A water heater (1, 2) comprising: a heating part including a burner configured to cause a combustion reaction from air and a fuel, and configured to generate heating water by using heat generated through the combustion reaction; and a humidification part (40, 40b) configured to generate steam by steaming water by using a combustion gas generated through the combustion reaction and discharged from the heating part, and to provide the steam, together with the air, to the burner, wherein an outlet of the humidification part (40, 40b), from which the air and the steam, which are to be provided to the burner, are discharged, is formed to face a lower side of the humidification part (40, 40b), and wherein the water heater (1, 2) further comprises: a burner air supply pipeline connecting the outlet of the humidification part (40, 40b) and the burner; and a siphon part connected to a lower side of the burner air supply pipeline at an inlet of the burner air supply pipeline on a downstream side of the outlet of the humidification part (40, 40b) with respect to a flow direction of the air and the steam, while having a "U"-shaped part such that the water, which is collected, is discharged due to a siphon phenomenon when a volume of the collected water becomes a specific volume or more while the water that flows down from the burner air supply pipeline is collected to define a trap. a heating part including a burner configured to cause a combustion reaction from air and a fuel, and configured to generate heating water by using heat generated through the combustion reaction; and a humidification part (40, 40b) configured to generate steam by steaming water by using a combustion gas generated through the combustion reaction and discharged from the heating part, and to provide the steam, together with the air, to the burner, wherein an outlet of the humidification part (40, 40b), from which the air and the steam, which are to be provided to the burner, are discharged, is formed to face a lower side of the humidification part (40, 40b), and wherein the water heater (1, 2) further comprises: a burner air supply pipeline connecting the outlet of the humidification part (40, 40b) and the burner; and a siphon part connected to a lower side of the burner air supply pipeline at an inlet of the burner air supply pipeline on a downstream side of the outlet of the humidification part (40, 40b) with respect to a flow direction of the air and the steam, while having a "U"-shaped part such that the water, which is collected, is discharged due to a siphon phenomenon when a volume of the collected water becomes a specific volume or more while the water that flows down from the burner air supply pipeline is collected to define a trap. a burner air supply pipeline connecting the outlet of the humidification part (40, 40b) and the burner; and a siphon part connected to a lower side of the burner air supply pipeline at an inlet of the burner air supply pipeline on a downstream side of the outlet of the humidification part (40, 40b) with respect to a flow direction of the air and the steam, while having a "U"-shaped part such that the water, which is collected, is discharged due to a siphon phenomenon when a volume of the collected water becomes a specific volume or more while the water that flows down from the burner air supply pipeline is collected to define a trap.