Apparatus, system and method for monitoring external properties of plant equipment and/or pipe work

A sensor system for detecting the presence of water at a plurality of depth locations within an insulating material, the sensor system comprising:

• a first sensing means and a second sensing means;
• wherein the first sensing means is operable to provide a first sensor output indicative of the presence of water at a first depth location in the insulating material;
• and
• wherein the second sensing means is operable to provide a second sensor output indicative of the presence of water at a second depth location in the insulating material;
• wherein the sensor system comprises at least one sensor having an elongate body configured to be inserted into an insulating material;
• wherein the first sensing means is located on the elongate body;
• and
• wherein the first depth location corresponds to the location of the first sensing means on the elongate body;
• and
• wherein the first sensing means and/or second sensing means is a capacitive sensing means, the capacitive sensing means comprising at least two electrodes spaced apart from one another on the elongate body and a means for determining the capacitance value between the at least two electrodes.