Algeria is among the semi-arid or even arid countries that suffer from drought, where precipitation does not exceed 400 mm/year and water resources are scarce, irregular and located in the coastal strip. In the Algerian Sahara, non-renewable groundwater resources estimated at 5 billion m3 thus constitute the indispensable support for irrigation. This is especially the case since agricultural development programs, aimed at integrating the Sahara into the national economy, have based on an agri-food model implemented outside existing oases through the conquest of new agricultural land and the use of pumped groundwater. In the Berriane region in the north of Ghardaïa region (center of Algerian Sahara), an agricultural perimeter called Oued El Bir (300 ha in total) was officially created in 2013 downstream a wastewater treatment plant. Farmers had informally settled in the area, already a wastewater discharge site, since 2009 and had practiced unofficial irrigation with raw wastewater, a “frontier settlement” that proves the high value placed on this resource. As part of Massire project financed by IFAD (2018-2024), the objective of our study was to analyze the water reuse practices in this Berriane arid region, i.e. to study the importance of the institutional management of the treated wastewater reuse on the one hand. And on the other hand to show that the malfunctioning of the wastewater treatment plants can lead to many constraints such as the infiltration of raw sewage into the groundwater, illicit untreated wastewater irrigation and a slowdown in the development of the agricultural perimeter. Our research methodology is founded firstly on interviews with all stakeholders (about 20 surveys with farmers and local institutions) and secondly on isotopic, chemical and biological water analyses that will be carried out soon to validate the hypothesis of infiltration of wastewater into the aquifer. In addition, to overcome of the institutional resistance, we also built with local stakeholders a water reuse demonstrator in a regional eco-neighborhood. The decentralized treatment process is based on a sceptic tank and a fixed bacterial filter (Advanced Enviro Septic) with 10 m3/day capacity. The treated wastewaters are used to irrigate a 1 ha surface of new oasis area. As part of our study, we are investigating the sanitary and agronomic safety of this new treatment process for water reuse in the arid context.