Process for the production of monochloramine characterized in that it provides for: - drawing a portion of water intended for a user (U1..Un) and exclusively using said portion for preparing a monochloramine solution; - subjecting said portion intended for preparing the monochloramine solution to a treatment on osmotized membrane, - making said treated portion of water eact with reagents (A, B) in a cylindrical-based internal reactor whose lower base bears an outlet mouth for the connection with produced monochloramine storage tank, while the upper base of the reactor bear two orifices (A,B) through which the reagent and reagent enter which take part in the reaction and wherein the entrance of the reagents (A, B) is in the same axial direction as said cylindrical-based reactor, the reactor further bears a orifice for the entrance of the treated portion water on a plane parallel to the base of said cylindrical-based reactor, in non-radial direction, by means of micrometric regulation of a charging solenoid valve, the aforesaid orifice being laterally arranged in the lateral cylindrical jacket of the reactor; a point inside the reactor identifies the point of contact between the introduction of the reagent and of the treated water. - and wherein said reaction provides for, simultaneously with the entrance of the treated portion water in the cylindrical-based reactor: ∘ introduction of the reagent comprising an ammonium solution in salt form, through an orifice; once a defined time has elapsed or a preset level has been reached, ∘ introduction of the reagent, comprising stabilized sodium hypochlorite, through a third orifice; in said step, treated portion water continues to flow into in the cylindrical-based reactor; ∘ introduction of treated portion water in the reactor until a final level is reached, ∘ measurement of the pH of the pure monochloramine solution produced and verification that said value falls within a range between 8 - 12; in positive case, the method provides ∘ discharging of the solution produced in the reactor towards a storage tank, rendering the monochloramine produced by the reaction available for use; otherwise if the read value is outside the range 8- 12, the method provides generating an alarm from the PLC to block the production and eliminate all that produced outside the aforesaid range. - drawing a portion of water intended for a user (U1..Un) and exclusively using said portion for preparing a monochloramine solution; - subjecting said portion intended for preparing the monochloramine solution to a treatment on osmotized membrane, - making said treated portion of water eact with reagents (A, B) in a cylindrical-based internal reactor whose lower base bears an outlet mouth for the connection with produced monochloramine storage tank, while the upper base of the reactor bear two orifices (A,B) through which the reagent and reagent enter which take part in the reaction and wherein the entrance of the reagents (A, B) is in the same axial direction as said cylindrical-based reactor, the reactor further bears a orifice for the entrance of the treated portion water on a plane parallel to the base of said cylindrical-based reactor, in non-radial direction, by means of micrometric regulation of a charging solenoid valve, the aforesaid orifice being laterally arranged in the lateral cylindrical jacket of the reactor; a point inside the reactor identifies the point of contact between the introduction of the reagent and of the treated water. - and wherein said reaction provides for, simultaneously with the entrance of the treated portion water in the cylindrical-based reactor: ∘ introduction of the reagent comprising an ammonium solution in salt form, through an orifice; once a defined time has elapsed or a preset level has been reached, ∘ introduction of the reagent, comprising stabilized sodium hypochlorite, through a third orifice; in said step, treated portion water continues to flow into in the cylindrical-based reactor; ∘ introduction of treated portion water in the reactor until a final level is reached, ∘ measurement of the pH of the pure monochloramine solution produced and verification that said value falls within a range between 8 - 12; in positive case, the method provides ∘ discharging of the solution produced in the reactor towards a storage tank, rendering the monochloramine produced by the reaction available for use; otherwise if the read value is outside the range 8- 12, the method provides generating an alarm from the PLC to block the production and eliminate all that produced outside the aforesaid range. ∘ introduction of the reagent comprising an ammonium solution in salt form, through an orifice; once a defined time has elapsed or a preset level has been reached, ∘ introduction of the reagent, comprising stabilized sodium hypochlorite, through a third orifice; in said step, treated portion water continues to flow into in the cylindrical-based reactor; ∘ introduction of treated portion water in the reactor until a final level is reached, ∘ measurement of the pH of the pure monochloramine solution produced and verification that said value falls within a range between 8 - 12; in positive case, the method provides ∘ discharging of the solution produced in the reactor towards a storage tank, rendering the monochloramine produced by the reaction available for use; otherwise if the read value is outside the range 8- 12, the method provides generating an alarm from the PLC to block the production and eliminate all that produced outside the aforesaid range.