Electrocoagulation (EC) is an effective process to remove fluoride from water, but few of scientific literatures explore its inside mechanism. A new approach was used in this study to investigate fluoride distribution in the EC defluoridation process, which divided the fluoride into three parts: remained in water, removed by electrodes, and adsorbed on hydroxide aluminum flocs. The fluoride distribution was investigated in terms of several critical parameters such as pH, charge loading, current density and initial fluoride concentration. The experimental results showed that the removal by electrodes was primarily responsible for the high defluoridation efficiency, and the adsorption by hydroxide aluminum flocs gave a secondary effect. The parameters affected the efficiencies of defluoridation in a way of changing the fluoride distribution in the EC process. A chemical complex of Al-n(OH)(m)F-k(3n-m-k) was formulated to explain the mechanism inside the EC defluoridation process. The new approach provides a detailed insight of the electrocondensation effect, which helps to gain more scientific comprehension about the cooperation between electrochemical and chemical ways occurring inside the EC process. (c) 2007 Elsevier B.V. All rights reserved.