The water resources in the Ahaggar region are extremely limited, with the alluvial terraces intersected by wadis being the sole source of water. Despite considerable fracturing, the bedrock composed of eruptive and metamorphic rocks is unsuitable for the development of significant aquifers due to its unfavorable hydrodynamic characteristics. The hydrographic network and hydrogeology of the region are determined by major faults, some of which create impermeable boundaries due to their siliceous filling, while others accommodate wadis and facilitate the formation of alluvial aquifers. These alluvial aquifers are recharged by the wadi floods that occur during the summer “monsoon” in the Sahel region. The isotopic content and the levels of radioactive Carbon and Tritium in the water of the alluvial aquifer are similar to current precipitation, indicating a recently formed water table. In contrast, the isotopic, radioactive Carbon, and Tritium compositions of water from the bedrock reveal an older origin during a more humid and colder period.