A liquid level detecting system which utilizes audio frequency with components having sizes and values usually associated with RF frequencies, thereby providing the reliability and low cost of audio components with the small size typically associated with RF systems. A conductive element is mounted within a container, the conductive element is provided with an insulative coating. A large change in capacitance and capacitance reactance is produced when the insulated conductive element is immersed in a conductive liquid. The change in output of the audio oscillator, passed through the low pass network, which includes the capacitance of the conductive element is fed to an active detector. In one application, the detector is utilized to sense the level of water in a fuel/water separator and, in a second application, a pair of liquid level detectors are utilized to control the operation of a bilge pump.