A water treatment device comprising an external body and an internal body assemblable to one another, wherein: the external body has a shape which is such as to comprise a lateral surface and two heads (11, 12) opposite one another, and comprises a water inlet, for inlet of a water flow in arrival from a water distribution network, situated on the lateral surface in proximity of a first head and a water outlet at a second head, the external body is conformed so as to comprise an axial housing, accessible from the first head, to couplingly receive the internal body, the axial housing being in communication with the water inlet and with the water outlet, the internal body is conformed so as to comprise a complementary shape to the axial housing of the external body so as to be insertable in the axial housing through a hole in the first head of the external body, wherein the walls of the axial housing and the walls of the internal body are reciprocally conformed in such a way that, when the internal body is inserted in the axial housing, to identify between them a spiral pathway for the water flow between the water inlet and the water outlet so that the water flow in arrival from the water distribution network, entering through the water inlet, is forced to follow a vortex pathway, characterized in that the water outlet is realised on the second head in a position that is coaxial to the axis of the spiral pathway of the water flow, in that the internal body is conformed in such a way as to have a truncoconical shape and to have a spiral-shaped incision on the lateral surface of the truncoconical shape and wherein the axial housing of the external body is conformed so as to have a truncoconical shape that is complementary to the truncoconical shape of the internal body, and wherein, when the internal body is inserted in and coupled in the axial housing of the external body, the spiral-shaped incision defines, between the walls of the internal body and the walls of the axial housing, the spiral pathway for the water flow between the water inlet and the water outlet having an axis that is coaxial to the axial housing of the external body and coaxial to the water outlet, and in that the external body has a connection between the water inlet and the axial housing and wherein the spiral-shaped incision is realised on the walls of the internal body so that, when the internal body is inserted in and coupled with the axial housing of the external body, it has an initial portion of spiral at the position of the connection. the external body has a shape which is such as to comprise a lateral surface and two heads (11, 12) opposite one another, and comprises a water inlet, for inlet of a water flow in arrival from a water distribution network, situated on the lateral surface in proximity of a first head and a water outlet at a second head, the external body is conformed so as to comprise an axial housing, accessible from the first head, to couplingly receive the internal body, the axial housing being in communication with the water inlet and with the water outlet, the internal body is conformed so as to comprise a complementary shape to the axial housing of the external body so as to be insertable in the axial housing through a hole in the first head of the external body, wherein the walls of the axial housing and the walls of the internal body are reciprocally conformed in such a way that, when the internal body is inserted in the axial housing, to identify between them a spiral pathway for the water flow between the water inlet and the water outlet so that the water flow in arrival from the water distribution network, entering through the water inlet, is forced to follow a vortex pathway, characterized in that the water outlet is realised on the second head in a position that is coaxial to the axis of the spiral pathway of the water flow, in that the internal body is conformed in such a way as to have a truncoconical shape and to have a spiral-shaped incision on the lateral surface of the truncoconical shape and wherein the axial housing of the external body is conformed so as to have a truncoconical shape that is complementary to the truncoconical shape of the internal body, and wherein, when the internal body is inserted in and coupled in the axial housing of the external body, the spiral-shaped incision defines, between the walls of the internal body and the walls of the axial housing, the spiral pathway for the water flow between the water inlet and the water outlet having an axis that is coaxial to the axial housing of the external body and coaxial to the water outlet, and in that the external body has a connection between the water inlet and the axial housing and wherein the spiral-shaped incision is realised on the walls of the internal body so that, when the internal body is inserted in and coupled with the axial housing of the external body, it has an initial portion of spiral at the position of the connection.