Today, saving and storing water are among the most critical and important issues which have attracted the world's attention. History of storing water in the form of ghanat and water reservoir by Iranians goes back to ancient times. Studies on this field show that benefiting from underground dams was one of the methods employed for exploiting water in past times. In countries like Iran, due to experiencing noticeable variations in groundwater levels during dry and wet seasons, this method has been considered beneficial for refining and storing water in dry seasons throughout the year. Following field studies and investigation of geological and geoelectrical properties of the region, this article presented the method of positioning the best site for constructing an underground dam and making an underground reservoir. In this paper, Watershed Koohzar Underground dam has been studied.