Appearance supersedes health as the motivation for a newly released Canadian guideline for the acceptable level of iron in drinking water. The threshold of less than 0.1 milligram, or 100 micrograms, per litre is categorized as an “aesthetic objective” to help boost consumer confidence in the quality of water that municipal utilities provide.

Background from Health Canada’s Safe Environments Directorate reiterates that iron is unlikely to cause health effects unless more than 45 milligrams per day are ingested. Drinking water typically accounts for less than 10 per cent of most consumers’ total daily iron intake.

Nevertheless, iron oxides in water can cause discolouration and a metallic taste. At higher concentrations, there is some concern that the by-products of iron corrosion can undermine the effectiveness of disinfectants used to treat the water supply. Meanwhile, processes to remove iron often have wider health benefits since they can also reduce concentrations of other minerals, such as manganese.

Municipal water utilities rely on various technologies, including aeration, chemical oxidation, coagulation in tandem with granular or membrane filtration, adsorption or biological filtration. “Most well-operated and optimized treatment plants can achieve iron concentrations of 0.1 mg/L or less in the treated water,” the government advisory states.

The guideline was subject to a 60-day public consultation in 2023 and the final version reflects feedback from that process.