The municipal water storage system in Caracas consists of concrete tanks located in different zones in the city. In the last few years, leakage problems at some of the city's tanks have surfaced. These case studies highlight the successful application of a GPR technique to locate and detect the most probable zones of water leakage from two such tanks, the La Guarita and the Mariperez tanks. The first study showed that then were defects in the structure of the tanks, which created water leakage. The second study showed that the tank did not present leakage problems, but its integrity and function were being affected by humidity and hydrostatic pressure of soil water, from other sources, in its surroundings.