Iron occurs naturally in rocks and soil, which easily dissolves in water. Iron is therefore commonly found in well water. While not a health issue, iron gives water a metallic taste and will stain fixtures and clothing. The amount of iron and the nature of its source point to the most effective treatment approach.
One source of iron in well water is iron bacteria. These naturally occurring bacteria live on iron found in water or in plumbing components. The bacteria form a slime layer—called a biofilm—on the inside of pipes and water tanks. It only takes a small amount of iron to support the growth of iron bacteria.
To control iron bacteria, periodically shock the well and plumbing with chlorine. This process is described in Ohioline’s “Shock Chlorination of Wells” AEX-318 (Mancl 2019). Iron bacteria are difficult to kill, as the slime layer offers a level of protection from the chlorine. Also, iron bacteria always grow back, so it will be necessary to shock chlorinate the water system on a regular basis. Check the back of the toilet tank for any slime build-up to help develop a shock chlorination schedule. Treatments may be necessary every six to 24 months. Long periods of no water use will contribute to the slime buildup. Vacation homes or even extra bathrooms that see little use may thus require more frequent treatments.
Iron in Well Water
The other source of iron in wells is iron that has dissolved in the water. Deep in the ground, groundwater has no oxygen. Under these anaerobic conditions, iron in rock, sand or gravel is colorless and easily dissolves. Once the groundwater is pumped to the surface and exposed to air, small, rusty, red particles slowly form. This change from clear, dissolved iron to red iron particles is called oxidation and is the same process that occurs when iron or steel starts to rust.
The amount of iron dissolved in water helps determine the most effective type of treatment. A small amount of colorless iron can be sequestered with polyphosphate or removed with a water softener. But once the iron has turned red, or if it is a large amount, separate iron removal filters should be used.
If a water test reveals a small amount of iron has dissolved in water, it can be captured before it has a chance to oxidize and turn red. One way to achieve this is by adding polyphosphate to the water. Polyphosphate surrounds the iron and sequesters it, so it cannot oxidize and turn red. Phosphates are sometimes added to detergents to sequester minerals that interfere with cleaning. Phosphate feeders can inject a small amount of this sequestering agent into the water, tying up the iron so it cannot oxide into red particles.
Another way to capture small amounts of colorless iron is by using a water softener. In this process, dissolved, colorless iron is exchanged for sodium in the same way hardness minerals are exchanged. When using a water softener to remove small amounts of iron, special “iron-out” salt should be used to regenerate the softener and protect it from iron buildup.
Iron (greensand) Filter
For larger amounts of iron, or iron that has turned red, an iron filter is recommended. Iron filters do two things—first, a chemical is used to quickly oxidize the iron to particles, and then, the particles are filtered out. An iron filter is often called a greensand filter and is designed to do the two steps in one tank (Figure 1; Wagenet, Mancl and Sailus 1995; page 55). The greensand is first treated with a dark purple solution of potassium permanganate. Potassium permanganate is a strong oxidizing agent, that will quickly turn dissolved iron into large, feathery, black particles that are easily trapped in the filter. To maintain the system, the filter is backwashed to remove the particles, then more potassium permanganate is added.
Potassium permanganate is a corrosive chemical, so care must be taken when handling it. Wear gloves, goggles, and an apron to protect clothing when refilling the feed tank. Also, thoroughly wash the iron particles out of the filter to ensure proper filter operation. Each filter has minimum backwash requirements of flow rate and water pressure. If your water system has a low flow rate, consider using an iron filter cleaning service. A water company will bring in a clean, recharged iron filter on a pre-determined schedule and take away the used one. Backwashing and recharging with potassium permanganate are done in a shop with adequate water and chemical-handling equipment.
