Abstract: A water heating system includes a solar collector panel, a hot water heater tank, a serpentine tube-in-sheet heat exchanger jacket built into the water tank assembly, pumping means, fluid transfer means and means for securing the heat exchanger jacket around the hot water heater. The solar collector panel has a first passageway which lies beneath the outer surface of the panel such that incident solar energy is used to elevate the temperature of an energy-absorbing fluid which is circulating through this first passageway. The heat exchanger jacket is constructed with second and third passageways which are positioned in a double serpentine coil arrangement. The energy-absorbing fluid from the collector panel flows through connecting conduits to and from the second passageway. Water within the hot water heater is coupled to the third passageway and, as it circulates through the third passageway, this water is elevated in temperature by means of conduction from the energy-absorbing fluid.