A tub (50) for a humidifier configured to humidify a flow of breathable gas, the tub being configured to hold a supply of water, the tub comprising: an inlet (120) to receive the flow of breathable gas an outlet (122) to deliver the humidified flow of breathable gas and a water level detection means comprising a first conductive portion (ink 44) and configured to indicate a water level of the supply of water based on determination of electrical conductivity between the first conductive portion and the supply of water.
