The presence of iron in drinking water is a common concern for homeowners, primarily due to the metallic taste and the reddish-brown staining it leaves on fixtures and laundry. This iron, typically dissolved from the earth’s crust into groundwater, is a non-volatile mineral that poses a unique challenge to standard home purification methods. Many people turn to boiling as a simple solution for making water safer. Understanding the science of dissolved solids is necessary to determine the best approach for dealing with this persistent water quality issue.
The Science of Iron in Water and Why Boiling Fails
Iron in water exists mainly in two forms: soluble (ferrous) and insoluble (ferric). Ferrous iron is the clear-water type, completely dissolved and invisible until the water is exposed to oxygen, which causes it to convert to the insoluble ferric form. Ferric iron is already oxidized and appears as reddish-brown particles or sediment directly from the tap, causing the distinct staining problems.
Boiling water is a process of evaporation; the water molecules turn into steam and escape, leaving behind any substances that do not evaporate at that temperature. Iron, as a heavy, non-volatile dissolved solid, remains in the water even at boiling point. Furthermore, as the pure water evaporates, the concentration of the remaining dissolved minerals, including iron, actually increases in the reduced volume of water left in the pot.
The high heat of boiling does cause the dissolved ferrous iron to oxidize into the insoluble ferric iron, which can then be seen as rust-colored particles. However, this oxidation only changes the iron from a dissolved state to a suspended particle; it does not remove the iron from the water itself. To remove these newly formed particles, a separate filtration step is required after the water has cooled.
What Boiling Does and Does Not Remove
The primary benefit of boiling water is disinfection, as the high temperature is highly effective at killing pathogens. Boiling water for a few minutes is a reliable method for destroying harmful bacteria, viruses, and protozoa that can cause waterborne illnesses.
Boiling can also remove some volatile chemical compounds, such as chlorine, which easily turn into gas at low temperatures. However, boiling is ineffective against most heavy metals and inorganic minerals, including lead, arsenic, and nitrates, which have boiling points far exceeding that of water.
In some cases, boiling can cause temporary hardness minerals, like calcium carbonate, to precipitate out of the water, forming limescale on the heating vessel. This precipitation is a chemical reaction that reduces the concentration of these specific minerals. Iron, however, does not behave in the same way, and its removal requires a different, dedicated treatment process.
Practical Strategies for Removing Iron from Water
Effective iron removal requires methods specifically designed to handle dissolved minerals. The first step is to test the water to determine the concentration of iron and whether it is in the soluble ferrous state or the insoluble ferric state, as the treatment method depends on the form.
Water Softeners
For water containing low to moderate levels of soluble ferrous iron (typically less than 7 parts per million, or ppm), a standard water softener system can be effective. These systems use an ion exchange process where the iron ions are physically swapped for non-staining sodium ions as the water passes through a resin bed. However, higher iron levels can quickly foul the resin, necessitating more frequent and specialized regeneration cycles.
Oxidation and Filtration
Oxidation and filtration is the most common and versatile treatment for moderate to high iron concentrations. This process works by deliberately converting the clear, soluble ferrous iron into the insoluble, particulate ferric iron so it can be filtered out. Aeration, which simply exposes the water to oxygen, can be used for lower concentrations, but chemical oxidizers are often required for higher levels.
Common chemical oxidizers include chlorine (sodium hypochlorite), ozone, or hydrogen peroxide, which are injected into the water before it flows through a filter tank. Specialized filter media, such as manganese greensand or Birm, are also used. These materials are coated with an oxidizing agent that converts the iron on contact and then physically filters the resulting particles. The filter then periodically backwashes to flush the trapped iron particles out of the system and down the drain.