The alarming situation of the network of cleansing of the Ouargla town put in the obligation the authorities to create several outlets around the city. However, the rejection of urban effluents without any preliminary treatment is accentuated the enhancement and the contamination of the water table on one hand, and on the other hand, it generated the degradation of the closer palm plantations. This oasis knows today a catastrophic ecological situation, which could be the origin of many epidemics. Facing to cleansing and management of purification stations problems, it's recommended to involve other techniques of purification less expensive and simpler to manage in order to protect the public health and to safeguard the receiving backgrounds. The use of a local material, such as the sand of the dunes, as biological filter is a promising technique for the purification of the water used in the Algerian South. Among many parameters, which condition the purification capacity of those natural techniques, it's included: their physicochemical characteristics, the quality of water to be treated and the speed of filtration. This study made it possible on one hand to determine the physicochemical characteristics of sand's dunes (structure, texture and chemical composition) and to put forward their filtering capacity and on another hand to evaluate the purification performances of the designed prototype.