Capacitive de-ionisation is emerging as a viable technology for water desalination. The technique is based on electrochemical fundamentals: it rests on the potential-dependent adsorption of ions within the pores of high surface area electrode materials. The adsorption process is normally capacitive, although Faradaic approaches have been reported recently. Most of the rapidly expanding literature on this topic focusses on the material science aspects: namely the effect of electrode and membrane composition/structure on the performance metrics associated with this technique. In this short review, we focus on how electrochemical methods can be used to further understanding of this promising technology for water purification. We also highlight complementary analytical techniques which can be applied in tandem with the electrochemical signals.