A sensor system for detecting the presence of water in an insulating material (16, 116, 616, 716, 816, 916, 1016) surrounding plant equipment and/or pipe work, the sensor system comprising: a plurality of sensors located in and spatially distributed over the insulating material, each sensor being operable to provide a sensor output indicative of the presence of water in an insulating material; at least one reference sensor operable to provide a reference sensor output indicative of the presence of water in an ambient environment in the vicinity of the plurality of sensors; and a processor configured to receive the sensor outputs from the plurality of sensors and the reference sensor output; wherein the processor is configured to correlate the sensor outputs from the plurality of sensors and the reference sensor output to identify whether: - one or more of the plurality of sensors has a sensor output which closely follows the reference sensor output to determine that the one or more of the plurality of sensors is located in a substantially dry portion of the insulating material (16, 116, 616, 716, 816, 916, 1016); or - one or more of the plurality of sensors has a sensor output which deviates from the reference sensor output to determine that the one or more of the plurality of sensors is located in a substantially wet portion of the insulating material (16, 116, 616, 716, 816, 916, 1016), and provide a correlation data output for use in evaluating a corrosion condition. a plurality of sensors located in and spatially distributed over the insulating material, each sensor being operable to provide a sensor output indicative of the presence of water in an insulating material; at least one reference sensor operable to provide a reference sensor output indicative of the presence of water in an ambient environment in the vicinity of the plurality of sensors; and a processor configured to receive the sensor outputs from the plurality of sensors and the reference sensor output; wherein the processor is configured to correlate the sensor outputs from the plurality of sensors and the reference sensor output to identify whether: - one or more of the plurality of sensors has a sensor output which closely follows the reference sensor output to determine that the one or more of the plurality of sensors is located in a substantially dry portion of the insulating material (16, 116, 616, 716, 816, 916, 1016); or - one or more of the plurality of sensors has a sensor output which deviates from the reference sensor output to determine that the one or more of the plurality of sensors is located in a substantially wet portion of the insulating material (16, 116, 616, 716, 816, 916, 1016), - one or more of the plurality of sensors has a sensor output which closely follows the reference sensor output to determine that the one or more of the plurality of sensors is located in a substantially dry portion of the insulating material (16, 116, 616, 716, 816, 916, 1016); or - one or more of the plurality of sensors has a sensor output which deviates from the reference sensor output to determine that the one or more of the plurality of sensors is located in a substantially wet portion of the insulating material (16, 116, 616, 716, 816, 916, 1016), and provide a correlation data output for use in evaluating a corrosion condition.