Abstract: This study shows the design and experimental analysis of flow inside the collector of a natural circulation solar water heater. The water heater was constructed and tested at Ado-Ekiti, Nigeria on Latitude 7.5�N. The results show that the system performance depends very much on both the flow rate through the collector and the incident solar radiation. A typical day analysis of the system shows that collector efficiency is high especially around mid-day when the solar collector receives the highest energy. During the test, the results showed that the system exhibited optimum flow rate of 0.1 kg s.m² at a maximum collector efficiency of 68.5%. Also, the average daily efficiency of the system was 57.7% and the maximum water temperature obtained was 83.5�C, while the maximum ambient temperature obtained was 34.5�C.