Glenda M. Herman, Extension Housing Specialist
Published by: North Carolina Cooperative Extension Service
Publication Number: HE-394
Last Electronic Revision: March 1996 (JWM)
Iron and manganese are minerals found in drinking water supplies. These minerals will not harm you, but they may cause reddish-brown or black stains on clothes or household fixtures. Under guidelines for public water supplies set by the Environmental Protection Agency (EPA), iron and manganese are considered secondary contaminants. Secondary standards apply to substances in water that cause offensive taste, odor, color, corrosion, foaming, or staining but have no direct affect on health. The standard Secondary Maximum Contaminant Level (SMCL) for iron is 0.3 milligrams per liter (mg/L or ppm) and 0.05 mg/L for manganese. Private water supplies are not subject to federal standards, but these standards can be used as guidelines to evaluate the quality of water from wells or springs.
The four forms of iron and manganese commonly found in drinking water are ferrous, ferric, organic and iron bacteria. Normally, water appears clear when first drawn from the cold water faucet. If yours is not, it may contain ferric iron or organic iron. Both color the water. Ferric iron precipitates or settles out. Organic iron does not settle out. In well water, insoluble iron oxide is converted to a soluble form of ferrous (dissolved) iron. Ferrous iron is colorless, but when in contact with air, it oxidizes readily, creating reddish- brown, solid particles that then settle out as ferric oxide. Manganese is similar to iron but forms a brownish-black precipitate and stains. Manganese is less commonly found in groundwater than iron, rarely found alone in a water source, and generally found with dissolved iron.
The presence of iron and manganese in water is not considered health problem. In fact, small concentrations are essential to human health. However, high concentrations of iron may give the water an unpleasant metallic taste while still being safe to drink When iron combines with tea, coffee, and alcoholic beverages, it produces an unappetizing inky, black appearance and a harsh, offensive taste. Vegetables cooked in iron-contaminated water turn dark and look unappetizing.
Iron bacteria (a harmless bacteria), occur in soil, groundwater, and some surface waters. Iron bacteria are considered harmless to health, however, they may give water an off taste or color, cause splotchy yellow stains on laundry, and clog water systems. Iron bacteria usually appear as stringy, slimy, mucous-like substances suspended in fresh water and may be colored brown, red, or white. They thrive on iron in the sink or metal parts of the water system and are most easily seen on the inside surface of the toilet tank.
A water analysis should be done to determine the source of the iron and manganese. Iron and manganese may be present in the water supply or be caused by corroding pipes (iron or steel). Iron from pipe corrosion indicates low pH that may need to be corrected.
A water treatment equipment company or testing laboratory can test water for dissolved or oxidized iron or manganese. Call the North Carolina Cooperative Extension Service center in your county or the public health office for names of laboratories that perform tests for colloidal or organic-complexed iron and manganese.
Ask the testing laboratory how to collect a water sample for an iron and manganese test. Generally, you should take the sample from the faucet closest to the pump. Allow the water to run for 5-10 minutes before sampling to obtain fresh water that has not been exposed to air. Do not sample water that has gone through a water heater or a water treatment unit such as a softener. If the water is clear when first drawn, but red or black particles appear after the water settles, dissolved iron and manganese are present. If the water has a red tint but no particles settle out after a time, colloidal iron is the cause. Reddish brown or black brown slimy masses inside the toilet tank indicate iron or manganese bacteria. Laboratory tests are recommended in all cases to determine iron and manganese concentrations.
Iron and manganese treatment should be based on a chemical analysis of the water showing the type and concentration present. There are five treatment methods for the removal of iron and manganese from home water systems.
A water softener can remove small amounts of ferrous iron and manganese. Iron and manganese in untreated water are flushed from the softener medium (ion exchange) by backwashing (forcing sodium-rich water back through the unit). This process adds sodium to the resin medium, and iron and manganese are carried away in waste water.
The amount of iron and manganese a softener can remove depends on the water properties, the types of regeneration and backwash controls, and the ion exchange resin or zeolite used. You must maintain a clean resin bed by frequent and thorough backwashing and regeneration. Manufacturer literature should be carefully studied and system set-up and operation instructions followed. Caution: Water softeners treat hard water by adding sodium to the water, a health concern for people on sodium-restricted diets. For this reason, you may want to connect a softener only to the hot water line leaving cold, unsoftened water for cooking and drinking. In iron and manganese removal, the softener must treat both hot and cold water since sinks, laundry, and dishwashing equipment are affected. A separate tap can be installed to provide unsoftened water for cooking and drinking.
Dissolved iron and manganese are easily oxidized to a solid form by mixing with air. A pressure aerator mixes air with the water, the air is vented, and then the solid particles are filtered from the water.
