In this work, a model for the development of scale formation in once-through (OT) and brine-recycle (BR) multi-stage flash (MSF) distiller is presented. The model begins to calculate the carbonate species and sulfate concentrations in the seawater feed and follow the path of the feed from the last stage to the first stage reaching the top brine temperature (TBT). The changes in the carbonate and sulfate scale are shown. As a net result, fouling factor increases with increasing the temperature. The developed model is validated with the experimental results when anti-scalant is used from literature. It is important to note that the plant cannot be operated without using anti-scalant because of the hard scale problem threatening the performance and materials of the MSF plant, which is, in fact, the strong point of the model. The model can be used to check the pretreatment efficiency. (C) 2014 Elsevier B.V. All rights reserved.