## 1 Introduction  
As the climate changes, many remote regions, especially in the Middle East, are facing a severe shortage of freshwater resources. Iraq, with a population of about 40 million people, will face multiple water challenges, including a severe shortage of drinking water [1, 2, 3]. According to United Nation reports, the water flow of the Tigris and Euphrates rivers will be reduced by more than 25% and 50%, respectively, by 2025. As a result of reducing water flows, the water salinity will increase. To address this issue, many researchers have worked to use renewable energy sources, such as solar distillation technology (solar still), to desalinate salt water [4, 5, 6, 7, 8, 9, 10]. The essential factors influencing the solar still system performance are the solar radiation intensity, type of solar still, design of solar still, sunshine duration, climate conditions, and geographic differences [9, 10, 11, 12, 13, 14]. A detailed experimental investigation of 10 homemade solar stills at glass inclination angles of 10, 15, 20, 25, 30, 35, 40, 45, 50, and 55 degrees under Iraqi climate conditions was performed by [PERSON] et al. [15]. The findings demonstrate that the inclination angles between 30 and 35 have the least water productivity and performance, while the inclination angles between 20 and 25 have the best water productivity and cost-effectiveness. Another experimental investigation concerning the influence of absorber plate surface shape on the stepped solar still thermal performance and water productivity [16]. The obtained data showed that utilising the convex absorber plate resulted in higher average water productivity than using the flat absorber plate. According to [PERSON] et al. [17], the still's energy performance is strongly affected by basin water depth. They experimentally studied the influence of water depth on the energy performance of the pyramid solar still painted with TiO\({}_{2}\) nano black paint under Egyptian climate conditions. They claimed that as the depth of the water decreases, the temperature of the basin water rises, resulting in higher water productivity. Moreover, their results indicated that the best productivity was found at a water depth of 1 cm. [PERSON] et al. [18] experimentally confirmed that varying the water depth in pyramid solar still has a significant influence on energy performance and water productivity. Their results showed that at 1 cm water depth, maximum daily thermal efficiency was 28.50 and 26.17%, while the maximum productivity was 3.72 and 3.27 kg/m\({}^{2}\) with and without insulation, respectively. An experimental investigation was performed by [PERSON] et al. [19] using a pilot-scale solar still with a variable amount of basin water (from 3 to 4) litres and salt concentration (from 2000 to 8000) ppm under the climate conditions of Bangladesh. The results show that the maximum water productivity can be achieved with the optimum basin water amount (3.5) litres at which the water depth is equal to 1.6 cm. Moreover, they found an inverse relationship between water productivity and salt concentration. Based on the above-detailed investigations of literature, it is obvious that the productivity of water from the still is highly dependent on the temperature difference \(\left(T_{w}-T_{gl}\right)\), in which the water depth plays an important role. Although energy evaluation has been studied and analysed intensively, it is only recently that the exergy evaluation has gained significant attention for evaluating the performance of various solar desalination systems. Exergy analysis, which is formulated according to the second. The law of thermodynamics is a perspective approach for the performance evaluation, design, and optimization of desalination systems. [PERSON] et al. [20] conducted a theoretical exergy analysis of simple configuration solar still. They reported that exergy efficiencies of the basin plate, water basin, and the overall system are 12.9%, 6%, and 5%, respectively, for the same input exergy.