This method adds no chemicals to the water and is most effective in warm climates. The filter must be backwashed frequently to properly maintain the system. To protect the water from contamination by bacteria in the air, the system should be totally enclosed and only biologically safe water should be used. The appropriate pumping capacity must be maintained for adequate air intake.
When the total combined iron and manganese concentration is less than 15 mg/l, an oxidizing filter (natural manganese greensand, manufactured silica gel zeolite coated with manganese dioxide, plastic resin beads, or pumicite), is recommended. Some filters are coated with a manganese oxide and are regenerated by using a potassium permanganate solution. An oxidizing filter supplies oxygen to convert ferrous iron into a solid form which can be filtered out of the water.
Frequent backwashing and stirring of a manganese greensand bed helps prevent an iron-fouled bed. After several weeks of use, the greensand filter should be backwashed with potassium permanganate to remove solid particles and regenerate (recoat) the greensand to allow absorbtion of more dissolved minerals. Synthetic filters, such as zeolite, requires less backwash water and softens the water as it removes the iron and manganese.
When the iron and manganese content of the water is extremely high (above 10 ppm), a combination of chemical treatment and filtration is necessary. Small chemical pumps are used to add chlorine bleach, potassium permanganate, or hydrogen peroxide into the water. After a retention time of at least 20 minutes to allow for oxidation of ferrous iron into the insoluble ferric form, the solid particles are filtered out.
When chlorine is used, the treated water can have an unpleasant taste if a particle filter of calcite, sand, anthrocite, or aluminum silicate is used. Use an activated carbon filter to remove both excess chlorine and solid iron and manganese particles. Backwash frequently. Some units have an automatic backwash cycle.
Complexation is a simple and low cost method for removing iron and manganese up to 3 mg/L. A phosphate compound is added to the water to complex (tie up) the dissolved iron or manganese. However, adding phosphates to water supplies is not allowed by law in North Carolina.
If organic-complexed or colloidal iron/ manganese is present in the untreated water, a longer contact time and higher levels of chemical are necessary for the oxidation reaction to take place. Aluminum sulfate (alum) eases filtration by causing larger iron/manganese particles to form.
A multistage treatment operation may be necessary if your water has high levels of iron and manganese and they are in both the dissolved and solid forms. For example, the water could first be aerated, than chlorinated to oxidize residual iron and kill iron bacteria, and then filtered through a mechanical device to remove particles. This can be followed by activated carbon filtration to remove excess chlorine and a water-softener for hardness control as well as removal of any residual dissolved iron and manganese.
Symptom Cause Treatment Water clear when drawn, Dissolved iron or Water softener (less than 5 mg/L of reddish-brown or black particles manganese. iron) appear as water stands; reddish- Aeration (less than 25 mg/L of iron). brown or black stains on fixtures Oxidation/Filtration (less than 15 or laundry. mg/L of iron plus manganese). Chlorination-Filtration (greater than 10 mg/L of iron). Water contains reddish-brown Iron particles from Raise pH with neutralizing filter that particles when drawn; particles corrosion of pipes also filters particles. settle out as water stands. and equipment. Water contains reddish-brown Oxidized iron, Particle filter (if quantity of oxidized or black particles when drawn; manganese, or both material is high, use larger filter than particles settle out as water due to exposure of in line, e.g. sand filter). stands. water to air prior to tap. Reddish-brown or black slime Iron bacteria. Kill bacteria masses by shock treatment appears in toilet tank or from Manganese bacteria. with chlorine or potassium faucet. permanganate, then filter; may re- quire continuous feed of chlorine or potassium permanganate, then filter. Reddish or black color that Colloidal iron, Chemical oxidation with chlorine or remains after 24 hours. manganese, or both. potassium permanganate. Organic-complexed iron, manganese, or both.
Iron and manganese are common household water contaminants with no known direct health effects at levels found in water. Their presence may cause staining and offensive tastes and odors. Treatment of these secondary contaminants depends on the form in which they occur, and the levels of concentration. Iron and manganese removal, bacteria control, water softening and treatment for any other contamination may be separate problems, yet they must be considered together. Accurate testing is important prior to selection of a treatment system. The table above may help you identify and determine treatment(s) for iron and manganese in household water supplies.
Kolega, John J. Water Conditioning and Treatment of Iron and Manganese. Fact Sheet 9. University of Connecticut Cooperative Extension Service. 1989.
Machmeier, Roger E. Iron in Drinking Water. University of Minnesota Agricultural Extension Service. 1971.
Plowman, Faye T. Iron and Manganese. Fact Sheet 5. University of New Hampshire Cooperative Extension Service. 1989.
Wagnet, Linda and Ann Lemley. Iron and Manganese in Household Water. Fact Sheet 6. Cornell Cooperative Extension. 1989.
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