Abstract: The scarcity of freshwater at coral reefs and islands receives more and more attentions. The precipitation on the coral islands and reefs is one of the major freshwater source. The freshwater lenses formed by the natural precipitation is relatively thin and take a long time to recharge.  This paper presents a laboratory study of desalination of seawater under an electrical field. The precipitation process was simulated by the distilled water. Three electrical fields were used in the study; 0.833C/cm, 1.667V/cm and 2.500 V/cm. Three precipitation intensities were also set; .0303ml/min/cm², 0.0455ml/min/cm² and 0.0606ml/min/cm². The results indicate that, under the electrical field, the degree of desalination is higher than that of under the natural conditions. The highest desalination was found under an electrical field of 1.667V/cm and a rainfall intensity of 0.0606 ml/min/cm². Compared with ears near the cathode, higher degree of desalination was found at areas near anode. When the voltage gradient is 2.5V/cm and the rain intensity is 0.0606ml/min/cm², the intermediate point has the strongest desalination capacity.

Key words: Coral Reefs and Islands, Voltage Gradient, Intensity of Precipitation, Degree of Desalination, Desalination Capacity