (THMs) (by-product of chlorination) 
  • Many organic solvents such as benzene, ethylbenzene, toluene and xylene (BTEX)  
  • Many organic chemical pesticides and herbicides 
  • Some harmful algal bloom (HABs) chemicals such as Microcystin toxin 
  • Some longer chain PFAS such as PFOA and PFOS

GAC is not effective for removing minerals and salts such as arsenic or nitrates.  GAC does not remove microorganisms.

Types of GAC filter systems:

  • Whole–house (POE) 
  • Point-of-Use (POU) 

GAC filters can be installed at the point-of-use (POU) or as a whole house treatment system depending on the contaminant being removed. For example GAC systems are installed to reduce undesirable taste and odors although it may not considered necessary for health reasons.  The GAC filters will also remove other chemicals like tannic acids, residual chlorine and chlorine by-products (THMs).

Whole-house GAC systems installed to treat released VOC or pesticide contaminants must be sized by an experienced professional water treatment dealer based on the level of contamination. Water treatment dealers generally rely on the GAC manufacturers to help determine the appropriate type and amount of GAC to use. The system should consist of at least two large tanks filled with GAC to a depth of at least two feet. The type of GAC used is based on cost and the desired chemicals needing to be removed. The three primary types of GAC are coal-based, coconut hull-based, and wood based.  

A whole-house GAC system is installed in series of at least two tanks and monitored for chemical breakthrough at the end of the first tank. When breakthrough occurs, a tank with new GAC is always installed at the end of the run (closest to consumption) and the older GAC tank re-routed as the first treatment tank.  

GAC Filter Replacement

Prior to installing GAC filters, it is important to know the average water use and the type and concentration of the contaminants.  This will help determine how often the filters will need replaced.  Whether using a POU or POE GAC system the activated carbon only last a certain period of time.  Spent carbon can release previously removed chemicals back into the water.

The GAC provides a nutrient base for microbiological growth and can become breeding grounds for bacteria, including pathogenic bacteria.  If the media is not replaced in a timely manner, the GAC will cease to work and also could release toxins that had previously been removed back into the water.  Steps should be taken to remove any pathogenic bacteria ahead of GAC filtration.

When using GAC, the water should be checked on a regular basis to determine chemical and microbiological breakthroughs.

Additional Resource

For more information about granular activated carbon (GAC) treatment contact the Water Quality Association (WQA). The WQA is the national professional organization for water treatment dealers and has information on treatment of aesthetic water quality issues.

Reverse Osmosis

Reverse osmosis (RO) is a common method for the treatment for household drinking water.  RO systems are typically used to reduce the levels of total dissolved solids and suspended matter. Reverse Osmosis works by forcing water under pressure through a semi-permeable membrane that removes many chemicals at the molecular level. On private water systems reverse osmosis systems are typically used at the tap (under the sink) as a point-of-use treatment device (POU).

RO removes or reduces many chemicals including Arsenic, Aluminum, Barium, Cadmium, Calcium, Chloride, Chromium, Copper, Fluoride, Iron, Lead, Magnesium, Manganese, Mercury, Nitrate, PFAS, Potassium, Radium, Selenium, Silver, Sodium, Sulfate, and Zinc. Many RO units are sold as systems that can also remove many volatile organic chemicals (VOCs) and some pesticides using an additional activated carbon component.

RO membranes a generally made of thin film composite (TFC), cellulose acetate (CA) and cellulose triacetate (CTA). TFC membranes have better durability as well as generally higher rejection rates than CA/CTA membranes. TFC are considered more resistant to bio fouling, high pH and high TDS. CA and CTA membranes have a better ability to tolerate chlorine.

RO units do not typically remove 100 percent of a particular chemical or contaminant but can remove a large percent of some chemicals. The removal efficiency can vary depending on the overall water chemistry and other factors such as water temperature and pressure. Generally RO systems waste about 80 percent of the treated water. For every 10 gallons of water treated 2 gallons are usable and the rest goes down the drain as wastewater. However, consideration has to be given to the variability in the efficiencies different types of RO systems.   

RO is often combined with other treatment methods such as granular activated carbon and /or point of entry ion exchange (water softener) to improve the over-all treatment efficiency

  • Granular Activated Carbon
  • Ion Exchange

Although RO can remove many microorganisms (such as protozoans) it is not considered an acceptable method for the continuous disinfection of private water systems in Ohio.  ROs are not whole-house disinfection devices and have the potential for bio-fouling at the RO treatment membrane. Microbiologically unsafe private water systems need to be treated at the point-of-entry (POE), that is whole house treatment systems.  

See ANSI / NSF Standard 058 for a listing of RO units and their removal capabilities.


