This study aims to understand hydrogeochemical functioning of groundwater in Moundou city. This city is located in southwest of Chad between 16° 02’ and 16° 12’ East longitude and 8° 51’ and 8° 60’ North latitude. To carry out this study, 15 water points were sampled (8 wells and 7 boreholes,) from November 21 to 26, 2019; and chemical parameters analyzed are HCO3-, Cl-, NO2-, Na+, K+, Ca2+, Mg2+, SO42-, NO3-. In order to determine origins and processes of mineralization of groundwater hydrochemical and statistical approaches were used. The results show through Chadah diagram, that groundwater presents 2 facies: a bicarbonate calcic and magnesian facies (HCO3-Ca-Mg) and a chloride calcic and magnesian facies (Cl-Ca-Mg). Results also show that main phenomena at origin of mineralization of waters are alteration of silicates, cationic exchanges, evaporation and anthropic activities.