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The Tillabery Region in West Africa (Sahel Region) is affected by a severe semi-desert climate. After the rainy season, ponds and the majority of watercourses dry up. Population has to exploit superficial alluvial aquifers using traditional methods. The most important aspect in groundwater supply is its quality. Since 2004, Niger government has been developing a project to provide each village with a source of drinking water. Until now, over 500 boreholes have been made for underground water supply. Thirty-eight boreholes were selected for the groundwater quality assessment (G-WQ(i)), each characterized by 15 different physico-chemical parameters: water temperature, pH, nitrites, nitrates, electrical conductivity, chlorides, sulphates, calcium, magnesium, potassium, fluoride, sodium, bicarbonates, dissolved iron and total manganese. The statistical analysis indicates 7 parameters that do not comply with the standards for drinking-water quality (after World Health Organization): nitrites, nitrates, electrical conductivity, carbonate hardness, sodium concentration, dissolved iron and total manganese. This concentration may have severe implications for human health and can lead to spreading of diseases. According to the G-WQi score, 10 samples belong to the "Good water quality" class, 16 samples belong to the "Medium high water quality" class, 10 samples belong to the "Medium low water quality" class, and 2 samples correspond to the "Poor water quality" class. The results of this study can be useful for a proper managagement of water resources in the Sahel Region.