Courses of the basin's water are constituted of the Oum-Er-Rbia oued and its main tributaries: Tessaout, Lakhdar and El Abid. Contributions of water of the Oum Er Rbia basin are valued to 3680 Mm³/yr, variable between a maximum of 8300 Mm³ and a minimum of 1300 Mm³. Numerous sources contribute to those of the snow melting and guarantee a very sustained level for the Oum-Er-Rbia.

The groundwater resources of the Oum Er-Rbia basin are relatively important, distributed between several aquiferous units.

The aquiferous of the Tadla form a multicouche system composed of 4 aquiferous superimposed separated by impervious or semi impervious levels. The four aquiferous of the system are from the stocking toward the top:

• The carbonated Turonien aquiferous; 
• The Senonien aquiferous ; 
• The calcaréo - sandy Eocène aquiferous ; 
• The quaternary alluvionnaireses aquiferous of the Tadla and the Tessaout downstream (aquiferous of Beni Amir, aquiferous of Beni Moussa, aquiferous of the Tessaout downstream).