Abstract: A method of detecting the presence of moisture adjacent the exterior side of tubes in a pipe system such as a subterranean district heating system of insulated tubes, whereby it is measured or registered whether an electrical conductivity exists between two electric conductors permanently positioned immediately adjacent the tube in supposed dry and electrical insulating but hygroscopic surroundings. Furthermore, a pipe system and a pipe having means for facilitating the use of the said method, these means comprising one or more electrical conductors extending along each pipe embedded in the insulating material surrounding the pipe.