The dynamo-electrical turbo generator assembly is incorporated in a domestic water heater provided with a water flow (19), the turbo generator assembly (1,2) includes a longitudinal portion of conduit pipe (7) fitted with a discharge valve (8), and having an internal flat wall (7c) dividing the water flow (19) and forming a branch conduit (18) for impelling the turbine wheel (5). The drive shaft (4) common with the magnet rotor (3) of the alternator (2) is positioned offset to a central plane (E) for the formation of a tangential outlet (20) for the water flow (18') towards the wheel vanes (5). A moulded plastic alternator body (6) provided with a chamber (14) housing the rotor, is mounted on said portion of conduit pipe (7) and crossed by the common drive shaft (4). A coupling means (6b,7b) of the alternator body (6) is provided to the portion of conduit pipe (7).