Solar water heaters are the most popular and economical water heating system that is used in domestic as well as in industrial sector. The design of solar water heater varies with the local meteorological conditions. The design parameters such as number of tubes, number of covers etc should be carefully selected to obtain the maximum efficiency of the solar water heater. The aim of the present study is to develop the simulation tool to evaluate the performance of the solar water heater considering the local weather parameters. A simulation of solar water heater with flat plate solar collector is developed and presented. A computer program consist of independent different subroutines that is capable to handling the variation of spacing between tubes, diameter of the tube, ambient condition, number of cover, thermal properties of the solar collector. Simulation analysis is based on detailed mathematical model that is based on established theory of flat plat solar collector, heat loss from the collector, absorption of radiation, and temperature distribution on the plate.