A water energy conversion system includes a control unit, a first gas-water energy conversion device, a second gas-water energy conversion device, a water supply device, a storage tank and a heat source unit. Water for different purposes is supplied by the water supply device that collects and transmits various kinds of water resources. Operations of the storage tank as well as the first and second gas-water energy conversion devices are based on water as the basis and a carrier of energy conversion to provide effective energy conversion and recycling. By further employing the heat source unit, high-efficiency cooling, heat dissipation or heat absorption can be achieved with minimal power and water consumption. Thus, the water energy conversion system is applicable for energy conversion, energy regulation and supply for air of indoors and outdoors of a building to realize effects of water storage and supply, anti-flooding, and energy saving and storage.