Under climate change, the role of water management organisations is becoming critical for mitigating future water scarcity in Arid Regions. During the last couple of decades, many government-managed water allocation schemes were transferred to private organisations such as water users' associations (WUAs). The transfer of the water management authority from the government to WUAs had significant impacts on improving operation and maintenance of irrigation facilities as well as increasing the water fee collection rates. However, recently some WUAs are experiencing difficulties in management because of their small-scale operation sizes. This chapter attempts to address the relative efficiency of WUA management by suggesting an alternative composite efficiency index. We observed the case studies earlier conducted on the WUAs in the Lower Seyhan Irrigation Project in Adana, Turkey. And we applied DEA (data envelopment analysis) to compare the efficiency levels with management-, engineering- and welfare-focused models. The analysis revealed that some WUAs are suffering from unfavourable management practices and there is a scope for major reorganisation. Concerning the future climate change and water scarcity in the region, the role of WUAs for efficient management of water resources seems important.