Abstract: A water heating apparatus comprising a refrigerant loop for natural circulation which includes a hot water storage tank for holding water to be heated, a heat collecting plate for collecting solar heat, and refrigerant tubes having a refrigerant sealed therein and extending to unite the hot water storage tank with the heat collecting plate and another refrigerant loop for refrigeration cycle which includes a compressor and an expansion valve which are connected in the refrigerant tube uniting the hot water storage tank with the heat collecting plate. The water in the hot water storage tank is elevated in temperature selectively by the natural circulation action where there is a sufficient amount of sunshine or by the refrigeration cycle where the amount of sunshine is insufficient.