Electrodialysis with ion exchange membranes is one of the most important membrane methods, which deals with the problems of desalination of salted waters, waste water minimization, production of ultra-pure water, concentration of dilute solutions, separation of electrolytes and non-electrolytes and with the production of acids and alkalis from their salts. Mathematical modelling and laser interferometry have been applied for calculation and visualisation of local characteristics under electrodialysis demineralization.