Groundwater quality of the arid and semi-arid regions needs great attention because it is the main water exporter for household and irrigation purposes. In this study, the traditional method and the water quality index were applied to evaluate the suitability of groundwater quality for drinking and irrigation purposes in south-western part of Libya. To achieve this, twenty groundwater samples were collected from different places representing the area understudy and the necessary physic-chemical analyzes were carried out to examine the suitability of groundwater for drinking purposes. Eleven parameters (pH, electrical conductivity, total dissolved solids, total hardness, calcium, magnesium, sodium, potassium, chloride, bicarbonate and sulphate) have been applied for calculating the WQI for drinking testes. The obtained values for water quality parameters were compared with World Health Organization (WHO) guideline values (traditional method). Also, seven parameters were selected for irrigation testes for calculating the WQI such as: EC, SSP, SAR, MAR, PI, KR and PS were used in traditional method. The results revealed that the groundwaters of most samples were fit for drinking purposes according to WHO (traditional method). However, the calculated DWQI for drinking propose showed that 35% of water samples are considered of excellent category, 20% good category, 15% poor category and 20% very poor category. On the other hand, two samples (only 10%) are of unsuitable categories. For irrigation purposes, most of studied samples were suitable for irrigation purposes (traditional method). While, the computed IWQI showed that 15% of water samples were in excellent category and 85% were in good category. The graphical interpretation of water quality was made according to Gibbs plots, Piper diagram, Chadha’s scheme, USSL diagrams, Wilcox diagram and Doneen diagram.