Chlorine Followed by Filtration
For high levels of iron, a two-tank system is recommended. In the first tank, chlorine—a strong oxidizing agent—is mixed with the water to form red iron particles. It takes 20 to 30 minutes for the iron particles to form, so the tank must be large enough to hold on to the water before it goes out for use in the home. The second tank is filled with filter sand that traps the iron particles. The filter has minimum backwash requirements of flow rate and water pressure. Thoroughly washing the iron particles out of the filter ensures proper filter operation.
A chlorine bleach solution is pumped into the first tank to form the iron particles. Chlorine is a corrosive chemical, so care must be taken when handling it. Wear gloves, goggles, and an apron to protect clothing when refilling tanks.
Iron Removal Systems
|Treatment for best results
|Iron concentration in water
|Less than 2 mg/l
|Less than 5 mg/l
|Iron (greensand) filter
|Less than 10 mg/l
|Chlorine followed by filtration
|More than 10 mg/l
Remember, iron in water is not a health hazard, but makes the water unpleasant to use. Be sure to test the water at an independent lab before shopping for treatment equipment. To find a testing lab, see Ohioline’s AEX-315 “Where to Have Your Water Tested” (Mancl and Bradbury 2021).
Iron in Drinking Water
Iron can be a troublesome chemical in water supplies. Making up at least 5 percent of the earth’s crust, iron is one of the earth’s most plentiful resources. Rainwater as it infiltrates the soil and underlying geologic formations dissolves iron, causing it to seep into aquifers that serve as sources of groundwater for wells. Although present in drinking water, iron is seldom found at concentrations greater than 10 milligrams per liter (mg/L) or 10 parts per million. However, as little as 0.3 mg/l can cause water to turn a reddish brown color.
Iron is mainly present in water in two forms: either the soluble ferrous iron or the insoluble ferric iron. Water containing ferrous iron is clear and colorless because the iron is completely dissolved. When exposed to air in the pressure tank or atmosphere, the water turns cloudy and a reddish brown substance begins to form. This sediment is the oxidized or ferric form of iron that will not dissolve in water.
Iron is not hazardous to health, but it is considered a secondary or aesthetic contaminant. Essential for good health, iron helps transport oxygen in the blood. Most tap water in the United States supplies approximately 5 percent of the dietary requirement for iron.
Taste and Food
Dissolved ferrous iron gives water a disagreeable metallic taste. When the iron combines with tea, coffee and other beverages, it produces an inky, black appearance and a harsh, unacceptable taste. Vegetables cooked in water containing excessive iron turn dark and look unappealing.
Stains and Deposits
Concentrations of iron as low as 0.3 mg/L will leave reddish brown stains on fixtures, tableware and laundry that are very hard to remove. When these deposits break loose from water piping, rusty water will flow through the faucet.
When iron exists along with certain kinds of bacteria, a smelly biofilm can form. To survive, the bacteria use the iron, leaving behind a reddish brown or yellow slime that can clog plumbing and cause an offensive odor. This slime or sludge is noticeable in the toilet tank when the lid is removed. The organisms occur naturally in shallow soils and groundwater, and they may be introduced into a well or water system when it is constructed or repaired.
Organic Iron and Tannins
Iron can combine with different naturally-occurring organic acids or tannins. Organic iron occurs when iron combines with an organic acid. Water with this type of iron is usually yellow or brown, but may be colorless. As natural organics produced by vegetation, tannins can stain water a tea color. In coffee or tea, tannins produce a brown color and react with iron to form a black residue. Organic iron and tannins are more frequently found in shallow wells, or wells under the influence of surface water.
Test Your Water
If there is an iron problem with the water supply, the first step is to determine the source. The source of iron may be from the corrosion of iron or steel pipes or other components of the plumbing system where the acidity of the water, measured as pH, is below 6.5.
A laboratory analysis of water to determine the extent of the iron problem and possible treatment solutions should begin with tests for iron concentration, iron bacteria, pH, alkalinity, and hardness. A water sample kit can be obtained from a certified laboratory. The laboratory’s instructions for collecting the water sample should be followed. Collect the sample as close to the well as possible.
