Authors: Amber Wilson, Extension Associate, Management, Housing and Consumer Education, Virginia Tech; Kathleen Parrott, Extension Specialist, Housing; Virginia Tech and Blake Ross, Extension Specialist, Biological Systems Engineering; Virginia Tech
Publication Number 356-478, posted January 2000
Iron and manganese are metallic elements that are found in the earth's crust. These elements usually do not present a health hazard when they are present in the household water supply; however, they can cause nuisance problems, such as staining and objectionable taste. Iron and manganese are similar chemically and, therefore, cause similar problems. Iron is the more common of these two elements and can be found in a water source without the presence of manganese; however, manganese is rarely found alone in a water source.
Iron and manganese cause a variety of different nuisance problems. Iron and manganese can affect the flavor and color of food and water. In fact, they may react with the tannins in tea, coffee, and some alcoholic beverages to produce a black sludge, which will affect both the taste and appearance. Iron will typically cause reddish-brown staining of laundry, porcelain, dishes, utensils, and glassware. Manganese causes a similar problem, resulting in a brownish-black stain. These stains are not removed by soaps and detergents; in fact, using chlorine bleach and alkaline cleaners (such as sodium and carbonate) will intensify the stains.
Furthermore, the presence of iron and manganese in the water supply will lead to build up in pipelines, pressure tanks, water heaters, and water softeners. This buildup is associated with a decrease in the amount and pressure of available water and an increase in the cost of operating water-using appliances. Iron and manganese buildup can become expensive when it results in the replacement or repair of plumbing or water softening equipment.
Yet another problem that is associated with iron and manganese in the water is iron or manganese bacteria. These bacteria do not pose a health threat; however, they do produce a red-brown (iron) or black-brown (manganese) slime in toilet tanks and can clog water systems. Iron bacteria feed on the iron or manganese present in the water and can grow in either light or dark conditions. Iron or manganese bacteria can be controlled through some type of disinfection process such as chlorination.
Fortunately, treatment for iron and manganese can be very effective, but the most important factor in achieving effective treatment is identifying what kind of iron, and how much, is present. Likewise, it is important to determine the hardness of the water, temperature variations, and the water's pH (acidity or alkalinity) level. With that in mind, it is recommended that thorough water analysis be completed before selecting a treatment method. Furthermore, water treatment equipment should be selected and installed in coordination with additional water treatment equipment that may be necessary to address other existing water quality problems. Individuals interested in having their water tested can contact their local health department for a list of state certified water-testing laboratories in their area.
The Environmental Protection Agency has established two categories for drinking water standards: Primary Standards and Secondary Standards. Primary standards are based on health considerations and Secondary Standards are based on taste, odor, color, corrosivity, foaming and staining properties of water. Iron and manganese are classified under the Secondary Standards. The Secondary Maximum Contaminant Level (SMCL) for iron in drinking water is 0.3 milligrams per liter (mg/l), sometimes expressed as 0.3 parts per million (ppm), and .05 mg/l (ppm) for manganese. However, water with less than these amounts of iron and manganese may still cause staining problems.
If the water has excessive iron and/or manganese, one of the following five treatment methods can be used: (1) phosphate compounds; (2) ion exchange water softeners; (3) oxidizing filters; (4) aeration (pressure type) followed by filtration; and (5) chemical oxidation followed by filtration. Except for the phosphate method, these treatment methods are most effective when used in a water supply that has an almost neutral pH (approximately 7.0). All of the methods will remove both iron and manganese. The table outlines appropriate treatment for iron and manganese problems.
| Indication | Cause | Treatment |
|---|---|---|
| Water is clear when drawn but red-brown or black particles appear as combined concentration of iron water stands; red-brown or black stains on fixtures or laundry | Dissolved iron and/or manganese |
|
| Water contains red-brown or black particles when drawn; particles settle out as water stands | Iron particles from corrosion of
pipes and equipment
OR Oxidized iron/manganese due to exposure of water to air prior to tap |
Raise pH with neutralizing filter
OR Particle filter (if quantity of oxidized material is high, use larger filter than inline; e.g., sand filter) |
| Red-brown or black slime appears in toilet tanks or forms clogs in faucets | Iron or manganese bacteria | Kill bacteria masses by shock treatment with chlorine or potassium permanganate, then filter; bacteria may originate in well, so it may require continuous feed of chlorine or potassium permanganate, then filter |
| Reddish or black color that remains longer than 24 hours | Colloidal iron/manganese; organically complexed iron/ manganese | Chemical oxidation with chlorine or potassium permanganate; followed by filtration |
Source: "Drinking Water: Iron and Manganese" (G96-1280-A) Cooperative Extension, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln (1996).
