A unique Liquid Carry Over Sensor (LCOS) is being developed as part of the condensing heat exchanger and filter assembly (CHXFA). The CHXFA is used in the Environmental Control and Life Support System (ECLSS) of the Columbus Orbital Facility (COF), the European Module of the International Space Station (ISS).The LCOS is designed to monitor the performance of the condensing heat exchanger assembly and the COF air-water separator by detecting water within 2 mm of the sensor element surface. The sensor has been designed to fit flush with duct wall, with no intrusion into the air flow. The sensor surface has a fused glass finish with very low porosity and near zero water retention, and is able to detect extremely small levels of moisture. The LCOS design is based on a capacitive technology which is largely insensitive to contaminants, unlike competitive resistive technologies, thereby ensuring maintenance free, long lifetime performance which is a requirement of all ISS applications.This paper describes performance testing of the LCOS, and details some of the design features unique to this type of sensor.