The apparent biocompatibility of many synthetic and natural aqueous gel materials has encouraged their study and testing for a wide variety of biomedical device applications. Many of the physical and in particular the interfacial properties of such gels are highly dependent on the organization of water within and on the surface of the hydrogel. Water is an important component of such gels, varying from about 30 to nearly 100 wt-%, yet the role of water in the gels has been virtually ignored. This paper briefly reviews the nature of water structure in pure bulk water, in solutions, and at interfaces. Polywater or anomalous water is also briefly reviewed. Evidence is presented that the water in many hydrogel systems can exist in at least three different, structurally distinct forms. A hypothesis is presented which can be used to evaluate and study the nature of water in bulk hydrogels. Consideration is also given to the role of organized water at the hydrogel surface on the interfacial properties of such systems.