A water-jet operating head for cutting materials with a hydro-abrasive high pressure jet, including: - a head main portion, intended to be mounted on an operating machine, and defining an axial passage for feeding a high pressure water flow, - a nozzle-carrying support which is removably connected to the head main portion, - a jet focusing nozzle for emitting a high pressure hydro-abrasive jet, mounted within said nozzle-carrying support and defining an ejection passage which is arranged downstream of said feeding passage and is in communication therewith, - a primary nozzle (13, 13a) carried by said nozzle-carrying support upstream of the focusing nozzle and having a body with an orifice (14, 14a) of predetermined diameter interposed in the communication between the water flow feeding passage and the hydro-abrasive jet ejecting passage, and - at least one connecting element carried by said head, through which an abrasive agent can be fed into the high pressure water flow at a mixing chamber defined within the nozzle-carrying support, between the primary nozzle (13, 13a) and the focusing nozzle, wherein: - said connecting element is carried by said head main portion and therefore remains associated therewith when the aforesaid nozzle-carrying support is removed from said main portion, said head being characterized in that - said head main portion comprises a main support defining a cylindrical cavity and said nozzle-carrying support comprises a body adapted to be slidably and removably received within said cylindrical cavity of said main support, and - said head further comprises a locking element for axially locking the nozzle-carrying support in its coupling position within said main support, said locking element being switchable between an operative condition and an inoperative condition. - a head main portion, intended to be mounted on an operating machine, and defining an axial passage for feeding a high pressure water flow, - a nozzle-carrying support which is removably connected to the head main portion, - a jet focusing nozzle for emitting a high pressure hydro-abrasive jet, mounted within said nozzle-carrying support and defining an ejection passage which is arranged downstream of said feeding passage and is in communication therewith, - a primary nozzle (13, 13a) carried by said nozzle-carrying support upstream of the focusing nozzle and having a body with an orifice (14, 14a) of predetermined diameter interposed in the communication between the water flow feeding passage and the hydro-abrasive jet ejecting passage, and - at least one connecting element carried by said head, through which an abrasive agent can be fed into the high pressure water flow at a mixing chamber defined within the nozzle-carrying support, between the primary nozzle (13, 13a) and the focusing nozzle, wherein: - said connecting element is carried by said head main portion and therefore remains associated therewith when the aforesaid nozzle-carrying support is removed from said main portion, said head being characterized in that - said head main portion comprises a main support defining a cylindrical cavity and said nozzle-carrying support comprises a body adapted to be slidably and removably received within said cylindrical cavity of said main support, and - said head further comprises a locking element for axially locking the nozzle-carrying support in its coupling position within said main support, said locking element being switchable between an operative condition and an inoperative condition. - said connecting element is carried by said head main portion and therefore remains associated therewith when the aforesaid nozzle-carrying support is removed from said main portion, said head being characterized in that - said head main portion comprises a main support defining a cylindrical cavity and said nozzle-carrying support comprises a body adapted to be slidably and removably received within said cylindrical cavity of said main support, and - said head further comprises a locking element for axially locking the nozzle-carrying support in its coupling position within said main support, said locking element being switchable between an operative condition and an inoperative condition.