The present invention relates to a wetness detector system that rapidly detects the presence of wetness due to a liquid leak in a system. The wetness detector system contains a reusable wetness sensor that is able to accurately detect the presence of wetness and, in the case of an extracorporeal blood treatment, the presence of blood. The wetness detector system can quickly alert both a user and medical personnel that a liquid leak has been detected in a treatment system and, if necessary, halt the removal of liquids and/or blood from the patient. If a liquid leak is not detected for a period of time, the wetness sensor can enter a low power state, extending the life of the device. The wetness detector system can monitor a number of wetness sensors simultaneously, which would, for example, eliminate the need for medical personnel to continuously inspect numerous patients visually for potentially fatal blood leaks due to needle dislodgement during an extracorporeal blood treatment.