Simple modelling functions for the properties of steam and water were developed for PC applications. The properties were modelled by quadratic function to reduce the number of coefficients and, thereby, the necessary computing time. Computer programs were written to compute the unknown coefficients as well as evaluate the accuracy of the functions. It was found that the functions can be defined with sufficient accuracy for practical use. At the same time, their short computing time, which averaged about 7% of those for IFC67 functions, makes them attractive to PC applications.