A water heater system includes a water tank and a flow-through heating assembly. The water tank contains heated water. The flow-through heating assembly may extend into the water tank and heats water as water is passed through an interior channel of the flow-through heating assembly. In one embodiment, the flow through heater assembly is a thermosiphonic heater having a hollow body and a heating element extending therein such that an annular recess is defined between an interior surface of the hollow body and the external surface of the heating element.