The structure at the liquid/solid interface of synthetic saponites is monitored by NMR methods. These results are compared with data obtained with a natural saponite. The mean orientation of interfacial water molecules is different for synthetic and natural saponites. Interaction of water molecules or counterions with the solid surface depends on the charge layer of the synthetic clays. Water/acetonitrile and sodium/tetrapropylammonium cation competitions have been studied. Significant changes of the orientation of interfacial water molecules and removal of sodium counterions are observed only with the lowest charged saponite.