Method of detecting liquid in a sterilization system

A method is provided for detecting moisture in a sterilization chamber or other enclosure (including moisture present on the external or lumened surfaces of an instrument or other load placed in the enclosure). The method includes the steps of exhausting air from the enclosure under vacuum until the pressure in the enclosure is reduced from a starting pressure to a predetermined subatmospheric pressure which is above the saturation pressure of water, and then a second predetermined subatmospheric pressure which is below the saturation pressure of water or other liquid. The times taken to reach each pressure from the starting pressure are measured and their difference is calculated and compared to a reference time difference pre-established for a dry system (or, alternatively, in a known, leak-free system, only the pull-down time period to reach the second subatmospheric pressure is measured and compared to a pre-recorded reference pull-down time for a dry system).