Iron is the most common metal found in the universe, and comprises at least 5% of the earth‘s crust. It stands to reason that some of it will eventually be found in all the waters of earth, including your well water. This is particularly true if you live in the Northeast region where iron is liberally deposited in the granite strata.
Iron in well water typically comes in four different forms, and often more than one is present in a single sample. They can all cause staining, metallic or foul taste, and fouling of pipes and plumbing. This presents a challenge for water conditioning, as different removal methods need to be applied to reduce the iron to acceptable levels.
Ferrous iron, also called clear iron because it is invisibly dissolved in the water, is very common. The slight acidity of rainwater causes the iron to dissolve into solution. If you draw a glass of water containing ferrous iron, the water will appear clear, possibly for a day or more. This iron tends to stain fixtures a reddish brown color as it is exposed to oxygen, or whenever it comes in contact with oxidizing chemicals such as soaps and detergents.
Ferric iron is iron that is already oxidized (rust), and therefore insoluble. A glass of water containing ferric iron will very quickly develop a film of orange on the bottom as the particles settle out of solution. It causes staining of fixtures, laundry and the dishwasher, as well as fouling plumbing. This form is also very common in our region’s groundwater.
The two less common types of iron are Organic iron and Colloidal iron. Each has peculiar characteristics making them challenging to filter.
Organic iron is ferrous iron that has been metabolized by iron bacteria as part of their diet. These organisms form jelly-like deposits of ferric iron, and can be identified by clumps of iron scum in water and an oily sheen on the surface of water, especially in toilet tanks.
Colloidal iron is comprised of extremely fine particles (smaller than 1 micron), which due to their size and electrical charge remain in suspension. A glass containing colloidal iron will have a reddish-pink tinge to it. These iron particles are so tiny they have a low specific gravity practically the same as the water. It can take a very long time for them to finally settle out of solution.
The two most effective methods for removal of ferrous iron are ion exchange (softening), which pulls the iron molecules out of water by electrochemical attraction, and oxidation and filtration. The latter method uses air or a chemical oxidizer to convert the ferrous iron to ferric particles, which can then be mechanically filtered out.
Organic iron is more difficult to remove, as the biological scum mass that encapsulates it tends to shield the iron from traditional removal methods. Wells containing iron bacteria should be disinfected with chlorine to kill the problem at the source, or the incoming water can be treated by a chemical feed system utilizing a strong oxidizer to destroy the biomass and then the residue can be mechanically filtered out. Organic iron is difficult to treat under most circumstances.
Colloidal iron also presents a serious challenge for residential filtration, as the most effective removal involves injecting an adhesive agent such as alum to bind the tiny particles together into large enough clumps to fall out of solution and be mechanically trapped. Fortunately, this problem is quite rare.
If you see the telltale signs of any of these four types of iron in your water, contact a certified water specialist for proper testing and treatment.