This paper considers the design of multistage dialysis plant used in the desalination of brackish or saline water. It establishes the optimum applied voltage profiles to minimise power requirements for the operation. A simple model is developed to expand the optimisation algorithm. Plant stages operating in fully mixed regime and in ’plug-flow’ modes are considered and they are compared with an ideal plant that has an infinite number of stages. Sample results together with calculations are used to illustrate the theory.