Thermodynamic equations for electrolytes were used to calculate the gypsum scaling potential of the feed water based on its ionic composition. The extent of concentration polarization at the membrane surface was determined from the film model. A proportionality factor relating the kinetic difference between the saturation predicted by the gypsum solubility model and the actual crystallization was obtained from glassware experiments. Lastly, a parabolic equation relating antiscalant (polyacrylic acid) dose to the normalized concentration factors of the saline solution was experimentally developed. These theoretical and experimental parameters were combined into a single model for predicting the required antiscalant dose to control calcium sulfate scale in nanofiltration membranes for any given saline solution. The model was tested with model solutions simulating saline agricultural drainage waters. Includes 14 references, tables, figures.