The thermal performance of the thermosyphon water heater unit was analyzed to show its applicability in Bahrain, using data of several sunny, cloudy and hazy days in winter. The performance of this unit was studied under various maximum daily solar intensities, ranging from 1, 2 and 3 on a cloudy day, upto 695 W/m(2) on a sunny day, with the daily outside temperature ranges between 25-19 degreesC. The results show that the system has an average efficiency of 38% with storage tank temperature above 50 degreesC. These results show that this system is quite suitable for application in Bahrain weather conditions.