In Tunisia, and in most semi-arid countries, problems related to water access by populations are very frequent, especially when irregular rainfall and arid climate combine with the insufficiency of natural water resources, as well as possible anthropic pollution. The city of Gafsa (southwestern Tunisia), is relatively highly populated due to its economic activity. In addition, Gafsa has always been threatened by water scarcity generated by the increasing rate of urbanization, and thus there is growing need for drinking water, agriculture and industry. This has led to an overexploitation of groundwater by around 132% and provoked not only the reduction of water availability but also the deterioration of water quality. Proper understanding of the hydrochemical characteristics of groundwater is important for sustainable development of water resources in this region. For this purpose, a sampling campaign was carried out in aquifers of Gafsa to measure major dissolved ions (Ca, Mg, Na, SO4 and Cl), pH and salinity in order to evaluate the origin of groundwater chemistry and the main mineralization processes occurring in this aquifer system. Obtained data showed high concentrations of the following elements: SO42- (1156.63 mg/l), Cl−(911.34 mg/l), Na+ (645.40 mg/l) and Ca++(384.66 mg/l). Other elements show low contents in the analysed waters which are: Mg2+ and K+, salinity ranging from 0.96 to 15.03g /l for all analysed waters. The pH values oscillate between 7.24 and 8.29. Groundwaters seem to have acquired their mineralization from two sources. The first one has a natural origin principally by the dissolution of halite, gypsum and/or anhydrite, as well as by the dissolution of dolomite. The second one has an anthropogenic origin, probably from fertilizers–pesticides and discharge of domestic and industrial wastewater directly into the aquifers by septic pits. The acquired mineralization seems to play a principal role in the degradation of quality of aquifers in the town of Gafsa.