Using an advanced Brillouin sensing system (BOTDA) with high spatial resolution, this paper demonstrates the application of the distributed temperature fiber optic sensor (FOS) in small liquid leak detection in soil. The effectiveness and efficiency of the distributed Brillouin sensor in detecting and locating drop leakage in soil is qualitatively verified through a laboratory experiment. Numerical studies based on finite element (FE) method are conducted to simulate the whole drop leak process. The good agreement of the data measured in the experiment and the computational results validates the spatial distribution and the variation trend of the soil temperature field due to drop leakage. A quantitative relation between the active area of the leak-induced temperature field and the FOS measurements is established to determine the size of leak or to propose a FOS-based strategy for leak early warning. (C) 2016 Elsevier Ltd. All rights reserved.