<p>The use of solar water heating (SWH) systems to generate hot water for low-temperature applications contributes significantly to the reduction in the use of fossil fuel-derived energy. Phase change materials (PCMs), which are used to store thermal energy, when incorporated into SWH systems, improve the thermal efficiency. Salt hydrate PCMs have great potential for use in solar water heating systems. However, certain drawbacks, such as supercooling, limit their use. In this study, the performance of an experimental scale SWH system incorporating a modified sodium acetate trihydrate (SAT) PCM has been investigated. The modified SAT PCM was prepared by adding lithium carbonate as a nucleating agent and carboxymethyl cellulose (CMC) as a gelling agent to the SAT. The constructed SWH system was tested for 3 days without the use of PCM and 3 days with the use of PCM. The targeted application temperature range was 45 to 55 °C. From the results, the maximum tank water temperatures of 64.8 °C and 65.3 °C were achieved on the days without PCM and with PCM, respectively. Results indicated that the system with PCM was able to keep the tank water temperature above a minimum operating temperature of 45 °C for 5 h longer than the system without PCM. Also, the average tank water temperature recorded at the end of the experiment was 45.9% higher for the days with PCM. The average storage efficiency of the PCM was 0.843. Average system efficiencies of 0.43 and 0.58 were achieved on the days without PCM and with PCM, respectively. This represents an increase in system efficiency of 34.9% when the PCM was used. The results indicate an improved system performance when the modified SAT PCM was used.</p>