This paper deals with a heuristic optimal strategy for the parameters of a PI controller to be applied in a system used for the regeneration of potable water. Because of the presence of a saturation an anti-windup control structure is considered to manage saturation effects. In order to analyse the stability and the dynamic performance of the controlled system a Lyapunov approach is proposed. Through this approach the condition of the three parameters which characterise the controller (PI and anti-windup scheme) are calculated to obtain a compromise between stable fast dynamics and and an optimality according to a chosen cost function to be minimised. The method consists of increasing the parameter of the proportional controller until the step answer of the controlled system equals the desired settling time. After that a heuristic optimisation algorithm is applied for setting up the other parameters of the controller. Simulations using real parameters of the system are shown.