We propose to perform a systematic study of the intermolecular librational mode of molecular water in the proton conducting hydrated alkali thio-hydroxogermanates M2GeS2(OH)2*yH2O (M = K, Rb, Cs, y~1). Our previous results suggest that the water molecules are confined to cages with a characteristic size of about 7 Å, built up of the thio-oxoanions and alkali ions. The results also show that the characteristic size of these cages increases with the size of the alkali ion. We expect that this will affect the librational motions of the water molecules, which are important for the transport of protons. Thus, we plan to investigate the degree of confinement on the local librational motions of the water molecules and relate this to the proton conductivity of the investigated materials.