The system consists of a flat-plate collector and a storage tank. Flat-plate collector is made of galvanised steel tube and aluminium plate, with MAXORB selective surface, encased in a mild steel tray with top single glass cover, bottom has been provided with glass wool insulation. It is kept facing equator and at lambda + 15degrees tilt (lambda latitude of the place). The double walled storage tank is of 1001 capacity. The inner drum is made of 18 gauge galvanised steel and outer of mild steel. Space (100 mm) between them is filled with glass wool insulation. Performance and testing of solar water heater has been carried out extensively. It has been found that the heater can provide 100 l of hot water at an average temperature of 60.6 degreesC at 16:00 h when tap water temperature was 23.6 degreesC, it can retain hot water till next day morning at an average temperature of 51.6 degreesC. The overall efficiency of the heater is 57%. Based on performance at Jodhpur, a model has been developed by using ambient temperature and solar radiation for the prediction of its performance at various Indian stations. The predicted performance at various Indian stations revealed that hot water is required at most places for domestic use only during winter season and it can provide 100 l of hot water at an average temperature of 50-70 degreesC that can be retained to 40-60 degreesC till next day morning use.