A water heating apparatus comprises: an exhaust gas passage through which an exhaust gas from a burner flows; a connecting pipe through which water flows; a first heat exchanger configured to exchange heat between sensible heat contained in the exhaust gas and water flowing through a heat exchanger tube, and arranged at upstream side of the exhaust gas passage and downstream side of the connecting pipe; a second heat exchanger configured to exchange heat between latent heat contained in the exhaust gas and water flowing through a heat exchanger tube, and arranged downstream of the exhaust gas passage and upstream of the connecting pipe, wherein the connecting pipe is provided for supplying water heated by the second heat exchanger to the first heat exchanger; a water supply pipe for supplying water to the second heat exchanger; a water drain pipe being connected to the connecting pipe at an intermediate portion between the second heat exchanger and the first heat exchanger, and a bypass pipe being connected between the connecting pipe and the water supply pipe in such a position as to bypass the second heat exchanger and designed to allow a at least predetermined minimum amount of water required for a burner combustion operation to flow therethrough into the first heat exchanger, characterized in that the bypass pipe is connected to the connecting pipe through the water drain pipe, that is between the water supply pipe at the upstream side of the second heat exchanger and the water drain pipe, in an up-and-down direction, such that water does not remain in the bypass pipe after drainage of water from the water drain pipe. an exhaust gas passage through which an exhaust gas from a burner flows; a connecting pipe through which water flows; a first heat exchanger configured to exchange heat between sensible heat contained in the exhaust gas and water flowing through a heat exchanger tube, and arranged at upstream side of the exhaust gas passage and downstream side of the connecting pipe; a second heat exchanger configured to exchange heat between latent heat contained in the exhaust gas and water flowing through a heat exchanger tube, and arranged downstream of the exhaust gas passage and upstream of the connecting pipe, wherein the connecting pipe is provided for supplying water heated by the second heat exchanger to the first heat exchanger; a water supply pipe for supplying water to the second heat exchanger; a water drain pipe being connected to the connecting pipe at an intermediate portion between the second heat exchanger and the first heat exchanger, and a bypass pipe being connected between the connecting pipe and the water supply pipe in such a position as to bypass the second heat exchanger and designed to allow a at least predetermined minimum amount of water required for a burner combustion operation to flow therethrough into the first heat exchanger, characterized in that the bypass pipe is connected to the connecting pipe through the water drain pipe, that is between the water supply pipe at the upstream side of the second heat exchanger and the water drain pipe, in an up-and-down direction, such that water does not remain in the bypass pipe after drainage of water from the water drain pipe.