Abstract: The fixed-direction jet units (1) of a whirlpool-bath system each include a nozzle (18) for supplying water under pressure from a tube-section (17) to an outlet (12) across an air gap (20) within a chamber (19). The unit (1) is clamped to the bath-wall (14) between a flange (16) of the outlet (12) and the unit housing (15). The flow of water from the nozzle (18) across the gap (20) into the axially-aligned stem (13) of the outlet (12) draws air into the chamber (19) from an inlet pipe (21) that is coupled to a distribution manifold (7) of an air-supply controller (9) by an individual supply tube (8). A circumferential skirt (22) projects backwardly from the stem (13) to shroud the gap (20) over a frusto-conical nose-part (23) of the nozzle (18), so that air is constricted to enter the gap (20) through the annular space (24) between them.