Abstract: The present invention is a method and system for treating iron-contaminated water (e.g., mine drainage) using an innovative treatment approach identified herein as the Activated Iron Solids (AIS) Process. The AIS process is capable of oxidizing and removing iron as iron oxides from iron-contaminated waters (such as, mining-related discharge, groundwater, surface water and industrial waste streams) producing a clean effluent. The AIS process is performed in a single or multiple tank system in which a catalytic surface chemistry process increases the iron removal 1000s times faster than would naturally occur and 100s of times faster than existing arts (e.g., aerobic pond passive treatment). In addition, the AIS process can utilize inexpensive alkaline material (such as, pulverized limestone) where initial mine drainage alkalinity (mg/L as CaCO3) to ferrous iron (mg/L) ratio is less than approximately 1.7.