Iron
Cities measured
87
Detected in
87 / 87
EU limit
200 μg/L
Highest
265 μg/L — Beirut
Overview
Iron is the most common heavy metal problem in drinking water — primarily from corrosion of cast iron and steel distribution mains, some over 100 years old in European cities. It causes red-brown water, metallic taste, and staining. Source water iron is generally low in Stockholm.
Health Relevance
Iron is an essential nutrient. At drinking water concentrations (< 0.3 mg/L), it poses no health risk. High iron promotes bacterial biofilm growth in pipes. Iron overload disease (hereditary haemochromatosis) is not caused by water iron at normal concentrations.
Regulatory Limits
Drinking Water Directive 2020/2184
200 μg/L (indicator — aesthetic parameter).
Controversy & Contested Science
Unlined cast iron water mains from the Victorian era underlie European city centres, leaching iron and harbouring complex biofilms. 'Red water events' (iron scale disturbance during pressure changes) are underreported because utilities typically flush mains quietly rather than reporting exceedances formally. The EU Drinking Water Directive requires infrastructure assessment plans, but enforcement is highly uneven. Some Stockholm inner-city mains date to the 1890s–1920s, and full replacement is decades away at current capital investment rates.