Methods of an apparatus determine a quantity of a body of water in a humidifier such as by indirect measurement. The quantity of water may be determined by measuring one or more properties or characteristics, from which the quantity of water may be inferred. Characteristics of a flow of air, the humidifier, and/or the body of water may be measured. The characteristics may be, for example, pressure, flow rate, noise, vibration, temperature, electrical or mechanical. These may be measured by one or more sensors, which may be located in the humidifier, RPT device, air circuit or the patient interface. The methods described may have advantages, for example in being able to detect the quantity of water without requiring sensors to be present in a disposable component, and in some cases, without introduction of additional sensors.一種諸如藉由間接測量以決定一增濕器的水主體量之裝置。該水量可藉由測量一或多個特性或特徵而決定，從該等特性或特徵可推測水量。空氣流、該增濕器、及/或該水主體的特徵為可測量。該等特徵可為(例如)壓力、流率、噪音、震動、溫度、電氣或機械。這些可藉由一或多個感測器測量，該等感測器可設置在該增濕器、呼吸壓治療(RPT)器件、空氣通道、或患者介面。該等所述方法可具有效益，例如，無需在一次使用性組件內設置感測器；且在某些情況，無需使用額外的感測器便可偵測水量。
