Abstract: The freshwater lens below the coral reefs and island is a very important fresh water source, however, not many researches on this aspect are reported. The conventional classification borderline for the saline water is using the 600 mg/L chloride concentration. Due to the uniqueness of the freshwater lens underneath the coral reefs and islands, the conventional groundwater quality and seawater quality standards could not provide enough references for the theoretical study and practical applications. It is recognized that the single chloride concentration classification is unable to meet the investigation and evaluation of water quality for these freshwater lenses. This paper presents a new classification by clustering algorithm, which classifies each water sample by calculating the distance from each data point to the cluster center. The results show that the classification results using SpCond, ORP and Turbidity are satisfactory.

Key words: coral reefs and islands, freshwater lenses, groundwater classification, Kmeans