The thermophysical properties of water are important in the design and optimization of many processes. An international organization (IAPWS, the International Association for the Properties of Water and Steam) sets standards for the representation of these properties; the two important standards for thermodynamic properties (one `for industrial use,' tailored to the needs of the steam power industry, and one `for general and scientific use') have both changed in the past few years. This article describes the IAPWS standards, gives guidelines on when it is appropriate to use which formulation, and alerts readers to challenges they might face when updating from obsolete property formulations to the current standards.

• Contact: Allan Harvey