The availability of hot water for residential application is of great importance for the health and comfort of the residential occupants. In Iraq specially in the recent years after 2003 year there is a big problem in the production and supply of electric power because of several reasons. This means problems and difficulties in operating the electric water heating systems which are high power consuming systems. There are also problems and difficulties with operating gas or kerosene air and water heating devices for residential applications, which push to more dependence on electric power for these applications. The present work suggests the use of a solar water heating system to reduce the consumption of electric power for water heating component. The suggested water heating system to be used in this research is a flat-plate solar water heating system. A computer program is written by the author to predict the long term performance of the system under study by calculating the solar fraction of the studied system using the f-chart method. The annual performance prediction of the selected system in Iraq is based on the meteorological data for three main Iraqi cities and the standard technical parameters of flat-plate solar water heating systems.