Providing potable water for buildings through a reliable technique using sustainable and renewable energies is crucial for saving fossil fuels. Desalination systems could afford fresh water using solar energy. Nanofluids have been applied in solar stills to enhance their productivity. In this study, an inclined stepped solar still with baffles is fabricated to investigate the effect of CuO/GO nanocomposite wt. %, volume ratio of individual nanoparticles in the nanocomposite, presence of paraffin wax as a phase change material (PCM), and input brine flow rate on the distillate yield, glass, brine and bottom temperatures. The results showed that 0.03 wt % CuO and GO boosted the freshwater yield by 48.12 and 81.59%, respectively. A nanocomposite with volume ratio of 30/70 for CuO/GO increased the volume of the freshwater by 81.59%. Additionally, it has been found that decreasing the brine flow rate from 30 to 8 L h−1 increased the freshwater production and conversely increasing to 68 L h−1 caused reduction of the distillate yield. Finally, application of paraffin wax as PCM under the steps of solar still caused an increase of 32.8% in distillate yield. Generally, it is revealed that the nanocomposite of CuO/GO is a hopeful candidate for application in solar stills to enhance their productivity.