Understanding water in the Sahara.
Before digging, we study. Why is there water beneath one of the world's most arid deserts? Where does it come from, and why is some water salty? Three explainers on the hydrogeology that makes our wells possible.
Why is there water beneath the Sahara?
The Sahara receives less than 100 mm of rain per year today, yet conceals one of the planet's largest aquifers — the result of over 3.5 billion years of geological history. Palaeozoic sandstones form vast regional reservoirs, and much of this water is "fossil": it infiltrated tens of thousands of years ago, during the humid periods of the "green Sahara". This is why the teams of Les Puits du Désert and NGO Tidène carry out a full hydrogeological study before every borehole — to determine depth, flow rate and water quality.
The aquifers of the Tim Mersoï basin
The Tim Mersoï basin, covering roughly 115,000 km² between the Aïr massif and the Algerian border, holds remarkably rich aquifers. It combines deep fossil aquifers (the Tarat and Guézouman aquifers), a memory of the Sahara's ancient humid climates, and shallower aquifers still recharged by rare rains. It is the main water source for Saharan populations and the mining towns of Arlit and Akokan. A strategic but pressured resource (the cone of depression around Arlit) and vulnerable to pollution, it requires sustainable management — one of the challenges addressed by NGO Tidène and Les Puits du Désert.
Why is some groundwater salty?
Beneath the Sahara, some groundwater is fresh while other water is brackish or salty. This salinity comes from the dissolution of minerals (halite, gypsum, limestone…) that the water crosses during its long underground journey: the longer it stays, the more mineralised it becomes. This is why two neighbouring boreholes can yield very different water. To guarantee drinking water, Les Puits du Désert and NGO Tidène carry out physico-chemical analyses after every borehole, to check that the water meets consumption standards.
See where the water flows today
This science comes to life in the field: explore the wells funded by Les Puits du Désert in the Agadez region on the interactive map.