A method of structural analysis, based on restricted averages of the angular pair correlation function, is proposed and applied to liquid water. Minimum free energy paths for a molecule moving in an average local structure are obtained. Around a central molecule, accepting and donating neighbors form hydrogen bonds having the same energy minima but differing for the availability of low free energy states. Some bounded sates have specific bridging functions and connect hydrogen-bond and transition states along negative free energy pathways, thus favoring local diffusion. Bridging and transition states play the role of structural defects and include bifurcated hydrogen-bond and interstitial water geometries. Our methods and results can be relevant to understand, from a structural point of view, the anomalous behavior of stressed and confined water. (C) 1997 American Institute of Physics. [S0021-9606(97)50547-2].