Iron

Iron makes up about five percent of the earth’s crust and can exist as soluble ferrous iron or as the relatively insoluble ferric form found in water. Soluble ferrous iron is found in ground water, in anaerobic reservoirs, in dead-ends in water distribution systems, and in scale (hard mineral coatings) within pipes. When soluble ferrous iron is exposed to oxygen or to a disinfectant during water treatment, it oxidizes to the relatively insoluble iron (i.e., suspended colloidal and particulate iron) that is responsible for discolored water.

The primary sources of iron in drinking water are natural geologic sources as well as aging and corroding distribution systems and household pipes. Iron-based materials, such as cast iron and galvanized steel, have been widely used in our water distribution systems and household plumbing.

Effects of Iron on Human Health, Water Quality, and Distribution System Infrastructure
Iron is an essential mineral for human health in small concentrations (iron deficiency can lead to anemia). Unlike lead and copper, ingesting iron from drinking water is not directly associated with adverse health effects; although, trace impurities and microorganisms that are absorbed by iron solids may pose health concerns.

The effects associated with iron contamination can be grouped into two categories:

Aesthetic effects are undesirable tastes or odors. Iron in quantities greater than 0.3 milligrams per liter (mg/L) in drinking water can cause an unpleasant metallic taste and rusty color. Taste is a useful indicator of water quality even though taste-free water is not necessarily safe to drink. Taste is also an indicator of the effectiveness of different kinds of treatments that effectively remove iron from drinking water, such as water softening or reverse osmosis treatment systems. Elevated levels of iron in drinking water can also cause a rusty color that can stain laundry or household. Discolored water is one of the most frequent consumer complaints about drinking water.

Physical effects are damages to water equipment and reduced effectiveness of treatment for other contaminants that may present added costs to operations for water utilities. Corrosivity and staining related to corrosion not only affect the aesthetic quality of water, but may also result in distribution system problems. Among other things, corrosion of distribution system pipes can produce sediment or loose deposits that block water flow.

Corrosion and Metal Solubility Control

Control of corrosion and metal solubility is perhaps the single most cost-effective method for preventing iron contamination. Significant benefits include:

• Reduction of contaminants at our taps
• Cost savings by extending the useful life of water mains and service lines
• Energy savings from transporting water more easily through smoother, non-corroded pipes
• Reduced water losses resulting from leaking or broken mains or other plumbing

Corrosion control is used to manage the acidity, alkalinity, and other water qualities that affect pipes and equipment used to transport water. By controlling these factors, the chance of iron leaching into our water supply is reduced.

Conventional treatments can also be used to remove secondary contaminants, such as iron, from our drinking water. These treatments include coagulation/flocculation, filtration, aeration, and the use of granular activated carbon. Nonconventional treatments include distillation, reverse osmosis, and electrodialysis. However, these are fairly expensive technologies and may be impractical for smaller systems. Nontreatment options include blending water from the principal source with uncontaminated water from an alternative source.

Regulations

Unlike lead and copper, the ingestion of iron in drinking water is not directly associated with adverse health effects, so mandatory iron regulations are not in place. However, based on aesthetic issues, EPA has issued a Secondary Maximum Contaminant Level (SMCL) of 0.3 mg/L for source water iron. (Note: EPA does not enforce SMCLs; rather, they are used as guidelines to assist public water utilities in managing their drinking water for aesthetic considerations.)

Although federal regulations do not require them to do so, state health agencies and public water utilities often decide to monitor and treat their supplies for secondary contaminants; for example, source water iron can be removed by oxidation, followed by sedimentation and filtration or by iron sequestration (that is, using any mechanism to prevent visible precipitation).

Technical Contact:

Darren Lytle (513) 569-7432
Michael Schock (513) 569-7412

See Also:

Safe Drinking Water Act

List of Drinking Water Contaminants and MCLs