Hydrothermal and supercritical water processes Hydrothermal and Supercritical Water Processes presents an overview on the properties and applications of water at elevated temperatures and pressures. It combines fundamentals with production process aspects. Water is an extraordinary substance. At elevated temperatures (and pressures) its properties change dramatically due to the modifications of the molecular structure of bulk water that varies from a stable three dimensional network formed by hydrogen bonds at low and moderate temperatures to an assembly of separated polar water molecules at high and supercritical temperatures