A tub is configured to contain a supply of water and is configured to be inserted into a chamber of a humidifier. The tub includes a tub base configured to contain the supply of water. The tub also includes a tub lid and a flow plate provided between the tub base and the tub lid. The flow plate includes a water level indicator configured to indicate a level of the supply of water in the tub base. In addition, the water level indicator includes a generally rectangular portion and a generally triangular portion.