In today's world of low cost personal computers and advanced software combined with knowledge of mathematical modeling MSF plant operation it is relatively simple and essential to develop a computer operational simulation program for any large desalination system. Such a computer program provides the following benefits: It's FUN and inexpensive. It will aid in finalizing the design and optimization. It will determine operating costs at any set of variable input parameters. It can be used to determine the overall algorithm for operating costs and establish set-point parameters for operating conditions.