We studied the behavior of absorbed water in equilibrium-swollen poly(vinyl alcohol) derivative hydrogels by differential scanning calorimetry (DSC), H-1 nuclear magnetic resonance, and wide-angle X-ray diffraction. By DSC, three types of water were detected, and their relative fractions were estimated. With this technique we also calculated the pore size for every sample. From the nonexponential decay of the spin-spin relaxation data, we distinguished two environmental states of the absorbed water in the samples. The relaxation times were determined. From these data, we calculated the fractions of each type of water for every hydrogel and related them to the degree of crosslinking. The X-ray study indicated that the water absorbed in these hydrogels forms a single crystalline phase on cooling. (C) 2003 Wiley Periodicals, Inc.