Method for reducing the microbial load of a liquid comprising the following phases: a. providing at least one treatment module comprising: - at least one tubular conduit having at least one portion transparent to infrared radiation; - three sources (16a, 16b, 16c) of infrared radiation located in the vicinity of said portion transparent to infrared radiation, said three sources (16a, 16b, 16c) being positioned along a direction parallel to the longitudinal axis of said tubular conduit, at a distance r from each other, and being configured to transmit at least one infrared radiation; b. making the liquid flow into said tubular conduit; c. exposing the liquid while it flows inside the tubular conduit to the infrared radiation emitted by said three sources (16a, 16b, 16c); wherein the liquid flowing inside the tubular conduit is treated according to an irradiation sequence comprising: i) first exposure of the liquid to infrared radiation for a time within the range 0.1 - 5 seconds, which is a first heating phase; ii) second exposure of the liquid to infrared radiation for a time within the range 0.2 - 10 seconds, which is a second heating phase; iii) third exposure of the liquid to infrared radiation for a time within the range 1.5 - 15 seconds, which is a third heating phase; wherein said phases i), ii) and iii) are interspersed with periods of non-exposure of the liquid to infrared radiation of duration within the range 0.1 - 7 seconds. seconds, which are cooling phases. a. providing at least one treatment module comprising: - at least one tubular conduit having at least one portion transparent to infrared radiation; - three sources (16a, 16b, 16c) of infrared radiation located in the vicinity of said portion transparent to infrared radiation, said three sources (16a, 16b, 16c) being positioned along a direction parallel to the longitudinal axis of said tubular conduit, at a distance r from each other, and being configured to transmit at least one infrared radiation; - at least one tubular conduit having at least one portion transparent to infrared radiation; - three sources (16a, 16b, 16c) of infrared radiation located in the vicinity of said portion transparent to infrared radiation, said three sources (16a, 16b, 16c) being positioned along a direction parallel to the longitudinal axis of said tubular conduit, at a distance r from each other, and being configured to transmit at least one infrared radiation; b. making the liquid flow into said tubular conduit; c. exposing the liquid while it flows inside the tubular conduit to the infrared radiation emitted by said three sources (16a, 16b, 16c); wherein the liquid flowing inside the tubular conduit is treated according to an irradiation sequence comprising: i) first exposure of the liquid to infrared radiation for a time within the range 0.1 - 5 seconds, which is a first heating phase; ii) second exposure of the liquid to infrared radiation for a time within the range 0.2 - 10 seconds, which is a second heating phase; iii) third exposure of the liquid to infrared radiation for a time within the range 1.5 - 15 seconds, which is a third heating phase; i) first exposure of the liquid to infrared radiation for a time within the range 0.1 - 5 seconds, which is a first heating phase; ii) second exposure of the liquid to infrared radiation for a time within the range 0.2 - 10 seconds, which is a second heating phase; iii) third exposure of the liquid to infrared radiation for a time within the range 1.5 - 15 seconds, which is a third heating phase; wherein said phases i), ii) and iii) are interspersed with periods of non-exposure of the liquid to infrared radiation of duration within the range 0.1 - 7 seconds. seconds, which are cooling phases.