A water heater system that includes a first water storage tank plumbed in series with a second water storage tank, and methods for controlling such a water heater system. In some instances, and in response to a water draw, a controller may activate both a first heat source associated with a first water storage tank and a second heat source associated for a second water storage tank. This rapid turn-on control may help reduce a drop in water temperature in the first water storage tank that might otherwise occur. The controller may also increase the setpoint temperature of the first water storage tank and/or the second water storage tank in response to a water draw.