Although phosphate is an inexpensive treatment method for low levels of iron and manganese, it is important to remember that the iron and manganese is not actually removed from the water and the water may still have a metallic taste. Using too much phosphate compound will result in water that will feel slippery. Furthermore, phosphate compounds are not stable at high temperatures, and if the water is heated or boiled, the phosphate compounds will break down and become ineffective. Also important to note is that phosphate compounds do contribute to excess nutrient levels in surface water. Therefore, phosphate treatment is not recommended in areas where phosphate is limited in cleaning products, as in Virginia. Reducing phosphates in surface water is an important concern in Virginia's Chesapeake Bay watershed.
When using this method, the iron in the water is exchanged with sodium, or occasionally potassium, ions. The iron is then flushed from the softener by backwashing (forcing sodium-rich water back through the device) and then the iron is carried away through the wastewater.
Iron removal does reduce the softening capacity of the unit; therefore, it may have to be recharged frequently. Furthermore, not all water softeners are capable of removing iron, so be sure to check the manufacturer's specifications.
Water softeners do add sodium to the water; therefore, if you are concerned about your sodium intake, you should consult with your doctor. Water softeners can be installed to bypass the cold water in the kitchen, allowing untreated water to be available for drinking and cooking.
With this type of treatment system, a small feed pump is used to add the oxidizing chemical to the water supply. The process requires a retention time of at least 20 minutes to ensure that the oxidation takes place. Next the particles must be filtered. If large amounts of iron are present, a flushing sand filter may be needed. Any type of filtration material that is used requires regular backwashing or replacement to eliminate the solid iron/manganese particles.
When organic-complexed or colloidal iron/manganese is present in the water supply, higher concentrations of chemicals and a longer retention time may be required for proper oxidation to take place. It may be helpful to add aluminum sulfate to the water because it improves filtration by causing larger iron/manganese particles to form.
If you use chlorine as the oxidizing agent, it is important to note that any excess chlorine will stay in the water. While chlorine is an effective disinfecting agent, unpleasant taste results from too much chlorine. Using an activated carbon filter is an effective way to remove excess chlorine and improve taste.
The pH of the water supply should be considered when choosing an oxidizing agent. If the pH of the water is less than 6.5, a neutralizing treatment is needed before chemical oxidation. Chlorine bleach is the most effective for oxidizing iron if the pH level is 6.5 to 7.5. Consequently, chlorination is not recommended for treatment of high levels of manganese because a pH level of 9.5 or greater is required for complete manganese oxidation. Potassium permanganate can oxidize manganese at pH levels of 7.5 or higher and is also an effective method of oxidizing organic iron.
However, caution must be exercised with potassium permanganate because it is both a poison and a skin irritant. Furthermore, it is very important that no excess potassium permanganate be present in the water supply. In addition, caution must be exercised when storing the concentrated potassium permanganate to ensure that it is kept where children and animals cannot access it. If potassium permanganate is used, careful calibration, maintenance, and monitoring of your water treatment equipment is necessary.
It is important that the filter be backwashed from time to time to ensure proper performance. Furthermore, aeration is not recommended if the water contains organic complexes of iron/manganese or iron/manganese bacteria that will clog the filter or aspirator.
Consumers are encouraged to talk to a Water Quality Association Certified Water Quality Specialist before purchasing water treatment equipment. Certified Water Quality Specialists are individuals that work in the water quality improvement industry and have passed the Water Quality Association certification examinations. Water Quality Association member dealers can be located by looking under "Water Treatment Companies" in the yellow pages of your telephone directory.
Another helpful tip is to look for the Water Quality Association Gold Seal on the product. This seal assures consumers that the equipment has been tested against industry standards and validated for performance capabilities. Likewise, consumers can look for the NSF, National Sanitation Foundation, certification mark to ensure that they are purchasing quality products. Another helpful tip for consumers is to pay careful attention to the reputation of the manufacturer and warranty offered. Last, consumers can check with the Better Business Bureau for references and complaints.
If further assistance is needed, please contact your local Virginia Cooperative Extension office to obtain a copy of one of the following publications or visit our website at http://www.ext.vt.edu
Varner, D., Skipton, S., Hay, D., & Jasa, P. (1996). Drinking Water: Iron and Manganese. (G96-1280-A) Lincoln, NE: Cooperative Extension, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln.
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