Fuel Demand Model is a thermodynamic model-based system for combined water and power plants (IPP and IWPP) which predicts the oil/gas demand based on the existing load and environmental conditions. It combines the complete thermodynamic model of the power and desalination plant. The model is developed based on the various environmental and plant demand conditions. Based on the existing demand in the desalination plant, the FDM predicts the appropriate amount of steam and fuel required to be utilized.