Quasi-elastic neutron spectroscopy was used to study the changes in the water content of hydrated tricalcium silicate cement paste with decreasing relative humidity (RH). The structurally bound water was divided into water bound in Ca(OH)2 and in calcium-silicate hydrate, or C–S–H-gel, utilizing the inelastic vibrational modes of Ca(OH)2. The quasi-elastic line was analyzed in terms of free and constrained water, and both were observed to decrease as the pores empty of pore-water with drying. An inelastic line related to translational vibrations of immobile water molecules was also extracted from the spectra, and its intensity was found to decrease with lower RH.