A new universal approach based on the concept of preferential structure fluctuations has been used to describe the structure of fluids in the liquid and supercritical states. It has been shown that the structure of fluids can be presented as a limited set of thermodynamically beneficial molecular configurations arising as a result of fluctuations of the nearest environment. When applied to the structure of liquid and supercritical water, this concept allows us to explain the unexpected response of the water structure to strong compression and the unusual behavior of the pair correlation function at supercritical temperatures, and to examine the temperature dependence of hydrogen bonding. The physical state of the supercritical phase of water has also been analyzed, which is of practical significance. It is also important that some inferences drawn from the study of liquid and supercritical water can be extended to the whole class of fluids.