To achieve a highly effective, easy to operate, electrical potential-driven water treatment process, three main areas have been investigated. First, a three-dimensional geometry-based equilibrium model is developed to fully describe the potential overlapping regimes from micro- to macro- pores in electrical double layers using the finite size of hydrated ions. Second, a membrane capacitive deionization (MCDI) is developed to achieve calcium-selective removal in an electrosorption process. Last, but not least, the ion-removal performance of a layered double hydroxide MCDI electrode is evaluated for the removal of lead ions in water.