The goal of this study was to improve the performance of a parabolic trough solar water heater (PTSWH) by using a dimpled texture design on the water tube and copper oxide/deionized water (CuO/DI-H2O) as a cell-side nanofluid (NF). Experimental tests will be conducted to measure and validate the thermal performance improvements using the dimpled tube–CuO NF combination. The nanoparticle (NP) concentration in the NF and the water mass flow rate (MFR) through the dimpled tube were varied for experimental and numerical analysis. The PTSWH achieved the highest efficiency of 38.25% with a CuO volume concentration (VC) of 0.3% and a water MFR of 2.5 kg/min, 12% higher than the unembellished tube with base fluid. Furthermore, the PTSWH’s overall output performance index under the same conditions was 3.56. Furthermore, at an MFR of 3.0 kg/min and a VC of 0.5%, the pressure drop was 7.24% greater. For dimple tube (computational fluid dynamics analysis), at an MFR of 3.0 kg/min, the increase in temperature [$\Delta T=({T}_O-{T}_I$)] at CuO NP VC of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% was found to be 54°C, 56°C, 58°C, 60°C, and 62°C, respectively. These findings show that using NF and dimpled tubes to improve the performance of PTSWH systems has a high potential for a more sustainable and efficient use of solar energy.