ONE of the most challenges to increase water resources use ……...efficiency and sustainability in arid and semiarid regions is the reuse of drainage water. The objective of this study was to assess the quality of drainage water in Siwa oasis and to address the suitability of its reuse to serve the sustainable management of water resources in the oasis. Georeferenced drainage water samples were collected in triplicates from 182 drains distributed around the oasis having different categories indicated by their depths ranging from 0.5 to 2.65 m. Measurements of pH, EC and analyses for soluble Na⁺, Ca²⁺, Mg²⁺ and Cl^- ions and NO₃-N were conducted then SAR and RSC were calculated. Volumes of drainage water were calculated using measured wetted length, width and depth of the sampled drains segments. Descriptive statistics, frequency distribution and Piper tri-linear analyses were performed on the obtained data. The calculated volume weighted averages of pH_avg, EC_avg, SAR_avg, RSC_avg, and NO₃-N_avg were 8.85 dS/m, 7.46, 21.19, 1.72 and 13.51 mg/l, respectively. These averages were found to be generally higher than their calculated mathematical mean values. This represents C3S4 class of salinity and sodicity hazards and nitrate has not any impact on the environment. Application of the Piper tri-linear diagram for the hydrochemical facies indicated that drainage water is Na-Cl-SO₄ type. For such an isolated oasis, regulation of groundwater pumping, lining irrigation canals and improvement of drainage networks, application of modern irrigation systems, the adoption of a suitable IFDM system and increasing the public awareness of the water crisis were suggested by the author.