Methodology for detection and localization of leakages, in underground pipelines, based on the principle of the microwave reflectometry, through an apparatus comprising of a reflectometric unit, an electronic calculator, a sensing element made of electrically conductive material placed on the road surface in correspondence of the underground metal pipe, accessories for electrical connection between the reflectometric unit and the underground pipe and accessories for electrical connection between the reflectometric unit and the sensing element, said methodology characterized by the following steps: (i) setting of a sensing element, which, together with the metal pipe acts as transmission line wherein the electrical connection between the sensing element and the reflectometric unit is realized through a coaxial cable with an electrical impedance approximately equal to the output impedance of the reflectometric unit and wherein the electrical connection is realized through a unipolar cable to be connected between a point of access to the pipe thus allowing the electrical continuity between the pipe and the reflectometric unit; (ii) sending of an electromagnetic signal from the unit that propagates through a transmission line consisting of the sensing element and the underground pipe; (iii) detection of the reflectometric signal; (iv) visualization and interpretation of the reflectometric signal as a function of time or, alternatively, as a function of the corresponding apparent distance which is function of dielectric properties of the soil between said underground pipe and said sensing element, with a particular emphasis on water loss; (v) individuation of the significant dielectric variations associated to the detected reflectometric signal (typically those corresponding to the presence of a relative maximum or minimum) with particular emphasis on water loss; (vi) localization of the possible leakage event at a distance L 1 from the measuring point and L 2 from the terminating element; (vii) calibration between the reference known distance L 1 + L 2 and the corresponding measured apparent distance for evaluating the correct spatial localization of the leak; (viii) implementation of specific signal filtering to improve the interpretation of the reflectometric detection. (i) setting of a sensing element, which, together with the metal pipe acts as transmission line wherein the electrical connection between the sensing element and the reflectometric unit is realized through a coaxial cable with an electrical impedance approximately equal to the output impedance of the reflectometric unit and wherein the electrical connection is realized through a unipolar cable to be connected between a point of access to the pipe thus allowing the electrical continuity between the pipe and the reflectometric unit; (ii) sending of an electromagnetic signal from the unit that propagates through a transmission line consisting of the sensing element and the underground pipe; (iii) detection of the reflectometric signal; (iv) visualization and interpretation of the reflectometric signal as a function of time or, alternatively, as a function of the corresponding apparent distance which is function of dielectric properties of the soil between said underground pipe and said sensing element, with a particular emphasis on water loss; (v) individuation of the significant dielectric variations associated to the detected reflectometric signal (typically those corresponding to the presence of a relative maximum or minimum) with particular emphasis on water loss; (vi) localization of the possible leakage event at a distance L 1 from the measuring point and L 2 from the terminating element; (vii) calibration between the reference known distance L 1 + L 2 and the corresponding measured apparent distance for evaluating the correct spatial localization of the leak; (viii) implementation of specific signal filtering to improve the interpretation of the reflectometric detection.