Several discharge water outlets with unknown origin appear around Jatiluhur dam body. Same of discharge water was found around the main tower which is located at the center of the dam. This work is conducted to study the origin of discharge waters. In this research, chlor ion, as one of the most conservative tracers in water, has been utilized along with oxygen-18 isotope to identify every suspicious discharge water. To carry out the investigation, the research begins by collecting secondary data dollowed by montly collection of water samples from several sources such as from discharges water, observation wells, rain, and reservoir. After the collection, the samples were brought to Pusat Penelitian dan Pengembangan Teknologi Isotop dan Radiasi-BATAN laboratory to be analyzed for the stable isotope (oxygen-18) and hydro-chemical contens. Two water discharges were successfully identified as leakages from the reservoir that are asenceur and RD located around main tower at the end of the dam gallery. On the other hand, seepage that appear to the right toe of dam (Pohon Asam) and the discharge V-NOTCH just to the left of tailrace are not the leakages from the reservoir.Paston Sidauruk, Alip & Bungkus Pratikno
