This research studied about hidrologie modeling for water availability analysis using the GR4J (Ge'nie Rural a` 4 parame`tres Journalier) method of the Rokan River Basin (DAS). The GR4J model uses data input in the form of daily rain data on Rambah Utama station and daily potential evapotranspiration data, climatological data on Rambah Utama station. The result of this modeling was tested using…