Identifying the Iron

by Scott Harmon


The presence of iron is often evidenced by staining on plumbing fixtures or its visibility in the water. At other times, it is hidden.

You may need to do some investigating to correctly identify the type of iron present in order to treat it properly.

Ferrous (FE++)

Ferrous or dissolved iron—known as the "invisible" culprit—is the most common. When water containing ferrous iron is drawn from the tap, it will appear clear because the iron is still in a dissolved state.

Once the water is open to the atmosphere or exposed to oxidation the iron will begin to precipitate into ferric iron and the water will become golden to orange in color.

Ferric (FE+++)

Ferric iron, also known as ferric hydroxide or oxidized iron, is iron that has already been converted into an insoluble state and will appear as orange sediment. Once iron is converted to this state it can be filtered out using various types of filter media.

It is important to remember that water containing ferric iron quite often contains some ferrous iron, depending on the level of dissolved oxygen in the water.

Bacterial iron

Bacterial or "live" iron is probably the most misdiagnosed of all iron applications. Unlike ferrous or ferric iron that can be diagnosed by the color of the water, bacterial iron is not readily apparent. It may appear as a feathery or lumpy sediment if visible, and if not properly treated will grow inside the treatment vessels fouling the mineral and causing staining.

Bacterial iron test kits are available and their use is highly recommended. Proper testing will ensure dealers do not misdiagnose the application.

Generally, only chlorination or a redox media is effective with this type of iron. Other types of pre-oxidation can increase the problem and clog the plumbing or filter.

Colloidal iron

Colloidal iron is iron that is comprised of very fine insoluble particles that color the water but will not settle and are almost impossible to filter without flocculation.

This article appeared as a sidebar to a longer article on iron removal. Go here for the full article.


Scott Harmon CWS V, CI is manager of technical support for the RainSoft division of Aquion Partners L.P, Elk Grove Village, IL. Harmon started in the water treatment industry as an installer and service technician, and was the service manager for a local RainSoft dealer before joining Aquion as international service trainer.

By the same author on our site:

The Basics of Iron Removal

The Importance of Backwash Rate

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