RO units that are used for removing nitrates should have a thin film composite membrane (TFC). RO units using TFC membranes can reduce nitrate concentration by 60 to 95 percent. When nitrate levels exceed 30 mg/l RO becomes less effective and other alternative treatment systems should be considered. RO units that use cellulose acetate membranes is not recommended for nitrate removal private water system. For more information see the nitrate treatment fact sheet for additional information.


RO can remove 60 to 90 percent of arsenic from water depending on the valence of the arsenic (As III or As V).  Trivalent arsenic is generally more difficult to remove from drinking water than pentavalent arsenic. Trivalent arsenic can be converted to pentavalent arsenic in the presence of an effective oxidant such as free chlorine. The arsenic in water containing detectable free chlorine or that has been treated with another effective oxidant will be primarily in the pentavalent arsenic form.

If the arsenic valence is unknown, RO may still be used to treat the drinking water at the tap water for arsenic not exceeding 70 ug/l (same as a ppb) with caution. Since arsenic treatment of the water for the trivalent form is estimated to provide 60 percent removal this can reduce the finished water to the US EPA MCL of 10 ug/l for arsenic.

RO is used on some municipal water supplies for desalinization and can have the same application for private water systems to treat high saline (high TDS) water as whole- house treatment system. However, although whole-house RO systems are available, they can be expensive and, in many cases not practical due to the high water use and rejection rate.

Additional Resource

For more information about reverse osmosis (RO) treatment contact the Water Quality Association (WQA). The WQA is the national professional organization for water treatment dealers and has information on treatment of aesthetic water quality issues.

Ion Exchange

Ion Exchange Treatment Whole-house (POE)

Ion exchange is a water treatment method in which unwanted or undesirable contaminants are removed and exchanged for a less objectionable substance of the same ion charge.  Ion exchange is either anion (negatively "-" charged ion) exchange or cation (positively "+" charged ion) exchange.  A typical water softener is one type of ion (anion) exchange treatment which uses a specific resin to reduce water hardness by replacing calcium and magnesium (hardness) with sodium.   Examples for treatment include reduction in inorganic chemicals such as:

Ion exchange resins are typically small (1-2 mm diameter) beads, usually white or yellowish, made from an organic polymer resin.  

Highly developed structure of pores on the surface of which are sites with easily trapped and released ions. The trapping of ions takes place only with simultaneous releasing of other ions; thus the process is called ion exchange.  

There are multiple different types of ion exchange resins that are made to selectively prefer one or several different types of ions.  

There are four main types of ion exchange resins differing in their function groups:

  • strongly acidic (sulfonic acid groups, eg. Sodium polystyrene sulfonate or (polyAMPS))  
  • strongly basic, (trimethylammonium groups, eg. polyAPTAC  
  • weakly acidic (carboxylic acid groups)  
  • weakly basic (amino groups, eg. Polyethylene amine)  

Other uses for specialized treatment include mixed bed resins and specialized resin types. Ion exchange resins are designed to remove specific ions but have preferential affinity to exchange some ion over others. Therefore knowing a more complete water chemistry makeup can help provide information to the water treatment professional on how to best design a system to improve the overall treatment.  

Examples of Selectivity of Ion Exchange Resins (in order of decreasing preference).  Ion Exchange resins do not prefer all ions equally.  

Strong acid cation resins (Sodium form)             Strong base anion resins (Chloride form) 
Cation    Anion
Radium   Uranium Dioxide Carbonate 


Lead   Selenate 
Strontium   Sulfate 
Copper    Hydrogen arsenate 
Calcium    Nitrate 
Zinc    Nitrite 
Iron    Chloride 
Magnesium    Hydrogen Carbonate 
Manganese    Fluoride 

*Note:  The anion exchange resin has a preferential affinity for sulfates over nitrates and also has a preferential affinity for nitrates over arsenic.  


For nitrate treatment, anion exchange is installed for whole-house treatment. They work much the same way a water softener does. Use an anion exchange resin that has a preferential affinity for nitrates to exchange chloride for nitrates. Note that when an anion exchange treatment system is used for nitrate reduction the total combined concentration of nitrates and sulfates in the water must be known. The resins used in nitrate removal systems have a preferential affinity for sulfate. This means that nitrates that have already been removed from the water will be re-released back into the drinking water in favor of sulfates when the resin has reached capacity. Also, in order to ensure the most efficient reduction of nitrates, a water softener should precede the anion exchange system to reduce the potential for fouling the nitrate anion exchange resin. For more information about nitrate treatment see


Arsenic removal can become more complicated depending on the type of arsenic being removed and may require an oxidation step prior to the ion exchange step. For more information about the specifics of arsenic removal from water see the links below.

Additional Resource

For more information about ion exchange treatment contact the Water Quality Association (WQA). The WQA is the national professional organization for water treatment dealers and has information on treatment of aesthetic water quality issues.