There are many solar water heating systems with different processes and different applications used around the world. After many researches and many investments that were made in the solar water heating system and after the effective results that these systems, it makes the solar heating a promising renewable energy source. The aim of this project is to design a double coil storage tank that well help to heat the water and save the temperature inside the tank. Where water will first pump to the solar collectors to absorb heat. Then it this water will go to the storage tank and circulates in the coil of allowing the transferring of heat from the water inside the coil to the water in the storage tank. The storage tank is designed to have double coil system one for the solar energy and the other for the boiler as a backup system. This system is under testing and design were done for the coils of the tank.