An insulated pipe includes an elongated tube having a first end, a second end, and a sidewall extending therebetween, including an inner surface and an outer surface. The insulated pipe also includes an insulating member covering a portion of the outer surface of the sidewall and a planar moisture sensor. The planar moisture sensor is positioned in the insulating member or between the insulating member and the outer surface of the tube sidewall. The planar moisture sensor includes: a first electrode having a flat conductive member having an inner surface and an outer surface; a second electrode spaced apart from the first electrode having a flat conductive member having an inner surface and an outer surface, and a dielectric layer. The dielectric layer includes an absorbent dielectric polymer material positioned between and in electrical contact with the inner surfaces of the first electrode and the second electrode.