If the source of water is a public water system and you experience iron-related problems, it is important to contact a utility official to determine whether the red water is from the public system or from the home’s plumbing or piping.
One alternative in solving an iron problem may be to construct a new water well, eliminating the need for treatment. Depending on local land conditions, it is sometimes possible to extend a “well casing” or “screen” deeper into the groundwater and avoid the water with high iron levels. An Illinois licensed water well contractor, knowledgeable about the quality of groundwater, can be contacted to discuss options.
Below are the treatment methods for the various forms of iron. Before choosing a water treatment method or device, make sure you have answers to the following five questions:
- What form of iron do I have in my water system?
- According to the water test results, will the water treatment unit remove the total iron concentration? (Total iron includes both soluble and insoluble iron.)
- Will the treatment unit treat the water at the flow rate required for my water system?
- Based on the results of the water tests, will this method effectively remove iron? For example, will the pH have to be adjusted prior to a particular treatment?
- Would the construction of a new well or the reconstruction of an existing well be more cost effective than a long-term iron removal treatment process?
Treatment Methods for Various Forms of Iron
|FORM OF IRON
|Tap water is first clear and colorless. After standing, reddish brown particles appear and settle to bottom of glass.
|Dissolved ferrous iron
|Hardness must be calculated and increased sodium concentration should be checked if users(s) on restricted sodium diet. System must be airtight.
|Use of chlorine liquid or pellets. Requires frequent monitoring and proper water pressure. May require lengthy contact time.
|Dissolved oxygen, alkalinity, organic matter, chlorination, polyphosphate, and temperature limitations
|Sequestering (adding chemical agents to water to keep iron to an insoluble, filterable form)
|Method may not prevent staining and may require removal of sequestering agents and iron. Test for agents before choosing another treatment device.
|Tap water appears rusty or has a red or yellow color. After standing, particles settle to bottom.
|Insoluble red water ferric iron
|Dissolved oxygen, alkalinity, organic matter, chlorination, polyphosphate, and temperature limitations
|Use of chlorine liquid or pellets. Requires frequent monitoring and proper water pressure.
|Water tank, toilet tank and plumbing have reddish brown or yellow gelatinous slime or sludge present. Odor may be objectionable.
|Shock chlorination; consider following with continuous chlorination.
|Chlorine products must be suitable for drinking water. Method requires long contact time for adequate treatment.
|Water containing organic iron is usually yellow or brown color, but may be colorless. Tannins stain water a tea color.
|Organic iron and tannins
|First, treat for organics (activated carbon). Check for corrosive properties. System must be airtight.
|First, treat for organics. Maintain adequate pressure.
- Manganese Greensand: A naturally occurring mineral or manufactured material, treated with potassium permanganate that is capable of removing iron; it absorbs dissolved iron and requires chemical regeneration.
- Catalytic Filtration: A granular filter medium that enhances the reaction between oxygen and iron and then filters the insoluble iron.
- Since organic iron and tannins can slow or prevent iron oxidation, water softeners, aeration systems, and iron filters may not work satisfactorily. One option may be chemical oxidation followed by filtration.
Iron is one of the earth’s most plentiful resources, making up at least five percent of the earth’s crust. When rainfall seeps through the soil, the iron in the earth’s surface dissolves, causing it to go into almost every natural water supply, including well water.
When iron is present in our water, it is usually found at concentrations less than 10 milligrams per liter (mg/l) or parts per million (ppm); however, levels high enough to cause problems are often found.
Iron In Drinking Water Types of Iron
Iron is generally divided into two main categories:
1) soluble or ferrous iron and
2) insoluble or ferric iron. Soluble iron, or “clear water” iron, is the type of iron found in our groundwater and oxidizes to insoluble or red iron in the presence of oxygen either in the well or in your home. This type of iron is identified after you’ve poured a glass of cold clear water. If allowed to stand in the presence of air, reddish brown particles will appear in the glass and eventually settle to the bottom.
