In a liquid crystalline (LC) monolayer on liquid surface, simple rod-like chiral molecules exhibit a unidirectional rotational motion under transmembrane water transport. The coherent collective precession motion was observed in various chiral LC monolayers, the rotational speed of which is linearly increased with the chirality strength and also the transmembrane water transfer rate per unit of time. When either the chirality or water transfer direction is inversed, the rotational direction of the precession is completely reversed. The result indicates that the molecular chirality works as a propeller and its unidirectional rotation is driven by water transfer across the membrane. Each chiral molecule cannot overcome the thermal fluctuation alone, but the LC interaction amplifies the molecular motion and transforms it into a coherent collective precession of entire molecules. This might propose a new approach to nanomachines.