The hydration of natural or synthetic macromolecules is of fundamental importance in our understanding of their structure and stability. Quantification of hydration water can promote the understanding to many complex biological mechanisms such as protein folding, as well as the dynamics and conformation of polymers. An approach to quantification of solvent water was developed by dielectric spectroscopy. Dielectric behaviors of PNIPAM microgels with different crosslink density distribution were measured in the range of 0.5-40 GHz and 15-50. An obvious relaxation process caused by free and bound water was found. Dielectric parameters of free and bound water show that the crosslink density distribution does not affect the volume phase transition temperature of microgels, but significantly influence the orientation dynamics of the solvent water. We found that the three kinds of microgel can be distinguished by the dielectric parameters of the bound water. In addition, the number of water in and outside microgel during the volume phase transition process was quantitatively calculated for the first time. This study provides the possibility for the quantification of water in complex biological process. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1859-1864