Abstract: The identification of different sources of water in a karst groundwater system can not only explain the system's structure, but also help interpret the reason for hydrography and hydrochemistry variations. Quantitative interpretation of the frequency distribution of specific electrical conductivity (SEC) in a spring based on time series data has the capability of identifying water sources within the system. Lingshui Spring, which is in a covered karst basin, was used as a case study to collect conductance frequency distribution (CFDs) over four hydrologic years. The hidden peaks of CFDs were identified and analyzed to determine the water component represented by each peak, then proportion of each kind of water source was calculated. Four kinds of water components were found in Lingshui Spring. The first one is water stored in matrix or fissures in the system, which accounts for 53%-77% of the total discharge. The second one is a water source carrying contaminants from the area surrounding the outlet, which accounts for 3%-7%. The third one is diffusion seepage water through the mantled karst layer or water stored in conduits and fissures with poor mobility pushed out of the aquifer during heavy rains, which accounts for 13%-42%. The fourth one is surface runoff around the lake or water falling directly into lake during raining events, which accounts for 2%-3% of the total discharge. Two typical karst water systems in the peak cluster depression area were compared with Lingshui Spring, and the meanings of the CFDs were analyzed, indicating that the results of CFDs quantifying were in accordance with traditional hydrogeological ways. The study result provides reference for further classifying the 3 620 karst water systems in South China. It is suggested that quantitative interpretation of SEC should be applied and popularized in karst groundwater research in order to know the structure of the system easily and quickly.