When insoluble iron, or “red water” iron is poured into a glass, it appears rusty or has a red or yellow color. Insoluble iron can create serious taste and appearance problems for the water user. Iron, which combines with different naturally occurring organic acids or tannins, may also exist as an organic complex. A combination of acid and iron, or organic iron, can be found anywhere; however, it is more common in shallow wells and surface water.
Although this kind of iron can be colorless, it is usually yellow or brown. Finally, when iron exists along with certain kinds of bacteria, problems can become even worse. The bacteria consume iron to survive and leave a reddish brown or yellow slime that can clog plumbing and cause an offensive odor.
You may notice this slime or sludge in your toilet bowl or tank when you remove the lid. For more information on iron bacteria, find the DNR publication, Iron Bacteria Problems in Wells at dnr.wi.gov. Search: Iron Bacteria.
Once you determine whether you have “clear water,” “red water,” “organic” or “bacterial” iron in your water, you can take steps to correct the problem. Keep in mind that no one treatment method will work for every type of iron problem.
Test Your Water Before you attempt to remove anything that appears to be iron-related, it is important to have your water tested. A complete water test to determine the extent of your iron problem and possible treatment solutions should include tests for iron concentration, iron bacteria, manganese, pH, alkalinity, and hardness.
Check the business pages of the phone book under “Laboratories-Testing” to find a water testing lab or call a licensed professional for assistance.
Certified laboratories can also be found at dnr.wi.gov. Search: Lab Lists. If you receive your water from a public water system and experience red water problems, it is important to contact a utility official to determine whether the red water is from the public system or your home’s plumbing or piping. Well Construction/Reconstruction High iron levels may be avoided in some cases by changing the screen or casing depth of the well as long as the minimum casing depth requirements are still met. Talking to your neighbors about their well depths and iron levels will give you some idea of what well depth would provide the lowest amount of iron. It is also helpful to talk to a well driller or pump installer about local conditions and the cost of drilling a new well in your area.
The cost of well work should be compared to the long term (perhaps twenty years) cost of treating the water for any iron related problems. Treatment Table 1 lists treatment considerations for the various forms of iron.
For additional information on water treatment systems, contact your County Extension Office or Extension Publications, and ask for publication G3558-5, Choosing a Water Treatment Device or you could contact a licensed plumber. A list of water treatment devices approved for use in Wisconsin can be found by typing “Wisconsin Approved Treatment Devices” in your search engine.
When choosing a water treatment method or device, make sure you have answers to the following five questions:
1. What form of iron do I have in my water system?
2. Will the water treatment unit remove the total iron concentration (determined by the water test) in my water supply? (Total iron refers to both soluble and insoluble iron combined).
3. Will the treatment unit treat the water at the flow rate required for my water system?
4. Considering the results of my water test, will this method effectively remove iron? (For example, pH may need to be adjusted before beginning a particular treatment).
5. Would well construction or reconstruction be more cost effective than a long term iron removal treatment process?
Health and Water Quality Iron is not considered hazardous to health. In fact, iron is essential for good health because it transports oxygen in your blood. In the United States, most tap water probably supplies less than 5 percent of the dietary requirement for iron. Under Department of Natural Resources (DNR) rules, iron is considered a secondary or “aesthetic” contaminant.
The present recommended limit for iron in water, 0.3 mg/l (ppm), is based on taste and appearance rather than on any detrimental health effect. Private water supplies are not subject to the rules, but the guidelines can be used to evaluate water quality.
For instance, when the level of iron in water exceeds the 0.3 mg/l limit, we experience red, brown, or yellow staining of laundry, glassware, dishes, and household fixtures such as bathtubs and sinks. The water may also have a metallic taste and an offensive odor. Water system piping and fixtures can also become restricted or clogged.
