Limestone has been widely used in the treatment of acidic water due to its capability of neutralizing acidic conditions and removing metals in water. This book provides an insight into the application of a limestone-based reactor i.e. a laboratory-scale anoxic limestone drain for treating acidic water. The anoxic limestone drain was basically designed to enhance limestone dissolution and alkalinity generation thus minimizing the potential of armouring which may decrease the rate of acid neutralization. Actual raw water which is highly acidic was used to assess the performance of such system.