The invention relates to the field of water heaters, in particular to a water heater water tank with a laterally-arranged automatic control water feeding device. The water tank comprises a water tank outer shell and an inner container arranged in the outer shell, a water inlet pipe is arranged on the side wall of the inner container, a water stopping valve is arranged on the water inlet pipe, and the water stopping valve is connected with a switch device for controlling the water stopping valve to be opened and closed. The switch device comprises a power source, a transmission component and a floating ball control component, the power source provides power through elastic force of itself, the transmission component transmits power to control the water stopping valve to be opened and closed, and the floating ball control component controls the power source and the transmission component to be connected and disconnected. When a floating ball is arranged at the position filled with water/the water supplementing position, the floating ball control component controls the power source and the transmission component to be disconnected/connected, and therefore the opening and closing states of the water stopping valve are controlled, and the functions of automatically stopping the water feeding process when the water heater is filled with water, and the function of automatically feeding the water are achieved. The floating ball is arranged on the side portion of the water tank to automatically control the water feeding device, and the use corrosion and aging conditions caused by the fact that the water stopping valve is soaked in the water for a long time are avoided.