Iron makes up about five percent of the earth’s crust. It can be a soluble or relatively insoluble form found in water. Soluble iron is found in:
- oxygen-free reservoirs,
- dead-ends in water distribution systems, and
- scale (hard mineral coatings) within pipes.
When soluble iron is exposed to oxygen or to a disinfectant during water treatment, it oxidizes to the relatively insoluble iron. This is responsible for discolored water.
The primary sources of iron in drinking water are from natural geologic sources 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
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 gauge whether different kinds of treatments effectively removed iron from drinking water. Elevated iron levels can cause drinking water to be a rusty color. This can stain laundry or household items. Discolored water is one of the most frequent consumer complaints about drinking water.
- Physical effects are damages to water equipment and reduced effectiveness of water treatment for other contaminants. This may cause additional costs water utilities. Corrosion of distribution system pipes can produce sediment or loose deposits that blockor slow down 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:
- Reducing contaminants in drinking water
- Saving costs by extending the useful life of water mains and service lines
- Saving energy from transporting water more easily through smoother, non-corroded pipes
- Reducing water losses resulting from leaking or broken mains or other plumbing
- Managing the acidity, alkalinity, and other water qualities that affect pipes and equipment used to transport water.
Conventional treatments can be used to remove secondary contaminants, such as iron, from our drinking water. These treatments include:
- aeration, and
- the use of granular activated carbon.
Nonconventional treatments include:
- reverse osmosis, and
However, these are fairly expensive technologies and may be impractical for smaller systems.
Non treatment options include blending water from the principal source with uncontaminated water from an alternative source.
Results and Impact
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. They are used as guidelines to assist public water utilities in managing their drinking water for aesthetic considerations.
State health agencies and public water utilities often 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.