Iron Treatment Terms Aeration:
Introducing oxygen to the water source to convert soluble iron to its insoluble form. Filtration: Media used to entrap and screen out oxidized particles of iron. Usually requires backwashing to remove accumulated iron.
Removal of soluble iron by ion exchange. Manganese Greensand: An ion exchange sand material which is capable of removing iron and manganese. Adsorbs dissolved iron and requires chemical regeneration. Catalytic Filtration “BIRM”: A granular filter medium that enhances the reaction between oxygen and iron and then filters the insoluble iron.
A specialized form of oxidation using ozone to convert soluble iron to insoluble iron. Ion Exchange: Substituting an acceptable ion (such as sodium) for soluble iron. Sequestering: Adding chemical agents to water to keep metals like iron in solution to prevent characteristic red stains.
Chemical oxidizer used to convert soluble iron to an insoluble, filterable form. The Wisconsin Department of Natural Resources provides equal opportunity in its employment, programs, services and functions under an Affirmative Action Plan.
If you have any questions, please write to:
Equal Opportunity Office, Department of the Interior, Washington, D.C. 20240. This publication is available in alternative format (large print, Braille, audiotape, etc.) upon request.
Please call (608) 266-1054 for more information.
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Additional Information Remember, the type of water you have will determine what type of treatment is possible. No one treatment technique works for every iron problem and well construction or reconstruction may be more cost effective. For additional information on iron in drinking water, contact a water treatment dealer, a licensed plumber or a licensed well driller or pump installer. For information on other water quality concerns go to dnr.wi.gov. Search: What’s wrong with my water
. Table 1: Treatment Considerations for Various Forms of Iron Characteristic Known As Treatment Methods Considerations Drawn tap water is clear and colorless. When allowed to stand, reddish brown particles appear and settle to bottom. Soluble Clear Water Fe+2 Ferrous Dissolved Aeration/Filtration May require lengthy contact time. Temperature dependent.
Water softener Hardness must be calculated. System must be airtight. All water must be treated. Chlorination/Filtration. Chlorine liquid or pellets. Frequent monitoring. Proper water pressure. Manganese greensand/ Filtration Requires adequate pressure.
Catalytic filtration “BIRM” Dissolved oxygen, organic matter, chlorination, polyphosphate, temperature limitations Ozonation Used by some municipal systems in conjunction with infiltration. May be expensive. Sequestering. May not prevent staining. May need to remove sequestering agents and iron. Test for agents before choosing another treatment device. Drawn tap water appears rusty or has a red or yellow color. When allowed to stand, particles settle to bottom. Insoluble Red Water Fe+3 Ferric Oxidized Manganese greensand/ Filtration Requires adequate pressure.
Catalytic filtration “BIRM” Dissolved oxygen, alkalinity, organic matter, chlorination, polyphosphate, temperature limitations Chlorination/Filtration Chlorine liquid or pellets.
Frequent monitoring. Proper water pressure. Water tank/toilet tank/ plumbing have reddish brown or yellow gelatinous slime or sludge present. May have objectionable odor or oily sheen. Bacterial Crenothrix Leptothrix Gallionella Shock chlorination and consider following with continuous chlorination. Bactericides. Shock chlorination should include: cleaning the well thoroughly, cleaning pump and riser pipe, and complete chlorination and flushing of distribution system. Make sure bactericides can be used in drinking water. Bactericides need long contact time for adequate treatment. High color content (yellow or brown) or colorless. Generally groundwater from shallow well or surface water. Organic Hemme Tannin Water softener First step is to treat for organics. Hardness must be calculated. System must be airtight. Treat all water. Manganese greensand/ Filtration First step is to treat for organics. Requires adequate pressure. Ozonation Used by some municipal systems in conjunction with infiltration. May be expensive.
This brochure was revised by the Wisconsin Department of Natural Resources with assistance from the Education Subcommittee of the Groundwater Coordinating Council.