Iron in drinking water
Iron is one of the earth's most plentiful resources, making up at least five percent of the earth's crust. Rainfall seeping through the soil dissolves iron in the earth's surface and carries it into almost every kind of natural water supply, including well water. Although iron is present in our water, it is seldom found at concentrations greater than 10 milligrams per liter (mg/1) or 10 parts per million (ppm). 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/I (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.
Types of Iron
Iron is generally divided into two main categories:
1) Soluble or
"Clear water" iron, is the most common form and the one that creates the most complaints by water users. This type of iron is identified after you've poured a glass,of cold clear water. If allowed to stand for a few minutes, 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. Although not very common in Wisconsin's water wells, insoluble iron can create serious taste and appearance problems for the water user.
Because iron combines with different naturally occurring acids, it may also exist as an organic complex. A combination of acid and iron, or organic iron, can be found 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. Iron 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 tank when you remove the lid. Actions you can take to correct an iron problem 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, pH, alkalinity, and hardness. 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.
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. Talking to your neighbors about their well depths and iron levels will give you some idea of what well depth would pump 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.
The following list contains treatment considerations for the various forms of iron. For additional information on water treatment systems, contact your County Extension Office or Extension Publications, RM. 245 30 N. Murray street, Madison, WI 53715 and ask for publication G3558-5, "Choosing a Water Treatment Device".
Treatment considerations for various forms of Iron
- 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.
- Water Softener: Removal of soluble iron by ion exchange.
- Manganese Greensand: An ion exchange sand material which is capable of removing iron. 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.
- Ozonation: A specialized form of aeration using ozone to convert soluble 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.
- Chlorination: Chemical oxidizer used to convert soluble iron to an insoluble, filterable form.
Important points to remember if you are considering an iron treatment system
When you choose 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?
- 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).
- Will the treatment unit treat the water at the flow rate required for my water system?
- 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).
- Would well construction or reconstruction be more cost effective than a long term iron removal treatment process?