All the formulation for the prediction of water properties are published by International Association for the Properties of Water and Steam (IAPWS) so that they can be used.
It is often important to use exactly the same correlations so that that all the thermodynamic data are self-consistent. Therefore the formulations are standardized by an international body.
I do not think that the use of this formulae is in any way restricted because such restriction would defeat the very purpose - standarization.
for the collection of the current formulations.
There may be a restriction for a particular implementation (computer program) or sets of tables ( "lookup tables" and interpolation are often used for performance). Not sure.
Hope someone starts an extension to implement these kind of things in Gnumeric.
Cheers. Ephraim the horse.