Here is an amazing website which provides an open-source freely available version of the steam tables in various formats. I mirrored the user-guide and the actual program on Scribd, just in case.
The program is saved as XSteam.m.txt, which you will have to rename as XSteam.m after downloading, for Octave or Matlab to recognize it natively.
Here's the attribution/disclaimer.
Water and steam properties according to IAPWS IF-97
By Magnus Holmgren, www.x-eng.comThe steam tables are free and provided as is. We take no responsibilities for any errors in the code or damage thereby. You are free to use, modify and distribute the code as long as authorship is properly acknowledged. Please notify me at firstname.lastname@example.org if the code is used in commercial applications.