Hydrated nanocrystalline calcium hydroxyapatite was studied using unconventional solid-state NMR technique with cross-polarization from phosphorus-31 to protons (P-31 -> H-1 CP) under magic-angle spinning (MAS). Two peaks were detected: at 0.0 ppm from structural hydroxyl groups and at 5.4 ppm from water. Their intensities were monitored as a function of the contact time. It was found that there were two types of water adsorbed on the crystal surface: typical strongly bound water and distinct, more mobile water associated with a particular P-31 environment capable of fast spin-lattice relaxation in the rotating frame. Relative contents of protons in various material compartments were estimated. (C) 2012 Elsevier B.V. All rights reserved.